Note: Descriptions are shown in the official language in which they were submitted.
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DETECTING AND MINIMIZING EFFECTS OF OPTICAL NETWORK FAULTS
RELATED APPLICATIONS
This application is: i) a Continuation of U.S. Application No. 11/651,329
entitled "Method and Apparatus for Rogue Tolerant Ranging and Detection,"
filed
January 8, 2007, which: (i.1) claims the benefit of U.S. Provisional
Application No.
60/848,955, entitled "Method and Apparatus for Rogue Tolerant Ranging and
Detection," filed on October 3, 2006; and i.2) which is a Continuation-In-Part
of
U.S. Application No. 11/515,504 entitled "Method and Apparatus for Identifying
a
Passive Optical Network Failure," filed on September 1, 2006 which: i.2.a)
claims
1.0 the benefit of U.S. Provisional Application No. 60/793,748; filed on April
21, 2006;
and i.2.b) 11/515,504 also is a Continuation-In-Part of U.S. Application No.
11/514,461 entitled "Method and Apparatus for Diagnosing Problems on a Time
Division Multiple Access (TDMA) Optical Distribution-Network (ODN)," filed on
August 31, 2006, which claims the benefit of U.S. Provisional Application No.
60/789,357, filed on April 5, 2006; and this application is also: ii) a
Continuation of
U.S. Application No. 11/514,421 entitled "Method and Apparatus for ONT Ranging
with Improved Noise Immunity," filed on September 1, 2006, which is: ii.1) a
Continuation-In-Part of U.S. Application No. 11/432,292 entitled "Method and
Apparatus for ONT Ranging with Improved Noise Immunity," filed on May 10,
2006; and which is ii.2) a Continuation-In-Part of U.S. Application No.
11/514,461
entitled "Method and Apparatus for Diagnosing Problems on a Time Division
Multiple Access (TDMA) Optical Distribution Network (ODN)," filed on August
31, 2006; 11/432,292 and 11/514,461 claim the benefit of U.S. Provisional
Application No. 60/789,357, filed on April 5, 2006. The entire teachings of
the
above applications are incorporated herein by reference.
BACKGROUND OF THE rNVENTION
A passive optical network (PON) can contain multiple Optical Line
Terminals (OLTs), each connected by a shared optical fiber to a respective
Optical
Distribution Network (ODN) with multiple Optical Network Terminals (ONTs) on
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individual optical fibers. ONTs can malfunction and interfere with
communications
between the ONTs and the OLT on a shared optical fiber. Such malfunctions are
generally the result of power outages or typical communication systems errors
or
failures. Other disruptions in communications can be caused by optical fibers
being
cut, such as by a backhoe. If ONTs are malfunctioning for any other reason;
identifying the issue requires a technician to inspect each ONT, possibly
causing
costly interruptions to service.
SUMMARY OF THE INVENTION
A method or corresponding apparatus for quickly deterrnining a particular
optical network terminal (ONT) is malfunctioning in a passive optical network
(PON) in accordance with an embodiment of the present invention is provided.
An
example embodiment includes: identifying a control ONT from among multiple
ONTs in a passive optical network, the control ONT functioning normally with a
normal, non-data, output signal level; identifying a test ONT from among the
multiple ONTs, the test ONT potentially malfunctioning with an above normal,
non-
data, output signal level; and determining the test ONT is actually
malfunctioning,
as opposed to being a different network fault, such as a line cut or power
outage, by
attempting to range the control ONT and the test ONT and observing both ONTs
fail
to range.
A method for diagnosing problems on a time division multiple access
(TDMA) optical. distribution network (ODN) is provided. A method according to
an
-example embodiment of the invention includes: (i) measuring a no-input signal
power level on a communications path configured to carry upstream
communications between multiple optical network terminals (ONTs) and an
optical
25. line terminal (OLT) in-a passive optical network (PON) at a time no
upstream
communications are on the communications path from the ONTs to the OLT; (ii)
comparing the measured no-input signal power level to a threshold; and (iii)
generating a notification in an event the threshold is exceeded.
A method for ranging an optical network terminal (ONT) in a passive optical
network (PON) is provided. The method according to an example embodiment of
the invention includes: .(i) transmitting a ranging request from an Optical
Line
Terminal (OLT) to an ONT in connection with a transport layer ranging window;
(ii)
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monitoring for a ranging response from the ONT during at least one physical
layer
ranging window within the transport layer ranging window, the transport layer
ranging window having a duration longer than the physical layer ranging
window;
and (iii) determining at least one metric associated with the ranging response
for use
in connection with upstream communications between the ONT and the OLT. The
metric(s), used in connection with upstream communications, are accurately
-determined, and communications faults during normal operations are thus
reduced.
A method or corresponding apparatus for ranging an optical network
terminal (ONT) which is tolerant to a fault condition is provided in
accordance with
an embodiment of the present invention. An example embodiment includes
resetting a receiver of an optical line terminal (OLT) at about a time a
ranging
response from an ONT is expected to be received to tolerate a fault condition
otherwise affecting ranging of the ONT.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing will be apparent from the following more particular
description of example embodiments of the invention, as illustrated in the
accompanying drawings in which like reference characters refer to the same
parts
throughout the different views. The drawings are not necessarily to scale,
emphasis
instead being placed upon illustrating embodiments of the present invention.
FIG. lA is a block diagram of an example passive optical network (PON)
employing embodiments of the present invention;
FIG. I B is a network diagram illustrating an example technique of
determining a control optical network terminal (ONT) and a test ONT in a
network
employing an embodiment of the present invention;
FIG. 1 C is a network diagram illustratirng an example technique of verifying
a test ONT is malfunctioning with an above normal, non-data, output signal;
FIG. 2 is a flow diagram representing the example techniques of FIGS. I B
and 1 C;
FIGS. 3A-3D are network diagrams illustrating a method for identifying
control ONTs and test ONTs;
FIG. 4 is a flow diagram illustrating a method for attempting to range
multiple ONTs together and identifying the ONTs that-fail to range;
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FIG. 5 is a flow diagram illustrating a method for identifying control ONTs;
FIG. 6 is a flow diagram illustrating a method for verifying a control ONT;
FIG. 7 is a flow diagram illustrating a method for identifying a test ONT;
FIGS. 8A - 8J are network diagrams illustrating a method for identifying a
test ONT;
FIGS. 9A - 9C are flow diagrams illustrating a method for identifying a test
ONT;
FIG. 10 is a block diagram illustrating an apparatus for identifying a passive
optical network (PON) fault;
FIG. 11 is a block diagram illustrating a control ONT identification module;
FIG. 12 is a block diagram illustrating a test ONT identification module;
FIG. 13 is a block diagram illustrating a verification module;
FIG. 14 is a block diagram illustrating an optical_line terminal (OLT)
containing a notification generator;
FIG. 15 is a flow diagram illustrating a method for identifying a PON failure
and notifying an operator that an ONT is malfunctioning;
FIG. 16 is block diagram illustrating a PON capable of identifying that a test
ONT is malfunctioning;
FIG. 17 -is a block diagram illustrating a computer-readable medium
containing a sequence of instructions- which enable a processor to identify a
PON
failure;
FIG. 18 is a network diagram of an example PON;
FIG. 19 is a power level diagram illustrating power levels associated with an
input signal and a no-input signal in accordance with example embodiments of
the
invention;
FIG. 20A is block diagram illustrating layer 2 communications established
between an OLT and ONTs in accordance with example embodiments of the
invention;
FIG. 20B is a network block diagram illustrating measuring a no-input
signal power level on an upstream communications path prior to establishing
layer 2
communications between an OLT and an ONT in accordance with example
embodiments of the invention;
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FIG. 20C is a network block diagram illustrating measuring a no-input signal
power level on an upstream communications path after establishing layer 2
communications between an OLT and ONTs in accordance with example
embodiments of the invention;
FIGS. 21 A-21 C are upstrearn communications frames illustrating example
embodiments of measurements of a no-input signal power level on an upstream
communications path being measured during a time there are no upstream
communications;
FIG. 22 is a power level diagram illustrating an extinction ratio and no-input
extinction ratio in accordance with example embodiments of the invention;
FIG. 23A is a power level diagram illustrating an integrated no-input signal
power level ramping over time;
FIG. 23B is a timing diagrarn illustrating anintegrated no-input signal
power level ramping over a ranging window;
FIG. 24A is a block diagram of an example OLT;
FIG. 24B is a block diagram of an example processor supporting example
embodiments of the invention;
FIG. 25A is a flow diagram of an example process performed in accordance
with an example embodiment of the invention;
FIG. 25B is a flow diagram of an example process performed in accordance
with an example embodiment of the invention.
FIG. 26 is a message diagram illustrating a procedure of ranging an ONTT;
FIGS. 27A and 27B are message diagrams illustrating communications from
communicating ONTs halted, and a ranging request and a ranging response
exchanged, during a transport layer ranging window in accordance with an
example
embodiment of the invention;
FIG. 28 is a diagram illustrating lengths of a transport layer ranging window,
physical layer ranging window, and ranging response in accordance with an
example
embodiment of the invention;
FIGS. 29A and 29B are a timing diagram illustrating an integrated no-input
signal power level ramping over a physical layer ranging window in accordance
with example embodirnents of the invention;
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FIG. 30 is a series of timing diagrams illustrating dynamically adjusting a
physical layer ranging window in an iterative manner in accordance with an
example
embodiment of the invention;
FIG. 31 is a series of timing diagrams illustrating shifting a physical layer
5. ranging window within a transport layer ranging window in accordance with
an
example embodiment of the invention;
FIGS. 32A-C are a series of timing diagrams illustrating shifting a physical
layer ranging window incrementally across the transport layer ranging window
in
accordance with an example embodiment of the invention;
FIG. 33 is a timing diagram illustrating shifting a physical layer ranging
window by an amount expected to result in receiving a ranging response in full
in
accordance with an example embodiment of the invention;
FIG. 34 is a timing diagram illustrating lengthening the duration of the
physical layer ranging window in accordance with an example embodiment of the
invention;
FIGS. 35 is a diagram illustrating monitoring for ranging response during a
series of physical layer ranging windows in accordance with an example of
embodiment of the invention;
FIGS. 36A and 36B are diagrams illustrating shifting a series of physical
layer ranging windows by an amount expected to result in receiving a ranging
response in full in accordance with an example embodiment of the invention;
FIG. 37 is a diagram illustrating reducing a physical layer ranging window if
a measured no-input signal power level exceeds a threshold in accordance with
an
example embodiment of the invention;
FIG. 38 is a block diagram of an example optical line terminal (OLT)
supporting example embodiments of the invention;
FIG. 39 is a block diagram of an example monitor unit supporting examples
embodiments of the invention;
FIG. 40 is a flow diagram of an example process performed in accordance
with an example embodiment of the invention;
FIG. 41 is'a flow diagram of an example process performed in accordance
with an example embodiment of the invention;
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FIG. 42 is a flow diagram of another example process performed in
accordance with an example embodiment of the invention.
FIG. 43 is a block diagram of an example system to tolerate a fault condition
otherwise affecting ranging of an ONT in accordance with an embodiment of the
present invention;
FIG.44 is a timing diagram illustrating an integrated no-input signal power
level ramping over a ranging window;
FIG. 45 is a timing diagram illustrating resetting a receiver of an optical
line
terminal (OLT) at about a time a ranging response from an optical network
terminal
(ONT) is expected to be received in accordance with an embodiment of the
present
invention;
FIGS. 46A-46B are timing diagrams illustrating changing a time to reset a
receiver of an OLT by adding and subtracting a delay in accordance with
embodiments. of the present invention;
FIG. 47 is a timing diagram illustrating changing a time to reset a receiver
of
an OLT by delaying for one or more delay incrementsin accordance with an
embodiment of the present invention;
FIGS. 48A-48B are timing diagrams illustrating incrementing a time to reset
a receiver of an OLT with each successive ranging attempt in accordance to an
embodiment of the present invention;
FIG. 49 is a timing diagram illustrating incrementing a time to reset a
receiver of an OLT through a range of delay increments in accordance with an
embodiment of the present invention;
FIG. 50 is a flow chart of an example process ranging an ONT in accordance
with an embodiment of the present invention; and
FIG. 51 is a flow chart of an example process identifying a fault condition in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
A description of example embodiments of the invention follows.
FIG.IA is an example passive optical network (PON) 10 illustrating an
optical line terminal (OLT) 15 in communication with n number of optical
network
terminals (ONTs) 20a, 20b, 20c...20n, via optical communication paths 25and
27a,
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27b, 27c... 27n and an optical splitter/combiner 29. In this example, a first
ONT 20a
is undergoing a ranging procedure, which includes receiving a ranging request
or
grant 30 and responding with a ranging response 35. A second ONT 20b is not
communicating with the OLT 15 during the ranging procedure between the OLT 15
and the first ONT 20a. However, in this example, rather than sending upstream
communications and communicating with the OLT 15, the second ONT 20b is
observed sending a no-input signal 40 - a form of non-communication, which is
an
example of a fault caused by a faulty optical transmitter outputting optical
power
when none should be. As also illustrated, a third ONT through and an nth ONT
20c...20n are communicating and sending upstream communications 45.
A fault in a PON or a PON fault may be detected by comparing a result of
ranging a test ONT, such as the first ONT 20a, with a result of ranging a
control
ONT, in accordance with example embodiments described in reference to FIGS. 1
B-
17. A PON fault may also be detected by measuring a power level associated
with a
no-input signal, such as the no-input signal 40, on an upstream communications
path, in accordance with example embodiments described in reference to FIGS.
18-
25b.
Effects of a PON fault may be minimized by ranging an ONT during a
physical layer ranging window that may be shorter in duration than a transport
layer
ranging window, in accordance with example embodiments described in reference
to
FIGS. 26-42. Effects of a PON fault may also be minimized by resetting a
receiver
or transceiver of an OLT, such as the OLT 15, at about a time a ranging
response
(e.g., the ranging response 35) is expected to be received, in accordance with
example embodiment described in reference to FIGS. 43-51.
FIGS. 1B-17 illustrate example embodiments for detecting a passive Optical
network (PON) fault by comparing or otherwise verifying a result of ranging a
test
optical network terminal (ONT) or otherwise a suspected rogue ONT with a
result of
ranging a control ONT. As used herein, a control ONT is an ONT functioning
normally with a normal, non-data, output signal level. In contrast, a test ONT
is an
ONT that is potentially malfunctioning with an above normal, non-data, output
signal level. A rogue ONT is an ONT that has an optical transmitter that
outputs an
above normal output signal level when not transmitting data. A non-data signal
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level refers to a signal level output by a transmitter in an ONT during a time
period
in which it is not transmitting data (i.e., 1's or 0's) in the upstream
direction, as
illustrated in the example network herein.
Normal, non-data, signal levels are less than -40dBm, such as between -
60dBm and -80dBm. Logical "zero" data signal levels are typically about -5dBm,
and logical "one" data signal levels are typically between about I dBm and
3dBm.
An above-normal, non-data signal level has been observed to be between -35dBm
and -25dBm, but higher levels are also possible. Above-normal, non-data signal
levels are caused by a failure in an optical transmitter and can lead to
upstream
communications errors due to measurements made during a ranging process or as
a
result of the above-normal, non-data levels adversely affecting an optical
receiver
during normal communications. In the ranging process scenario; the measurement
errors may disrupt upstream communications for some or all ONTs communicating
with an optical line terminal (OLT).
When a rogue ONT is present in a passive optical network (PON) it may not
initially appear as a failure depending on the sensitivity of the
corresponding PON
card to detect non-data signals. Additionally, it may not initially affect the
communication of other ONTs with the OLT. The rogue ONT typically causes a
failure in communications when the OLT requests the ONTs in the same optical
distribution network (ODN) as the rogue ONT to range. The above normal, non-
data, output. signal coming from the rogue ONT causes the ONTs on the shared
optical fiber to'fail to range, adversely affecting it own or multiple ONTs'
communications with the OLT. Other times a PON is typically affected by a
rogue
ONT is when a new ONT is added to an ODN and the ONT is a rogue ONT or when
an ONT loses ranging on an ODN containing a rogue ONT.
FIGS. 1 B and 1 C are network diagrams illustrating an example method of
identifying a control ONT and a test ONT and verifying that the test ONT is
actually
malfunctioning (i.e., a rogue ONT) by having an above normal, non-data, output
signal. This example method is referred to herein as a rogue ONT detection
method.
In FIG. 1 B, an OLT 105 is shown containing a control ONT identification
module
110 and a test ONT identification module 115. Each ONT 135a-135e sends non-
data signals 145a-145e and communication signals (not shown) in an upstream
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direction up individual optical fibers 140a - 140e. The signals are combined
at a
splitter/combiner 130, and the combined output 150 is sent to the OLT 105. In
operation, the OLT 105 performs the rogue ONT detection method by first using
the
combined output 150 to determine if the network is rogue affected. If the
network is
rogue affected, then the combined output is used to determine if at least one
control
ONT can be identified using the control ONT identification module I 10. If at
least
one control ONT is identified, the combined output 150 is used to identify a
test
ONT using the test ONT identification module 115. The control ONT
identification
module 110 isolates a control ONT, here illustrated as ONT 135a. The test ONT
identification module 115 isolates a test ONT that is potentially
malfunctioning, here
illustrated as ONT 135c.
The output indicators 145a - 145e represent the output signal levels of the -
respective ONTs 135a - 135e. An ONT with an output indicator of "normal
output"
is an ONT that is functioning normally with a normal, non-data, output signal
level
and can be defined as a control ONT as is ONT 135a. An ONT with an output
indicator of "above normal output," illustrated in this example as ONT 135c,
is
potentially malfunctioning with an above normal, non-data, output signal
level.
Referring to FIG. I C, a verification module 120 in the OLT 105
distinguishes the type of malfunction ONT 135c, the test ONT, is experiencing
by
attempting to range the test ONT 135c with ONT 135a, the control ONT. Ranging
requests 155a and 155c are sent down optical fibers 140a and 140c to range ONT
135a with ONT 135c. The control ONT 135a and the test ONT 135c responsively
send ranging responses 160a and 160c up the optical fibers 140a and 140c to
the
verification module 120. If ONT 135a, the control ONT, is unable to range with
ONT 135c, the test ONT, the verification module 120 confirms the test ONT 135c
is
malfunctioning because of an above normal, non-data, output signal level
rather
than, for example, a power outage, typical communications system errors or
failures,
or a broken optical fiber.
FIG. 2 illustrates a method of identifying a passive optical network (PON)
failure. A control ONT and a test ONT are identified (205, 210) from among the
multiple ONTs. The test ONT is verified (215) as malfunctioning with an above
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normal, non-data, output signal level by attempting to range the control ONT
with
the test ONT and observing both ONTs fail to range.
Before describing details of the generalized description of FIGS '1 B, 1 C and
2 above, an enumerated listing illustrating an embodiment that may be used to
identify an ONT transmitting an above-normal, non-data signal level is
presented.
For purposes of simplifying the enumerated listing, an ONT transmitting an
above-
normal, non data signal level is refeired to as a"rogue ' ONT. The term E-STOP
refers to an emergency stop state that effectively shuts off an ONT
transmitter,
thereby preventing it from sending signals to the OLT.
1. Determine if a PON is affected by a rogue ONT:
a. create a list of existing ONTs in the PON;
b. force all of the ONTs of the PON to un-range then to range;
c. create a list of ONTs that fail to range, if all ONTs range, the
PON is not affected by a rogue ONT;
d. E-STOP all except a first "un-ranged ONT;"
e. attempt to range the first ONT on the list to determine if a rogue
ONT was preventing it from ranging previously in step I c above;
f. if the first un-ranged ONT can now range, label the ONT as a
"control ONT;"
g. since it is possible that the first un-ranged ONT was powered
down and coincidentally was powering up during the ranging
request, check the next un-ranged ONT on the list by E-STOP all
except the second un-ranged ONT. Then attempt to range the
second ONT;
h. if the second ONT can now range, label the ONT as a second
control ONT;
i. the process of identifying control ONTs can either abort after the
first control ONT is identified or continue to identify multiple
control ONTs.
. 2. Isolate the rogue ONT by one of two methods or a blend of the methods:
a. Multi-Rogue Algorithm:
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i. sequence through all the ONTs on the list and attempt to
range each one individually while all other ONTs on the
list are E-STOPed, labeling all ONTs that fail to range as
"test ONTs."
b. Single-Rogue Algorithm:
i. divide the existing ONTs in half, E-STOP one half and
attempt to range the other half, if the other half ranges the
rogue ONT is one of the E-STOPed ONTs;
ii. sequence through dividing the group of ONTs known to
contain the rogue ONT in half and determining which half
contains the rogue ONT. When the size of each half is
one ONT, label the ONT that fails-to range as the "test
ONT."
3. Verify a test ONT is a rogue ONT:
a. sequence through the list of test ONTs, attempting to range all, or
at least a subset of, control ONTs with each test ONT, while all
other ONTs are E-STOPed. Those test ONTs that prevent all (or
at least the subset of) control ONTs from ranging are further
verified in the next step. Those that do not prevent the control
ONTs from ranging are removed from the test ONT list;
b. to further verify the test ONTs, E-STOP all existing ONTs except
the control ONTs. Wait for the control ONTs to range. Check if
all (or at least the subset of) the control ONTs are ranged. If the
control ONTs range with the test ONTs in E-STOP, the test
ONTs are rogue ONTs, and the and the verification process has
eliminated broken optical fibers, power-outages, and typical
communications systems errors or failures as the cause of the
malfunction in the PON.
4. Present a list of verified rogue ONTs to an 6perator.
FIGS. 3A - 3D are network diagrams illustrating identifying a method for
identifying control ONTs and test ONTs. In FIG 3A, an OLT 340 sends ranging
requests 310a-310c down shared optical fibers 315a - 315c to
splitter/combiners
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320a - 320c. The splitter/combiners 320a - 320c send the ranging requests down
the individual communications paths 325a - 325o to ONTs 305a - 305o. The ONTs
305a - 305o send ranging responses 330a - 330c back to the OLT 340. In this
illustration, the ONTs 305f - 305j are identified as failing to range.
Referring to FIG. 3B, the OLT (not shown) sends a signal 311b, such as an
E-Stop ON or E-Stop OFF signal, to disable or enable the outputs of theONTs
305f
- 305j down the shared optical fiber 315b to the splitter/combiner 320b,
which, in
turn, directs the signal 311b to the ONTs 305f- 305j. The indicators 335f-
335j
above respective communications paths 325f- 325j illustrate that the output of
ONTs 305f - 305j are disabled.
In FIG. 3C, the OLT (not shown) sends another ranging request signal 310b
to each ONT 305f- 305j individually and receives back a ranging response
signal
330b indicating whether the ONTs 305f- 305j are able to range individually.
Between each ranging request signal 310b, the OLT sends a signal 3 l 1 b (not
shown)
enabling and disabling the outputs of the ONTs 305f - 305j in turn, such that
only
the output of the ONT to be ranged is enabled. The indicators 335f - 335j
illustrate
the status of the outputs of ONTs 305f - 305j for each ranging request.
Referring to FIG. 3D, the ONTs 305f, 305g. 305i, and 305j are illustrated as
having ranged and may be defined as control ONTs. The ONT 305h in this example
is illustrated as having failed to range and is defined as a test ONT.
FIG. 4 is a flow diagram 400 illustrating a method for attempting to range
the multiple ONTs of the PON together and determining which ONTs fail to
range.
After the flow diagram starts (405), an attempt is made to range the multiple
ONTs
of the PON (410). Cycling through each ONT in the PON (415), the ONT is
checked to determine if it ranges (420). If the ONT fails to range, it is
added to a list
of ONTs that fail to range (425). If the ONT ranges, it is not a control ONT
or a test
ONT, and the ONT is ignored. If the ONT being checked is the last ONT in the
PON (430), the flow diagram 400 exits to the methods shown in FIGS. 5-7.
FIG. 5 is a flow diagram 500 illustrating a method to determine a control
ONT. After a list has been made of the ONTs that fail to range by the method
shown in FIG. 4; the outputs of the ONTs on the list are disabled (505).
Starting
with the first ONT on the list (510), the output of the ONT is enabled (515),
and an
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attempt is made to range the ONT individually (520). If the ONT ranges (525),
the
ONT is a control ONT (530). Optionally, the cycle can exit after the first
control
ONT is determined (535). If the ONT does not range or more then one control
ONT
is needed, a check is made if, optionally, the ONT is the last ONT on the list
(540)
or if a condition is met (540). Such a condition includes at least one of the
following: a time limit, a specified number of control ONTs have been
identified, a
percentage of the multiple ONTs are determined to be control ONTs, a
percentage of
the ONTs that failed to range are determined to be control ONTs, and a stop
command from an operator is received. If the ONT is not the last ONT on the
list
or, optionally, the condition is not met, the.cycle repeats from 505 through
540. If
the ONT is the last on the list or the condition is met, the cycle is complete
and flow
diagram 500 exits (545).
FIG. 6 is a flow diagram 600 illustrating a method to verify an ONT is
properly labelled as a control ONT. It is possible that the ONT identified as
the
control ONT is actually a test ONT, has a broken optical fiber, or was powered
down and coincidentally powered up during the ranging request: Therefore,
after a
list has been made of the ONTs that fail to range by the method shown in FIG.
4, the
outputs of the ONTs on the list are disabled (605). Where "z" represents an
ONT on
the list, starting with the first ONT on the list (610), the output-of the ONT
is
enabled (615) and an attempt is made to range the ONT individually (620). If
the
ONT ranges (625), a check is made to see if the previous ONT on the list was
able to
range individually (630). If yes, the ONT is verified as a control ONT (635)
and the
flow diagram-600 exits (640). If the ONT either fails to range individually
(625) or
the previous ONT on the list failed to range, a check is made if the current
ONT is
the last ONT on the list (645). If yes, the cycle is complete and flow diagram
600
exits (650). If no, the cycle is repeats from 605 through 645.
In another embodiment, after the outputs of the ONTs on the list are disabled
(605), verifying an ONT is properly labelled as a control ONT optionally
includes
cycling through the ONTs of the multiple ONTs. Where "z" represents an ONT of
the multiple ONTs, starting with the first ONT of the multiple ONTs (610), the
output of the ONT is enabled (615) and an attempt is made to range the ONT
individually (620). If the ONT ranges (625), a check is made to see if the ONT
is on
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the list of ONTs that failed to range and the ONT is at least the second ONT
of the
multiple ONTs (630). If yes, the ONT is verified as a control ONT (635) and
the
flow diagram 600 exits (640). If the ONT either fails to range individually
(625) or
the ONT is not on the list of ONTs that failed to range and/or is not at least
the
second ONT of the multiple ONTs (630), a check is made if the current ONT is
the
last ONT of the multiple ONTs (645). If yes, the cycle is complete and flow
diagram 600 exits (650). If no, the cycle is repeats from 605 through 645.
FIG. 7 is a flow diagram 700 illustrating a method for identifying a test
ONT. After a list has been made of the ONTs that fail to range by the method
shown
in FIG. 4, the outputs of the ONTs on the list are disabled (705). Starting
with the
first ONT on the list (710), the output of the ONT is enabled (715) and an
attempt is
made to range the ONT individually (720). If the ONT fails to range (725), the
ONT is a test ONT (730). If the ONT ranges or after it has been identified as
a test
ONT, the ONT is checked to determine if it is the last ONT on the list (730).
If yes,
all test ONTs have been identified and flow diagram 700 exits (740). If no,
the
cycle repeats from 705 through 735.
FIGS. 8A - 8J are network diagrams illustrating another method for
identifying a test ONT when only one test ONT exists. Referring to FIG. 8A,
the
multiple ONTs of a PON are divided into a group 1(805), illustrated as ONTs
815a
and 815b, and a group 2(810), illustrated as ONTs 815c-815e. An OLT (not
shown) sends a signal 820 to disable the outputs of the ONTs down a shared
optical
fiber 821, through a splitter/combiner 825, and down the individual
communication
paths 830a - 830e to the ONTs 815a - 815e. The indicators 835a-835e above the
respective communication paths 830a - 830e illustrate the outputs of ONTs 815a
-
815e are disabled.
In FIG. 8B, the OLT (not shown) sends a signal 822 to enable the outputs of
the ONTs of group 1 (805). The indicators 835a and 835b illustrate the outputs
of
ONTs 815a.and 815b are enabled. Referring to F1G. 8C, the OLT (not shown)
sends
a ranging request signal 823 to group 1 (805). The ONTs, 815a and 815b, of
group 1
(805) send ranging response signals 840a and 840b back confirming whether they
range. In this illustration, all of the ONTs in group 1 (805) successfully
range,
indicating the test ONT is in group 2(810).
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In FIG. 8D, group 2 (810) of FIG. 8C, known to contain the test ONT, is
divided into two new groups, group 1' (806), illustrated as being ONT 815c,
and
group 2' (811), illustrated as being ONTs 815d and 815e. The OLT (not shown)
sends a signal 820 to disable the outputs of all the ONTs. The indicators 835a
-
835e illustrate the outputs of ONTs 815a - 815e are disabled. Referring to
FIG. 8E,
the OLT (not shown) sends a signal 822 to enable the output of the ONT of
group 1'
(806). The indicator 835c illustrates the output of ONT 815c is enabled. In
FIG. 8F,
the OLT (not shown) sends a ranging request signal 823 to the ONT of group I'
(806). ONT 815c sends back ranging response signal 840c confirming whether it
ranges. In this illustration, group 1' (806) fails to range and, therefore,
contains a
test ONT. To verify that there is not a test ONT in group 2' (811) as well;
group 2'
(811) is also ranged.
In FIG. 8G, the OLT (not shown) sends a signal 820 to disable the outputs of
the ONTs. The indicators 835a - 835e illustrate the outputs of ONTs 815a -
815e
are disabled. Referring to FIG. 8H, the OLT (not shown) sends a signal 822 to
enable the outputs of group 2' (811). The indicators 835d and 835e illustrate
the
outputs of the ONTs of group 2' (811) are enabled. In FIG. 81, the OLT sends
ranging request signal 823 to the ONTs of group 2' (811). The ONTs 815d and
815c of group 2' (811) send ranging response signals 840d and 840e back
confirming whether they range. = In this illustration, group 2' (811)
successfully
ranges indicating that group 1' (806) contains the test ONT. As shown in FIG.
8J,
group V (806) contains only one ONT, ONT 815c. Therefore, ONT 815c is the test
ONT.
FIGS. 9A - 9C are flow diagrams illustrating a method for identifying a test
ONT as outlined in network diagrams FIGS. 8A - 8J. Group I and group 2 are
defined from the multiple ONTs of the PON (902). The outputs of all the ONTs
are
disabled (903). Starting with the first group (904), the output of the group
is enabled
and an attempt is made to range the ONTs in the group (905). If the ONTS of
the
group successfully range (906), the other group contains the test ONT (907).
If the
number of ONTs in the group containing the test ONT is one (908), the ONT of
that
group is the test ONT (909), and the cycle is completed (910). If the group
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containing the test ONT has more then one ONT (908), that group is divided
into a
new group 1 and group 2 (911). The cycle repeats from 903 through 906.
If the ONTs of the group fail to range (906), a check is made if the group is
group 2 (912). If the group is not, the cycle repeats from 903 through 906. If
the
group is group 2, then multiple test ONTs exist (913) and the method
illustrated in
FIG. 9B is used to identify the test ONTs. Referring to FIG. 9B, an attempt is
made
to range the multiple ONTs of the PON (914). Cycling through each ONT in the
PON (915), the ONT is checked to determine if it ranges (916). If the ONT
fails to
range, it is added to a list of ONTs that fail to range (917). lf the ONT does
range, it
is not a test ONT and is ignored. If the ONT being checked is the last.ONT in
the
PON (918), the process exits to the method shown in FIG. 9C.
In FIG. 9C, the outputs of the ONTs on the list are disabled (919). Starting
with the first ONT on the list (920), the output of the ONT is enabled (921),
and an
attempt is made to range the ONT individually (922). If the ONT fails to range
(923), the ONT is defined as a test ONT (924). If the ONT ranges or after it
has
been identified as a test ONT, the ONT is checked to determine if it is the
last ONT
on the list (925). If yes, all test ONTs are identified and the cycle is
complete (926).
If no, the cycle repeats from 919 through 925.
FIG. 10 is a block diagram illustrating an apparatus for identifying a PON
fault. An optical line terminal (OLT) 1005 includes a control ONT
identification
module 1010, a test ONT identification module 1015, and a verification module
1020. Reference number 1, 2, and 3 show a first, second, and third
communication
made with ONTs 1030a-1030n. The control ONT identification module 1010,.the
test ONT identification module 1015, and the verification module 1020 in turn
send
a signal 1021 which includes a ranging request to the splitter/combiner 1025
and on
to the individual ONTs 1030a-1030n. The ONTs 1030a-1030n send a ranging
response signal 1022 back to the OLT 1005 indicating their ranging response.
The
control ONT identification module 1010 monitors the multiple ONTs and
identifies
control ONTs. Similarly, the test ONT identification module 1015 monitors the
multiple ONTs and identifies test ONTs. The verification module 1020 is
configured to determine that the test ONT is actually malfunctioning due to
having
an above normal, non-data, output signal by ranging the control ONT with the
test
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ONT.and observing both ONTs fail to range when the test ONT has its output
enabled, and also observing the control ONT successfully ranges when that same
test ONT has its output disabled.
FIG. 11 is a block diagram illustrating a control ONT identification module
1105.. The control ONT identification module 1105 includes a ranging unit
1110, an
enabling/disabling unit 1115, and a logic unit 1120. The ranging unit 1110 and
the
logic unit 1120 are in conununication with one another. Optionally, the
enabling/disabling unit 1 115 is in communication the ranging unit 1110 and/or
the
logic unit 1120. The enabling/disabling unit 1115.sends signals to the ONTs
(not
shown) to either enable or disable their outputs, while the ranging unit 1110
sends
signals to attempt to range to the ONTs. The logic unit 1120 identifies ONTs
that
successfully range individually as control ONTs.
In addition, the control identification module 1105 can optionally include a
verification unit 1125 and/or limiting unit 1130, both in communication with
the
logic unit 1120. The verification unit 1125 verifies a control ONT identified
by the
logic unit 1120 is not actually a test ONT, does not have a broken optical
fiber, and
was not powered down and coincidentally powering up at the time it was
identified
as a control ONT. The limiting unit 1130 stops the logic unit 1120 from
identifying
control ONTs when a specified condition has been met. The condition includes
at
least one of the following: a time limit, a specified number of control ONTs
are
determined, a percentage of the multiple ONTs are determined to be control
ONTs,
a percentage of the ONTs that failed to range are determined to be control
ONTs,
and a stop command from an operator is received.
FIG. 12 is a block diagram illustrating a test ONT identification module
1205. The test ONT identification module 1205 includes a ranging unit 1215,
enabling/disabling unit 1220, and a logic unit 1225. The ranging unit 1215 and
the
logic unit 1225 are in communication with one another. Optionally, the
enabling/disabling unit 1220 is in communication with the ranging unit 1215
and/or
the logic unit 1225. The enablirig/disabling unit 1220 sends signals to the
ONTs
(not shown) to either enable or disable their outputs, while the ranging unit
1215
sends signals to attempt to range to the ONTs. The logic unit 1225 identifies
ONTs
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-that fail to range individually as test ONTs or, optionally, identifies a
group of ONTs
that fail to range as containing a test ONT.
In addition, the test ONT identification module 1205 can optionally include a
dividing unit 1210, a test ONT unit 1235, a verification unit 1230, and a
switch unit
1240. The test ONT unit 1235 is in communication with the logic unit 1225 and
the
dividing unit 1210. The verification unit 1230 is in communication with the
logic
unit 1225 and switch unit 1240. The dividing unit 1210 defines- two groups of
ONTs. The test ONT unit 1235 conununicates with the dividing unit 1210 to
divide
a group_identified as containing a test ONT by the logic unit 1225 into two
new
groups and has the logic unit 1225 identify which of the new groups of ONTs
fail to
range. The vcrification unit .1230 checks whether only one group contains a
test
ONT. If the verification unit 1230 determines that both groups contain a test
ONT,
the verification unit 1230 notifies the switch unit 1240. The switch unit 1240
then
sends a signal to the test ONT unit 1235 to attempt to range the ONTs
individually
and to identify ONTs that fail to range as test ONTs.
FIG. 13 is a block diagram illustrating a verification module 1305. The
verification module 1305 includes a ranging unit 1310, an enabling/disabling
unit
1315, a logic unit 1320, and a verification unit 1325. The ranging unit 1310
and the
logic unit 1320 are in conununication with one another. Optionally, the
enabling/disabling unit 1315 is in communication with the ranging unit 1310
and/or
the logic unit 1320. The verification unit 1325 is in communication with the
logic
unit 1320.
Once the control ONT identification module (not shown) identifies a control
ONT'and the test ONT identification module (not shown) identifies a test ONT,
the
enabling/disabling unit 1315 sends signals to the ONTs (not shown) either to
enable
or disable their outputs. The ranging unit 1310 then sends a signal to attempt
to
range the control ONT with the test ONT. The logic unit 1320 identifies
whether
the test ONT and control ONT range. If not, the verification unit 1325
confirms that
the test ONT is malfunctioning by sending an above normal, non-data, output
signal
level rather than from a power outage, broken optical fiber, or typical
communications systems errors or failures.
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FIG. 14 is a block diagram illustrating an OLT 1405 including a control
ONT identification module 1410, a test ONT identification module 1415, a
verification module 1420, and an optional- notification generator 1425 in
communication with the verification module 1420. Reference number 1, 2, and 3
show a first, second, and third communication made with the ONTs 1435a-1435n.
The control ONT identification module 1410, the test ONT identification module
1415, and the verification module 1420'in turn send a ranging request signal
1426 to
the splitter/combiner 1430 and on to the individual ONTs 1435a-1435n. The ONTs
1435a-1435n send a ranging response signal 1427 back to the OLT 1405
indicating
their ranging response. The control ONT identification module 1410 monitors
the
ONTs 1435a - 1435n and identifies control ONTs. Similarly, the test ONT
identification module 1415 monitors the ONTs 1435a - 1435n and identifies test
ONTs. The verification module 1420 ranges a control ONT with a test ONT and,
if
both fail to range, confirms the test ONT is malfunctioning by outputting an
above
normal, non-data, output signal. The notification generator 1425 generates a
notification that an ONT is malfunctioning.
FIG. 15 is a flow diagram illustrating a method identifying a PON failure and
notifying an operator that a test ONT is malfunctioning. A control ONT and a
test
ONT are identified (1505 and 1510) from among multiple ONTs in a passive
optical
network. The test ONT is verified (1515) as malfunctioning with an above
normal,
non-data, output signal by attempting to range the control ONT identified in
1505
with the test ONT identified in 1510 and observing both ONTs fail to range.
Lastly,
an operator is notified that a test ONT is malfunctioning (1520).
FIG. 16 is block diagram illustrating a PON 1640 capable of identifying that
a test ONT is malfunctioning. Each OLT 1605 includes a control ONT
identification module 1610, a test ONT identification module 1615, a
verification
module 1620, and an optional notification generator 1635 in communication with
the verification module 1620. For each OLT 1605, reference numbers 1, 2, and 3
show a first, second, and third communication made with the ONTs 1630a-1630n.
The control ONT identification module 1610, the test ONT identification module
1615, and the verification module 1620 in turn send a ranging request signal
1621 to
the splitter/combiner 1625 and on to the individual ONTs 1630a-1630n. The ONTs
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1630a-1630n send "the ranging response signal 1622 back to the OLT 1605
indicating their ranging response.
The control ONT identification module 1610 monitors the ONTs l 630a -
1630n and identifies control ONTs. Similarly, the test ONT identification
module
1615 monitors the ONTs 1630a - 1630n and identifies test ONTs. The
verification
module 1620 determines the test ONT is malfunctioning with an above normal,
non-
data, signal level by ranging a control ONT with a test ONT and observing both
ONTs fail to range. The notification generator 1635 generates a notification
that an
ONT is malfunctioning.
Optionally, a malfunctioning ONT signal 1645, indicating an ONT is
malfunctioning with an above normal,. non- data, signal level, is sent from a
notification generator in a PON 1640 to a network management server 1650. The
network management server 1650 is in communication with a service provider
1655
and can send an alert 1651 to a service provider 1655. Altematively, a service
provider 1655 can send a query 1652 to the network management server 1650 to
determine if a malfunctioning ONT signal 1645 has been received from the PON
1640. Optionally, a malfunctioning ONT signal 1660 can be sent to an ONT where
it will be received by, for example, a service operator, a client, and/or a
communication device such as a local area network or a computer.
FIG. 17 is a block diagram illustrating a computer-readable medium 1720
containing a sequence of instructions which identify a PON failure. The
instructions
include identifying a control ONT (.1705) and identifying a test ONT (1710)
from
among multiple ONTs in a passive optical network. Lastly, an instruction
verifies
the test ONT (1715) as actually malfunctioning with an above normal, non-data,
output signal by attempting to range the control ONT identified in 1705 with
the test
ONT identified in 1710 and observing both ONTs fail to range.
<</summary of 2090-001 The above description referring to FIGS. 1-17
describes determining a particular optical network terminal (ONT) in a passive
optical network (PON) is malfunctioning by sending a continuous stream of
light up
a shared fiber, which results in adversely affecting conununications between
the
ONT and an optical line terminal (OLT). An example embodiment verifies the
failure is due to a faulty optical transmitter in the ONT and not a different
network
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fault, such as a fiber optic line cut or power outage. Through the use of the
example
embodiment, a service provider can determine in an automated manner which
specific ONT of a PON is malfunctioning.
To understand the problem furiher, greater details of the operations of a
passive optical network (PON), including an optical receiver in an OLT, are
discussed in reference to FIGS. 18-25B.
FIGS. 18-25B illustrate example embodiments of an aspect of the present
invention in which a malfunctioning ONT is detected by looking for a presence
of a
.modulated or unmodulated upstream optical signal when no signal should be
present
on an upstream communications path. Further illustrated is a manner for
determining a malfunctioning ONT by looking for an inappropriate presence of -
unmodulated or very low level modulated upstream optical signal when no signal
should be present on the upstream communications path.
An optical network terminal (ONT) can malfunction in such a way that it
sends a continuous stream of light (e.g., low level, such as less than 10dBm)
up to a
shared fiber of an optical distribution network (ODN). This can adversely
affect
communications between ONTs on the ODN and an optical line terminal (OLT).
Using existing error detection techniques, such as those described in various
passive
optical network (PON) protocols, this type of ONT malfunction may not be
detected. Even if it is detected (e.g., resulting from system failure), the
ONT
malfunction (i.e., output of continuous light at a low level) may not be
identified,.
and field service engineers may spend a great deal of time inspecting a
receiver in
the OLT, -fiber optic cables between the ONTs and OLT, and any relays or
junctions
between the ONTs and OLT. Moreover, the amount of continuously outputted light
which can cause communications errors has been found to be very -low. So,
unless
field service engineers are sensitive to the source of the communications
errors,
hours of lost network services can result.
Detection of an ONT sending a low level continuous stream of light up to a
shared fiber of an ODN may be done several ways. One method may involve
individually disconnecting ONTs from the ODN to determine if there is a single
ONT or multiple ONTs causing the problem. With 'this method, however, the
problem may not be -corrected in a timely fashion. Additionally, this method
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requires considerable customer downtime. In another method, the OLT may be
disconnected from the ODN, and the ODN may be examined with additional test
equipment.
Accordingly, what is needed is a method or corresponding apparatus for
diagnosing.problems on an ODN which detects, prior to establishing layer 2
conununications, a malfunctioning ONT by looking for an inappropriate presence
of
a modulated or unmodulated upstream optical signal when no signal should be
present on the upstream communications path. Furthermore, after. establishing
layer
2 communications with any number of ONTs, a malfunctioning ONT may be
detected by looking for an inappropriate presence of an unmodulated or very
low
level modulated upstream optical signal when no signal should be .present on
the
upstream communications path.
As used herein, a modulated upstream optical signal is a signal which
conveys information (i.e., communicates upstream communications data) and is
interchangeably referre.d to herein as an "input signal"). The input signal
may be
either a "zero-bit input signal" (i.e., communicates a zero-bit) or a "one-bit
input
signal," i.e., communicates a one-bit. In contrast, an unmodulated upstream
optical
signal is a signal-which does not convey information (i.e., communicates no
upstream communications data) and is interchangeably referred to herein as a
"no-
input signal."
Further, power levels associated with a zero-bit input signal or a one-bit
input signal are referred to herein as a "zero-bit input signal power level"
or a "one-
bit input signal power level," respectively. Additionally, a power level
associated
with a no-input signal is referred to herein as a"no-input signal power
level."
In a PON system; multiple ONTs transmit data to an OLT using a common
optical wavelength and fiber optic media. Field experience has derrionstrated
that a
malfunctioning ONT can send an optical signal up to the OLT at inappropriate
times, resulting in the OLT not being able to communicate with any of the ONTs
on
the ODN. A typical PON protocol provides some functionality for detecting this
problem, but is limited only to inappropriate modulated signals. Consequently,
the
following ONT malfunctions are not being detected.
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An example ONT malfunction not being detected involves an ONT sending a
continuous upstream signal (mo(lulated or unmodulated) up the fiber prior to
attempting to establish communications with an OLT on an ODN. Another example
ONT malfunction occurs when an ONT sends an unmodulated light signal up the
fiber at an inappropriate time while attempting to establish communications or
after
having established communications with an OLT on an ODN. Consequently, an
ability to detect whether a.network contains an ONT with such a malfunction
may
depend on an ability to detect an unmodulated light signal.
While an OLT must be able to detect the presence of a modulated signal (or
an input signal) in order to function as a node in a communications path, the
ability
to detect an unmodulated signal (or a no-input signal), however, is not
required for
operation. In accordance with example embodiments of the invention, the
ability to
detect an unmodulated upstream signal may improve the ability of the OLT to
detect
error conditions in upstream communications between ONTs and the OLT, as
discussed hereinafter.
As such, in part, a difference between detecting a modulated versus an
unmodulated upstream signal is that an optical receiver (or transceiver) does
not
have the ability to detect an unmodulated signal. In some cases, the optical
receiver
may not be able to detect or communicate the presence of an unmodulated
upstream
signal.
In other cases, even though the presence of an unmodulated signal may
indicate a system problem,.the presence of an unmodulated signal may not
actually
result in a problem in upstream communications between ONTs and an OLT.
Sometimes the presence of an unmodulated upstream signal is removed by signal
conditioning circuitry on the optical receiver (or transceiver). The
unmodulated
upstream signal adds a "directed current (DC) offset" to a modulated upstream
signal. The DC offset may be subsequently removed from the modulated upstream
signal without corrupting it. Current experience, however, indicates that the
effect
of an unmodulated upstream signal on a modulated upstream- signal varies from
optical receiver to optical receiver. Additionally, the effect of the
unmodulated
upstream signal depends on the brightness or amplitude of the unmodulated
upstream signal.
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FIG. 18 is a network diagram. of an example passive optical network (PON)
1801. The PON 1801 includes an optical line terminal (OLT) 1802, wavelength
division multiplexers 1803a-n,_optical distribution network (ODN) devices
1804a-n,
ODN device splitters (e.g., 1805a-n associated with ODN device 1804a), optical
network terminals (ONTs) (e.g., 1806-n corresponding to ODN device splitters
1805a-n), and customer premises equipment (e.g., 1810). The OLT 1802 includes
PON cards 1820a-n, each of which provides an optical feed (1821 a-n) to ODN
devices 1804a-n: Optical feed 1821 a, for example, is distributed through
corresponding ODN device 1804a by separate ODN device splitters 1805a-n to
respective ONTs 1806a-n in order to provide communications to and from
customer
premises equipment 1810.
The PON 1801 may be deployed for fiber-to-the-business (FTTB), fiber-to-
the-curb (FTTC), and fiber-to-the-home (FTTH) applications. The optical feeds
1821 a-n in PON 1801 may operate at bandwidths such as 155 Mb/sec, 622 Mb/sec,
1.25 Gb/sec, and 2.5 Gb/sec or any other desired bandwidth implementations.
The
PON 1801 may incorporate asynchronous transfer mode (ATM) communications,
broadband services such as Ethemet access and video distribution, Ethernet
point-to-
multipoint topologies, and native communications of data and time division
multiplex (TDM) formats. Customer premises equipment (e.g., 1810) which can
receive and provide communications in the PON 1801 may include standard
telephones (e.g., Public Switched Telephone Network (PSTN)), Internet Protocol
telephones, Ethernet units, video devices (e.g., 1811), computer terminals
(e.g.,
1812), digital subscriber line connections, cable modems, wireless access, as
well as
any other conventional device.
A PON 1801 includes one or more different types of ONTs (e.g., 1806a-n).
Each ONT 1806a-n, for example, communicates with an ODN device 1804a through
associated ODN device splitters 1805a-n. Each ODN device 1804a-n in turn
communicates with an associated PON card l 820a-n through respective
wavelength
division multiplexers I 803a-n. Wavelength division multiplexers 1803a-n are
optional components which are used when video services are provided.
Communications between the ODN devices 1804a-n and the OLT 1802 occur over a
downstream wavelength and an upstream wavelength. The downstream
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communications from the OLT 1802 to the ODN devices 1804a-n may be provided
at 622 megabytes per second, which is shared across all ONTs connected to the
ODN devices 1804a-n. The upstream communications from the ODN devices
1804a-n to the PON cards 1820a-n may be provided at 155 megabytes per second,
which is shared among all ONTs connected to ODN devices 1804a-n.
Error conditions in upstream communications between an optical line
terminal (OLT) and optical network terminals (ONTs) often result in layer 2
communication errors, for example, errors in ranging or normalization
parameters.
One such error condition in upstream communications is the presence of an
unmodulated signal (or a no-input signal) on an upstream communications path..
An
example solution to this problem may include detecting the presence of an
unmodulated signal on the upstream communications path; identifying whether
the
detected unmodulated signal leads to a layer 2 communications error, and
communicating the error condition so that it may be corrected. An unmodulated
signal on the upstream communications path may be detected by measuring a
power
level associated with the unmodulated signal. For the sake of readability, the
power
level associated with the unmodulated signal is referred to herein as a "no-
input
signal power level" and is used throughout this disclosure.
FIG. 19 illustrates three power levels: a minimum logical one input signal
power level 1920, a maximum logical zero input signal power level 1925, and a
maximum no-input signal power level 1930. The terms logical one and logical
zero
are interchangeably referred to herein as a one-bit and a zero-bit.
In general, when the power level of an input signal is above the minimum
logical one input signal power level 1920, the input signal is designated as a
logical
one input signal. When the power level of an input signal is below the maximum
logical zero input signal power level 1925, the input.signal is designated as
a logical
zero input signal. When the power level of an input is below the minimum
logical
one input signal power level 1920 but above the maximum logical zero input
signal
power level 1925, the input signal is indeterminate, i.e., the input signal is
neither a
logical one input signal nor is the input signal a logical zero input signal.
In this way, by modulating or otherwise changing the power level of an input
signal, the input signal can either convey a logical one input signal or a
logical zero
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input signal. Moreover, by modulating the power level of an input signal, the
input
signal conveys information. Accordingly, upstream communications between an
ONT and OLT on an upstream communications pathway is accomplished by
modulating the power level of an input signal to an optical transmitter
generating
.5 optical signals.
In contrast, when the power level of a signal is not modulated, the signal
conveys no information. This is the case when there are no upstream
communications between an ONT and an OLT on an upstream communications
pathway. In this disclosure, the term no-input signal is used to describe a
signal
whose power level is not modulated. Furthermore, the terms unmodulated signal
and no-input signal are used interchangeably throughout this disclosure.
When the power level of a no-input signal is below the maximum no-input
signal power level 1930, a no-input signal is said to be valid or non-faulty.
More
specifically, a no-input signal with a power level less than the maximum no-
input
signal power level 1930 does not or is less likely to cause an error
condition. On the
other hand, when the power level of a no-input signal is above the maximum no-
input signal power level 1930, the no-input signal is said to be invalid or
faulty. In
contrast to a no-input signal with a power level less than the maximum no-
input
signal power level. 1930, a no-input signal with a power level greater than
the
maximum no-input signal power level 1930 does or is more likely to cause an
error
condition (described later in greater detail).
Still referring to FIG. 19, consider the following illustrative example. The
minimum logical one input signal power level 1920 is +3dBm (decibel-
milliwatt),
the maximum logical zero input signal power level 1925 is -5dBm, and the
maximum no-input signal power level 1930 is -40dBm. -
An input signal 1932 with a series of power levels 1935 is received during a
grant timeslot 1940. During the grant timeslot 1940, the input signal 1932 has
power levels which at times are greater than +3dBm and at times are less than -
5dBm. -Thus, the series of power levels 1935 in the input signal 1932
designates -a
series of logical ones and logical zeros. Before the grant timeslot 1940, a
first no-
input signal portion 1945a of the input signal 1932 has a power level less
than -
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40dBm. As such, the first no-input signal portion 1945a of the input signal
1932 is
not faulty, i.e., validly conveys no information.
In contrast, after the grant timeslot 1940, a second no-input signal portion
1945b of the input signal 1932 has a power level greater than -40dBm, e.g_, a
"faulty
no-input signal level" 1950. In this case, the second no-input signal portion
1945b
of the input.signal 1932 is faulty, i.e., invalidly conveys no information.
Discussed
later in greater detail, a no-input signal having a power level, such as the
faulty no-
input signal power level 1.950; may lead to problems in upstream
communications,
e.g., errors in ranging and normalization parameters.
FIG. 20A illustrates upstream communications between an OLT 2005 and
communicating ONTs 2010a-n over an upstream communications path 2015.
Upstream communications begins when the communicating ONTs 2010a-n transmit
upstream coinmunications data 2020a-n on the upstream communications path
2015.
Upstream communications data 2020a-n are then combined on the upstream
communications path 2015 by a splitter/multiplexer 2025. Upstream
communications data 2020a-n are transmitted by the communicating ONTs 2010a-n
at respective predefined times and in the case of a time division multiplexing
(TDM)
communications protocol, placed into individual timeslots 2030a-n of an
upstream
communications frame 2035.
The OLT 2005, via the upstream communications path 2015, receives the
upstream communications frame 2035. The OLT 2005 may then demultiplex (i.e.,
separate) the upstream communications frame 2035 into individual timeslots
2030a-
n. As a result, the OLT 2005 receives respective upstream communications data
2020a-n froin each communicating ONT 2010a-n.
FIG. 20B is a network block diagram illustrating how an OLT 2005 may
measure a power level of a no-input signal (or a no-input signal power level)
on an
upstream communications path 2015 at a time there are no upstream
communications between the OLT 2005 and communicating ONTs 2010a-n. The
no-input signal power level on the upstream communications path 2015 may be
measured at a time the OLT 2005 is ranging an ONT 2011 or at another time
there
are no upstream communications on the upstream communications path 2015, e.g.,
when the OLT 2005 is immediately rebooted and before any ONTs are ranged.
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In an example embodiment, the OLT 2005 may instruct all communicating
ONTs 2010a-n to halt upstream communications in order to range the ONT 2011.
With upstream communications from the communicating ONTs 2010a-n halted, the
no-input sigrial power level on the upstream communications path 2015 should
be
small, (e.g., a power level below the maximum no-input signal power level 1930
of
FIG. 19) or have no value. Typically, once halted, any power present on the
upstream communications path 2015 is caused by, for example, very low level
leakage of optical transmitters (e.g., laser diodes) in transmitter units of
the
communicating ONTs 2010a-n or due to typical optical noise developed or
imparted
onto the upstream communications path 2015.
The OLT 2005 may send the ONT 2011 a ranging request 2040. The ONT
2011, in turn, may respond with a ranging response 2045. During the ranging,
the
no-input signal power level on the upstream communications path 2015 is
measured
during period(s) the ranging response 2045 is not on the upstream
communications
path 2015. As such, the no-input signal power level is not increased by a
signal
representing the ranging response 2045. If the no-input signal power level is
greater
than, for example, the maximum no-input signal power level 1930 of FIG. 19,
the
ONT 2011 is faulty.
The ranging exchange between the OLT 2005 and the ONT 2011 may occur
over a period of time known as a ranging window (not shown, but discussed
below
in reference to FIG. 23B). The measured no-input signal power level on the
upstream communications path 2015 may be averaged over an un-allocated grant
window (not shown). In addition to measuring a no-input signal power level
during
the un-allocated grant window, a no-input signal power level may also be
measured
before any ONTs have been ranged, e.g., when the OLT 2005 is rebooted.
'FIG. 20C is a network block diagram in which upstream communications
between an OLT 2005 and communicating ONTs 2010a-n are carried over an
upstream communications path 2015 . In addition to the communicating ONTs
2010a-n, there is a non-communicating ONT 2013. Upstream communications
begin with the communicating ONTs 2010a-n sending upstream communications
data 2020a-n via the upstream communications path 2015. The non-communicating
ONT 2013 may have no-data to send. Consequently, rather than sending upstream
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communications data 2020, nothing is sent, denoted by a "no-data" indicator
2023.
For purposes of explaining aspects of the invention, the "no-data" indicator
2023
indicates a timeslot portion that is neither filled with an "idle" signal or a
substantive
upstream communications signal. The upstream communications data 2020a-n and
the no-data indicator 2023 are then combined by splitter/multiplexer 2025. The
upstream communications data 2020a-n and the no-data indicator 2023 are
transmitted in their respective timeslots 2030a-n of upstream communications
frame
2035.
The OLT 2005, via the upstream communications path 2015, receives the 10
upstream commuriications frame 2035. The OLT 2005 then demultiplexes (or
separates) the upstream communications frame 2035 into individual timeslots
2030a-n. Consequently, the OLT 2005 receives from each conununicating ONT
2010a-n upstream communications data 2020a-n. The OLT 2005 also receives the
no-data indicator 2023 from the non-communicating ONT 2013.
While the OLT 2005 is "receiving" the no-data indicator 2023 in the timeslot
2030c of the upstream communications frame 2035, a no-input signal power level
on
the upstream communications path 2015 may be measured. In another example
embodiment, a no-input signal power level may be measured on an upstream
communications path at a time there are no upstream communications for least a
portion of at least one timeslot in an upstream communications frame.
In contrast to the previous example, the non-communicating ONT 2013 may
send an "idle" signal (not shown) or a message indicating there is no data to
be sent
(not shown). In this situation a no-input signal power level on the upstream
communications path 2015 cannot be measured.
FIG. 21A is an example embodiment of the invention in which an upstream
communications frame 2105 has n number of timesiots 2110a-n. Each timeslot
2110a-n grants (or allocates) a time for upstream communications 2115
(referred to
herein as ts,ot). It is during the tsiot 2115 that upstream communications
data is
communicated from an ONT to an OLT. In the upstream communications frame
2105, an "unused" timeslot (i.e., a timeslot without upstream communications
data)
defines a time for no-upstream communications 2120 (referred to herein as t ).
It
quiet
is during the tquiet 2120 that a no-input signal power level on an upstream
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communications path may'be measured. An unused timeslot such as t 2120 may
quiet
occur in networks with more timeslots than ONTs.
In this example embodiment, the tqU1e1 2120 is equal to the tSiot 2115. As
such,
if the tsio, is 1.2 s, for example, the no-input signal power level on an
upstream
communications path may be measured for as long as 1.2 s.
FIG. 21B is another example embodiment illustrating a time for no-upstream
communications 2120 (referred to herein as tqu1e1) optionally equal to some
whole
multiple of a time for upstream communications 2115 (referred to herein as
tsiod.
For example, if the tsiot 2115 is 1.2 s, the t quict 2120 may be two, three,
etc., times
*10 the length of the tsiot 2115. Accordingly, a no-input signal power level
on an
upstream communications path.is measured for 2.4 s, 3.6 s, etc., where the
longer
time typically results in improved accuracy of the power level measurement.
FIG. 21 C is yet another example embodiment in which a time for no-
upstream communications 2120 (referred to herein as tquit1) is equal to some
fraction
of a time for upstream communications 2115 (referred to herein as tslod. For
example, if the tslot 2115 is 1.2 s, the tqu1C12120 may be a quarter, one and
half, etc.
times the length of the tsiot 2115. Accordingly, a no-input signal power level
on an
upstream communications path may be measured for 0.3gs, 1.8 s, etc.
In still yet other example embodiment, a no-input signal power level on an
-upstrearn communications path may be measured during a time there are no
upstream communications (e.g. , tqu1e1 2120 or when no communications frames
are
communicated in an upstream direction) and then averaged, resulting in an
averaged
measurement, to increase noise immunity. By measuring a no-input signal power
level on an upstream communications path at a time there are no upstream
conununications, an error condition of very small optical power levels can be
detected. Having detected such an error condition, a determination may be made
as
to whether the error condition may lead to layer 2 communications errors, such
as
errors in the ranging or normalization parameters.
FIG. 22 illustrates a ratio between a one-bit input signal power level 2205
and a zero-bit input signal power level 2210. This ratio is ieferred to herein
as an
extinction ratio 2215. The extinction ratio 2215 is a measure of a contrast
(or a
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distinction) between power levels of input signals designating a one-bit input
signal
and a zero-bit input- signal. For example, if the extinction ratio 221-5 is
large, the
distinction between a one-bit input signal power level and a zero-bit input
signal
powei level is also large.
Because the distinction between the power levels is large, an optical receiver
has an easier task in detecting an input signal as either a one-bit input
signal or a
zero-bit input signal. In contrast, if the extinction ratio 2215 is small, the
distinction
between a one-bit input signal power level and a zero-bit input signal power
level is
also small, and an optical receiver has a more difficult task in detecting an
input
signal as either a one-bit input signal or a zero-bit input signal.
A similar ratio may be said to exist between the zero-bit input signal power
level 2210 and a no-input signal power level 2220. This ratio is. referred to
herein as
a no-input extinction ratio 2225. Like the extinction ratio 2215, the no-input
extinction ratio 2225 is a measure of a contrast (or a distinction) between a
power
level of an input signal designating a zero-bit input signal and a power level
of a no-
input signal. For example, if the no-input extinction ratio 2225 is large, the
distinction between a zero-bit input signal power level and a no-input signal
power
level is also large. Because the distinction between power levels is large, an
optical
receiver has an easier task in detecting a zero-bit input signal or a no-input
signal. In
contrast, if the no-input extinction ratio 2225 is small, the distinction a
zero-bit input
signal power level and a no-input signal power level is also small, and an
optical
receiver has a more difficult task in detecting a zero-bit input signal or a
no-input
signal.
Difficulties in distinguishing between a no-input signal and a zero-bit input
signal may also lead to difficulties in distinguishing between a one-bit input
signal
and a zero-bit input signal. As a consequence, there may be an increase in the
number of bit errors which occur during normal communications. As such, it
desirable to have a no-input extinction ratio which is sufficiently large
enough to
prevent such bit errors.
FIG. 23A is a power level diagram illustrating a no-input signal 2305 which
has a power level at time tinitiai 2310 equal to a power level at time t fnal
2315. The
power level of the no-input signal 2305 (i.e., no-input signal power level)
may be
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integrated (or added) by an integrator 2320 (or other electronics) in an
optical power
receiver (or transceiver) to produce an integrated no-input signal power level
2325.
The integrator 2320 integrates from time t~~~~ia, to time tf~nai, resulting in
an integrated
no-input signal power level at tfinal 2330 being greater than an integrated no-
input
signal power level at tinitial 2335, as is expected. The longer the period of
integration
time, the higher the integrated no-input signal power level 2325 is ramped (or
increased). Consequently, over time, a no-input extinction ratio (see FIG. 22)
becomes smaller, and it is more difficult to distinguish a no-input signal
from a zero-
bit input signal. Further, the higher the integrated no-input signal power
level at
tinitial 2335, the more significant the resulting integrated no-input signal
power level
2325 becomes over time and the smaller a no-input extinction ratio becomes
over
the same time." .
FIG. 23B is a diagram illustrating how a transmitted optical power level
from a faulty ONT affects measurement during ranging of an ONT by an OLT. A
message diagram 2300a illustrates an exchange of ranging messages between an
OLT 2301 and an ONT 2302 during a ranging window 2355. A transmitted power
level versus time plot 2300b illustrates the ONT 2302 transmitting a no-input
signal
power level 2303 during the ranging window 2355. A received power level versus
time plot 2300c illustrates the OLT 2301 receiving the no-input signal power
level
2303, which has been integiated by an integrator 2304 in a receiver (not
shown) of
the OLT 2301, as an integrated no-input signal power level 2345.
The transmitted power level versus time plot 2300b indicates that the no-
input signal power level 2303 may be constant during the ranging window 2355,.
where the constant level may be a normal low level (e.g., -40dBrn) or a faulty
high
.25 level (e.g., between -30dBm and -25dBm, or higher). The integrated no-
input signal
power level 2345- ramps up from an integrated no-input signal power level at
time
tinitial 2340 to an integrated no-input signal power level at time tfnal 2350
over the
ranging window 2355.
In operation, while the no-input signal power level 2303 is being integrated
over the ranging window 2355, the OLT 2301 sends a ianging request 2360 to the
ONT 2302. The ONT 2302, in turn, responds with a ranging response 2365. The
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OLT 2301, having sent the ranging request 2360, receives the ranging response
2365
from the ONT 2302 during the ranging window 2355 or it reports. a ranging
error.
Typically, the receiver of the OLT 2301 is reset between adjacent upstream
timeslots to accommodate power levels which vary from ONT to ONT. During
ONT ranging, however, an upstream timeslot is effectively enlarged to
accommodate variability in supported fiber lengths, i.e., more than one
timeslot is
used for the ranging window 2355. For example, the ONT 2302 may be located up
to 20 kilometers away from the OLT 2301. To accommodate this distance, the
duration of the ranging window 2355 is set sufficiently long enough to allow
the
ONT 2302 located 20 kilometers away from the OLT 2301 to receive the ranging
request 2360 and the OLT 2301 to receive the ranging response 2365.
When the duration of the ranging window 2355 is set for a long period of
time, the receiver of the OLT 2301 is not reset during this period of time. As
a
result, no-input signal power levels from non-transmitting ONTs on the ODN
have
more time to be integrated by the receiver of the OLT 2301, thus increasing
the
integrated no-input signal power level 2345. This increase has a negative
impact on
a signal condition circuitry in the receiver of the OLT 2301. In other words,
the
longer the duration of the ranging window 2355, the greater the effects of a
small
no-input extinction ratio (see FIG. 22). Consequently, it may be difficult to
distinguish between a zero-bit input signal power level and a one-bit input
signal
power level possibly leading to upstream communications problem(s).
In one embodiment of the present invention, prior to ranging an ONT, an
OLT instructs communicating ONTs to halt upstream communications. Despite
upstream communications being halted, there still may be a no-input signal
from one
or more halted ONTs causing a "faulty no-input signal power level" (see FIG.
19).
Consequently, the faulty no-input signal power level may be integrated,
causing the
integrated no-input signal power level 2345 to increase further.
FIG. 24A is a block diagram of an example OLT 2405 in communication
with an ONT 2410. In this particular example, the OLT 2405 has a PON card
2415.
The PON card 2415 includes a processor 2420 communicatively coupled to a
receiver 2425 and a transmitter 2430. Altematively, the receiver 2425 and the
transmitter 2430 may be integrated into a single transceiver (not shown). In
the
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direction toward from the OLT 2405, the receiver 2425 (or transceiver)
receives
upstream communications 2435. The processor 2420 subsequently processes the
upstream communications 2435. In the opposite direction toward the ONT 2410,
the processor 2420 sends, via the transmitter 2430 (or transceiver),
downstream
communications 2440.
FIG. 24B is a block diagram which illustrates an example processor 2445,
supporting example embodiments of the invention, operating in a PON card of an
OLT. The processor 2445 may include a measurement unit 2450, a comparison unit
2455, and a notification generator 2460. Alternatively, some or all of the
aforementioned components may not be co-located with the processor 2445, but
may be remotely located connected via a communications bus (not shown).
In operation of this example embodiment, the measurement unit 2450 may
measure a power level of a no-input signal 2401 on an upstream communications
path. The measurement unit 2450 may include an integrator, such as the
integrator
2320 of FIG: 23A, or other electronics to measure the power level of the no-
input
signal 2401. A measured no-input signal power level 2402 may be compared
against a threshold value 2403 by the comparison unit 2455. A result 2404 from
the
comparison unit 2455. is communicated to the notification generator 2460. The
notification generator 2460 may generate a notification if the communicated
result
2404 indicates the measured no-input signal power level 2402 exceeds the
threshold
2403. Keeping the integrated no-input signal power levels of FIGS. 23A and 23B
in
mind, it should-be understood that the comparison unit 2455 may compare a
maximum, an average (at multiple times or over a length of time), or a portion
of the
measured no-input signal power level 2402 against the threshold 2403.
The threshold 2403 against which the measured no-input signal power level
2402 is compared may be determined or defined in multiple ways. For example,
the
threshold 2403 may be set to a value equal to a "tolerable no-input signal
power
level" multiplied by a number of ONTs in communication with the OLT. Field
experience may indicate a no-input signal power level of -20dBm to -30dBm per
ONT often leads to problems in upstream communications. Based on such
experience, the tolerable no-input signal power level may be -40dBm.
Therefore, in
an example network having thirty-two ONTs communicating with an OLT, the
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threshold may be calculated as -40dBm multiplied by thirty-two. Additionally,
losses between the ONTs and the OLT (i.e., ODN losses) may be accounted for in
calculating the threshold. In another example embodiment, the tolerable no-
input
signal power level may be less than a zero-bit input signal power level
specified for
the ONTs. One skilled in the art will readily appreciate that the value of the
tolerable no-input signal power level may not be fixed (i.e., set to the same
level for
all communications networks, but rather may depend on characteristics of a
communications network.
The threshold 2403.may altematively represent a maximum power level
corresponding to a fault associated with upstream communications in a non-
communicating state. In another example embodiment, the threshold 2403 may be
less than a sum of a zero-bit input signal power level of each ONT offset by
respective losses between the ONTs and the OLT. It should be understood that
the
threshold 2403 may be predetermined based on a configuration of a passive
optical
network or determined based on some other metric.
Continuing to refer to FIG. 24B, the notification generator 2460 may
generate a remote notification 2465 which is sent over a network 2466 to, for
example, a remote user or remote management system 2467. Alternatively, the
notification generator 2460 may generate a local notification 2470, which is
presented locally to, for example, a local user or local management system
2471. It
should be understood that the remote notification 2465 may be any form of
signal
(e.g., analog, digital, packet, and so forth), data values, including in
header or load
portions of packets, and so forth. The local notification 2470 may also be any
form
of signal or may be audio or visual alarms to alert an operator at a console
at the
OLT that an error as described herein had occurred.
FIG. 25A is a flow diagrarri illustrating an example process 2500 for
diagnosing a problem on an ODN. A no-input signal power level on an upstream
communications path may be measured (2505) at a time no upstream
communications are on the upstream communications path. The measured no-input
signal power level may be compared (2510) against a threshold. If the measured
no-
input signal power level on the upstream communications path is greater than
the
threshold, a notification may be issued (2515) to alert an operator (or
management
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system) that the threshold is exceeded. If, however, the measured no-input
signal
power level on the upstream communications path is not greater than the
threshold,
the process 2500 may return to begin measuring (2505) the no-input signal
power
level.
FIG. 25B is a flow diagram illustrating a process 2520 for diagnosing a
problem on an ODN in accordance with an example embodiment of the invention.
A no-input signal power level on an upstream communications path may be
measured (2525) at a time no upstream communications are on the upstream
communications path. In this example embodiment, the no-input signal power
level
is measured during a time for no upstream communications (tquict ). In
reference to
F1GS. 21A-21C, the time for no upstream communications (tqu <) may be equal to
a
time for upstream communications (tsiol). Alternatively, the time for no
upstream
communications (tquiet ) may be equal to.a whole multiple or fraction of the
time for
upstream communications (tsiod.
Next, a threshold may be calculated (2530). In this example embodiment,
the threshold is equal to a number of ONTs on the ODN multiplied by a
tolerable
no-input signal power level. The tolerable no-input signal power level may be
estimated based on system modeling, equal to a value measured at a time known
not
be experiencing an error condition (e.g., initial system set-up), and so
forth.
The measured no-input signal power level on the upstream communications path
may be compared (2535) against the calculated threshold. If the measured no-
input
signal power level is greater than the calculated threshold, a notification
may be
issued (2540) that the calculated threshold is exceeded. If however, the
measured
no-input signal power level on the upstream communications - path is less than
the
calculated threshold, the process 2520 may wait (2545) for the time for no
upstream
communications (tqU1et) to reoccur. After waiting, the process 2520 may once
again
measure (2525) the no-input signal power level on the upstream communications
path.
The above description referring to FIGS. 18-25B describes diagnosing
problems on a time division multiple access (TDMA) optical distribution
network
(ODN), such as a passive optical network (PON). An example method may include:
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(i) measuring no-input signal power level on a communications path configured
to
carry upstream communications between multiple optical network terminals
(ONTs)
and an optical line terminal (OLT) in a passive optical network (PON) at a
time no
upstream communications are on the communications path from the ONTs to the
OLT; (ii) comparing the measured no-input signal power level to a threshold;
and
(iii) generating a notification in an event the threshold is exceeded. Through
the use
of this method, faults in optical transmitters, such as bad solder joints, can
be
determined. Such faults may cause errors in parameters, such as ranging or
normalization parameters, associated with communications. By determining the
faults, the time required to resolve communications errors can be reduced.
FIGS. 26-42 illustrate example embodiments of an aspect of the present
invention in which a transport layer ranging window has a longer duration than
a
physical layer ranging window. The transport layer ranging window defines a
range
within which an optical network terminal (ONT) can respond to a ranging
request
without affecting upstream communications from other ONTs on a passive optical
network (PON), and the physical layer ranging response defines a time within
which
a receiver in a optical line terminal (OLT) is enabled to receive a ranging
response
from the ONT. By keeping the transport layer ranging window sufficiently long
in
duration, ranging responses from ONTs at unspecified ranges can be captured.
By
shortening the physical layer ranging window, errors due to noise or faulty
ONT
output power can be reduced.
As previously described, diagnosing a passive optical network (PON) for
problems may involve detecting, prior to establishing layer 2 communications,
a
malfunctioning optical network terminal (ONT). A malfunctioning ONT may be
detected by looking for an inappropriate presence of a modulated or
unmodulated
upstream optical signal when no signal should be present on the upstream
communications path. The inappropriate presence of such signals may cause a
power level associated with these.signals (i.e., a no-input signal power
level) to be'
integrated over time by an integrator in a receiver to produce an integrated
no-input
signal power level. As expected, over time the integrated no-input signal
power
level increases, causing a no-input extinction ratio to become smaller.
Consequently, it becomes more difficult to distinguish a no-input signal from
a zero-
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bit input signal, possibly leading to bit errors. In less severe cases, a
higher than
expected no-input signal power level may result in erroneous settings of
parameters
used in connection with upstream communications.
The effect of integrating a no-input signal power level is particularly
significant when ranging an ONT. While ranging, an integrator (or other
electronics) in an optical line terminal (OLT) receiver (or transceiver) may
integrate
(or otherwise calculate) a no-input signal power level for an extended period
of time.
Accordingly, what is needed is a method or a corresponding apparatus for
ranging
an ONT in a passive optical network in a manner minimizing the aforementioned
effects caused by the inappropriate presence of an unmodulated or modulated
optical
signal ori the upstream communications path or other times when such presence
causes adverse effects, directly or indirectly on upstream communications. It
should
be understood that alternative embodiments may be employed in situations
involving downstream communications.
Intemational Telecommunication Union (ITU) specification 983.1, Section
8.4.2.5.2, describes shortening a ranging window when the location of an ONT
to be
ranged is known. With a priori knowledge, a ranging window may be shortened to
correspond to a known distance between the OLT and the ONT. According to
shortening the ranging window done in prior art systems by reducing a
transport
layer ranging window (layer 2) and a physical layer ranging window (layer 1)
in
equal amounts.
By shortening a ranging window, disruption to communicating ONTs is
minimized. Since communicating ONTs are disabled from communicating in the
upstream direction during ranging, the shorter the ranging window, the shorter
the
amount of-time upstream communications must be halted. Consequently, the
negative impact of ranging on the throughput of communicating ONTs is lessen
by
using a shortened ranging window.
In contrast, when the location of the ONT is unknown, it possible the ONT is
located at a possible maximum distance (e.g., 20 Km)'away from the OLT. As
such,
to accommodate this maximum distance, a maximal ranging window must used.
FIG. 26 is a message diagram illustrating an OLT 2605 ranging an ONT 2610. To
range the ONT 2610, the OLT 2605 transmits a ranging request 2615. The ONT
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2610, in response to the transmitted ranging request 2615, transmits a ranging
response 2620. The OLT 2605, having received the ranging response 2620,
determines a metric associated with the ranging response 2620 for use in
connection
with upstream communications between the OLT 2605 and the ONT 2610. For
example, a round-trip time 2625 may be determined, where the determined round-
trip time 2625 represents a time from when the OLT 2605 transmits the ranging
request 2615 to the time the OLT 2605 receives the ranging response 2620. It
should be understood that ranging cycles may be calculated other ways, such as
a
one-way trip time of a ranging request 2615 or a ranging response 2620.
In one embodiment, the OLT 2605 sets at least one parameter, used in
connection with upstream communications between the OLT 2605 and the ONT
2610, based on at least one metric associated with the ranging response 2620.
For
example, the OLT 2605, based on the round-trip time 2625, may set an
equalization
delay 2630. The OLT 2605 may then send the ONT 2610 the equalization delay
2630 or command the ONT 2610 to set an intemal parameter based on the
equalization delay 2630. In an example embodiment, the equalization delay 2630
is
conveyed via a message 2635. During later communications with the OLT 2605 in
this example embodiment, the ONT 2610, in turn, waits for a time according to
the
equalization delay 2630 before sending upstream communications data 2640. In
one
embodiment, the ONT 2610 uses the equalization delay 2630 to have the upstream
communications data 2640 reach in the OLT 2605 during a predefined timeslot
relative to upstream communications data from other ONTs (not shown), as known
in the art.
Previously described in reference to FIGS. 20B and 23B, a ranging window
is further described in FIGS. 27A and 27B.
FIG. 27A illustrates, in connection with a transport layer ranging window
2705, an OLT 2715 transmitting a ranging request 2720 and an ONT 2725, among a
group of ONTs 2710a-n, transmitting a ranging response 2730. During the
transport
layer ranging window 2705, upstream communications from communicating ONTs
2710a-n are halted (or set in a"quiet" state).
In FIG. 27A, the transport layer ranging window 2705 starts with the OLT
2715 transmitting a last-bit 2735 of the ranging request 2720. Presented
differently,
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the ranging request 2720 is transmitted before the transport layer ranging
window
2705 begins. Alternatively, referring to FIG. 27B, a transport layer ranging
window
2755 starts with an OLT 2765 transmitting a first-bit 2785 of a ranging
request
2770, so the ranging request 2770 and ranging response 2780, are transmitted
during
the transport layer ranging window 2755. As such, the duration of the
transport
layer ranging window 2705 of FIG. 27A may be shorter than the duration of the
transport layer ranging window 2755 of FIG. 27B. Consequently, upstream
communications from ONTs 2710a-n of FIG. 27A may be halted for a shorter
period
of time than upstream communications from ONTs 2760a-n of FIG. 27B. In other
embodiments, the transport layer ranging window 2705 and 2755 of FIGS. 27A and
27B, respectively, are the same duration or the transport layer ranging window
2755
of FIG. 27B is shorter than the one of FIG. 27A.
For the remainder of this disclosure, a ranging request is described as being
transmitted during a transport layer ranging window unless otherwise
specified. It is
noted, however, that example embodiments of the invention are not limited to a
transport layer ranging window starting with a first bit of a ranging request
being
transmitted. Example embodiments of the invention are also applicable to a
transport layer ranging window starting with transmission of a last-bit of a
ranging
request.
As described previously in reference to FIG. 23B, an integrated no-input
signal power level may ramp (or increase with time) over a transport layer
ranging
window. Due to the duration of the transport layer rariging window and ramping
the.
integrated no-input signal power level over this duration,.a no-input
extinctiori ratio
(see FIG. 22) may be small. In such a case, it may be difficult to distinguish
a no-
input signal from a zero-bit input signal, possibly leading to upstream
communications problems. To minimize this potential source of communication
errors, example embodiments of the invention monitor for a ranging response
during
a portion of the transport layer ranging window rather than during the entire
transport layer ranging window.
FIG. 28 illustrates a transport layer ranging window 2805 having, for
example, a duration of 100 s (microseconds). A physical layer ranging window
2810 within the transport layer ranging window 2805 may have a duration that
is
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based, in part, on a duration of an expected ranging response 2815. For
example, the
duration of the physical layer ranging window 2810 may be twice the duration
of the
ranging response 2815. As such, the duration of the physical layer ranging
window
2810 is 10 s if the duration of the ranging response 2815 is 5 s. In another
example, the duration of the physical layer ranging window 2810 may be some
multiple of the duration of the ranging response 2815 plus some time for a
delimiter
or other overhead (not shown) associated with transmitting the ranging
response
2815.
FIG. 29A illustrates a transmitted power level versus time plot 2900a in
which, during a transport layer ranging window 2901, an ONT (not shown)
transmits a no-input signal power level 2905. A received power level versus
time
plot 2900b further illustrates, during the transport layer ranging window
2901, an
OLT (not shown) receiving the transmitted no-input signal power level 2905.
The transmitted power level versus time plot 2900a indicates the transmitted
no-input signal power level 2905 may be constant during the transport layer
ranging
window 2901. The constant level may be a normal no-input level (e.g., less
than -
40dBm) or a faulty low-level (e.g., between -30dBm and -25dBm, or higher).
The received power level versus time plot 2900b illustrates the duration of
the transport layer ranging window 2901 as being from ti"itiai to tfinal, and
the duration
of a physical layer ranging window 2902 as being from t, to t2. The duration
of the
transport layer ranging window 2901 is greater than the duration of the
physical
layer ranging window 2902, i.e., the time from tiõitial to tf,ai is greater
than the time
from tI to t2.
In general, the effect of any noise on the receiver increases the longer the
physical layer ranging window 2902 is open and decreases the shorter the
physical
layer ranging window is opened. For purposes of illustrating the effects of
noise in a
hardware sense, examples in terrris of an integrator integrating noise are
presented
herein, including immediately below. However, the example is not intended to
be
restrictive in any way.
During the physical layer ranging window 2902 (i.e., from ti to t-,),
monitoring for ranging response may be enabled. While the monitoring is
enabled, a
ranging response received during the physical layer ranging window 2902 may be
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processed. Additionally, while the monitoring is enabled, the transmitted no-
input
signal power level 2905 is received and integrated by an integrator 2906a (or
other
electronics) in a receiver (or transceiver) of the OLT. Consequently, a power
level
measured from T, to T2 increases over time (or ramps) due to integration. This
power level, which may be measured while monitoring is enabled, is referred to
herein as an integrated power level associated with monitoring for a ranging
response (e.g., 2920 and 2935).
In contrast, during a first disabled period 2910a (i_e_, from t;niL1ei to ti)
or
2910b (i. e., from t2 to tf,,,j), monitoring for a ranging response may be
disabled.
While the monitoring is disabled, a ranging response received may not be
processed.
Additionally, while monitoring is disabled, the transmitted no-input signal
power
level 2905 is received, but may not be integrated by the integrator 2906a.
Consequently, power levels measured from tiõit;ai to ti and from b to tf,ai
remain
substantially unchanged (e.g.; 2917a and 2917b). .
At tinitial, the transmitted no-input signal power level 2905 is received by
the
OLT at an initial-power level 2915, which is about the no-input power level
output
by the ONT, less transmission or other losses. Also at tiõitial, the
integrator 2906a is
reset by a reset command 2907a or other mechanism. During the first disabled
period 2910a, the transmitted no-input signal power level 2905 received by OLT
is
not integrated. As such, the transmitted no-input signal power level 2905
received
by the OLT between tiõitial and ti remains non-integrated from the initial-
power level
2915.
At ti, the transmitted no-input signal power level 2905 is received by the
OLT at a first-power level 2925. Since the transmitted no-input signal power
level
2905 is not integrated during the first disabled period 2910a, the initial-
power level
2915 and the first-power level 2925 are substantially equal. During the
physical
layer ranging window 2902, however, the transmitted no-input signal power
level
2905 received by OLT is integrated. As such, an integrated power level
associated
with monitoring for a ranging response 2920 ramps from the first-power level
2925
at t, to a second-power level 2930 at t2.
At t2, the transmitted no-input signal power level 2905 received by the OLT
at the second-power level 2930. During the second disabled period 291 0b, the
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transmitted no-input signal power level 2905 received by the OLT is not
integrated.
As such, the transmitted no-input signal power level 2905 received by the OLT
from
t-2 to tf,,,ai remains substantially unchanged from the second-power level
2930.
In comparison, if monitoring during the transport layer ranging window 2901
(i.e., from t;,,ital to tf,nd) is enabled, an integrated power level
associated with
monitoring for a ranging response 2935 (represented by a dashed line) ramps
from
the initial-power level 2915 at ti~itifli to a final-power level 2940 at
tfõai. Since the
duration of the transport layer ranging window 2901 is longer than the
duration of
the physical layer ranging window 2902, there is more time for the integrated
power
level to increase. Consequently, the measured second-power level 2930, at the
end
of the physical layer ranging window 2902, is less than the final-power level
2940
that would have been measured at the end of the transport layer ranging window
2901 if the physical layer ranging window 2902 was the same length as the
transport
layer ranging window 2901. Accordingly, the above described consequences of
having a small no-input extinction ratio may be minimized by enabling
monitoring
for a ranging response during a physical layer ranging window rather than
during an
entire transport layer ranging window.
Altematively, in FIG. 29B, in a received power level versus time plot 2900c,
during a first disabled period 2960a (from t;,,;,;ai to ti) or 2960b (from t2
to trõai),
monitoring for ranging response may be disabled in a different manner as
compared
to FIG. 29A. In the embodiment of FIG. 29B, while the monitoring is disabled,
a
ranging response received may not be processed (e.g., by hardware, firmware,
or
software), but the transmitted no-input signal power level 2905 may be
integrated by
an integrator 2906b. Consequently, power levels measured from tiõit;al to ti
and from
t---) to trõai increase over time (or ramp). These power levels, which may be
measured
while monitoring is disabled, are referred to herein as integrated power
levels (e.g.,
2963 and 2978), in comparison to the integrated power level associated with
monitoring for a ranging response (2920 and 2935) for FIG. 29A.
At tiõitiai, the transmitted no-input signal power level 2905 is received by
an
OLT at an initial-power level 2965, which is about the no-input power level
output
by an ONT, less transmission or other losses. During the first disabled period
2960a, the transmitted- no-input signal power level 2905 received by the OLT
is
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integrated. As such, beginning at tin;,;ai, an integrated power level 2963
ramps from
the initial-power level 2965 to a first-power level 2970 at t).
At Ti, the integrator 2906b is reset by a reset command 2907b. Resetting the
integrator 2906b resets the integrated power level 2963 from the first-power
level
2970 to a reset power leve12975. During the physical layer ranging window
2902,
the transmitted no-input signal power level 2905 received by the OLT is
integrated.
As such, beginning at ti, an integrated power level 2973 associated with
monitoring
for a ranging response ramps from the reset power level 2975 to a second-power
level 2980 at t2.
At t2, the transmitted no-input signal power level 2905 is received by the
OLT at the second-power level 2980. During the= second disabled period 2960b,
the
transmitted no-input signal power level 2905 received by the OLT is
integrated. As
such, beginning at t2, an integrated power level 2978 ramps from the second-
power
level 2980 to a final-power level 2985 at tfr,ai.
An ONT may be located up to some distance away from an OLT, for
example 20 Km. To accommodate such distarice, the duration of a transport
layer
ranging window is set suf-ticiently long enough to allow the ONT to receive a
ranging request, within which an ONT can respond to a ranging request without
affecting upstream communications from other ONTs on the ODN, and the OLT to
receive a ranging response. As such, the ranging request may be located in
time
anywhere within the transport layer ranging window. Consequently, the issue is
what portion of the transport layer ranging window to monitor for (or to
otherwise
locate), in time, a ranging response. One approach may be to repeatedly
transmit a
ranging request and monitor for a ranging response, where physical layer
ranging
window(s) is/are located in the transport layer ranging window at different
location(s) each cycle until the location, in time, of the ranging response is
f6und
within the transport layer ranging window.
FIG. 30 is a series of timing diagrams illustrating dynamically adjusting a
physical layer ranging window in an iterative manner within a transport layer
ranging window 3001 to locate a ranging response 3010a-c. By way of example,
FIG. 30 illustrates a binary search. One skilled in the art will ieadily
recognize other
types of searches are equally applicable, for example, a search based on a
hash
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algorithm. Furthermore, one skilled in the art will readily recognize a
transport layer
.ranging may be approximated through dynamic adjustment of the duration,
delay,
number, or combination thereof, of a physical layer ranging window. Hardware,
firmware, or software may be employed to support or execute the search as
understood in the art.
The transport layer ranging vAndow 3001 may be approximated by a first-half
physical layer ranging window 3015 and a second-half physical layer ranging
window 3016. In a first iteration 3003a, a ranging request 3005a is
transmitted, but
a ranging response 3010a is not received during the first-half physical layer
ranging
window 3015. In a second iteration 3003b, a ranging request 3005b is
transmitted,
and a ranging response 3010b is received during the second-half physical layer
ranging window 3016. Accordingly, the ranging response 3010b is located, in
time,
during a second-half of the transport layer ranging window 3002.
To locate a ranging response in time with more accuracy, the second-half of
the transport layer ranging- window 3002 may be approximated by a first-
quarter
physical layer ranging window 3020 and a second-quarter physical layer ranging
window (not shown). In a third iteration 3003c, a ranging request 3005c is
transmitted, and a ranging response 3010c is received during the first-quarter
physical layer ranging window 3020. Accordingly, the ranging response 3010c is
located, in time, during a first-quarter of the second-half of the transport
layer
ranging window 3002. Presently differently, the ranging response 3010c is
located,
in time, during a third-quarter of the transport layer ranging window 3001.
It should be understood that the example illustrated in FIG. 30 is a
simplified
example. In practice, hundreds or thousands of attempts to locate a ranging
response
3010a-c may be performed.
One skilled in the art wiIl readily recognize the transport layer ranging
window 3001 may be even further divided to locate a ranging response, in time,
with
more accuracy. The number of times a transport layer ranging window is divided
in
order to locate a ranging response, in time, may depend on the duration of the
ranging response. For example, to locate a ranging response of 5 gs, a
transport
layer ranging window of 100 s may be divided up to sixteen times to locate
the
ranging response, in time. In addition to dynamically adjusting the physical
layer
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ranging window within the transport layer ranging window, a transport layer
ranging
window may also be approximated by shifting one or more physical layer ranging
windows.
FIG. 31 is a series of timing diagrams illustrating-another example of
searching for a ranging response by dynamically adjusting a position, in time,
of the
physical layer ranging window within a transport layer ranging window. In FIG.
31,
in a first iteration 3103a, during or otherwise in connection with a transport
layer
ranging window 3110a, a ranging request 3115a is transmitted, but a ranging
response 3120a is not received during a physical layer ranging.window 3125a.
In a
second iteration 3103b, during a transport layer ranging window 3110b, a
ranging
request 3115b is transmitted. A physical layer ranging window 3125b is
shifted, in
time, with respect to the first iteration physical layer ranging window 3125a,
but a
ranging response 3120a remains not received during the shifted physical layer
ranging window 3125b. In an nth iteration 3103n, during a transport layer
ranging
window 31 I On, a ranging request 3115n is transmitted. A physical layer
ranging
window 3125n is shifted, in time, with respect to previous physical layer
ranging
windows. In this nth iteration 3103n, a ranging response 3120n is received
during
the shifted physical layer ranging window 3125n.
Having found the ranging response 3120n during the physical layer ranging
window 3125n, transmitting'a ranging request, monitoring for a ranging
response,
a nd shifting a physical layer ranging window may or may not repeat. In one
example embodiment, the transmitting, monitoring, and shifting repeat at least
until
a ranging response is received during a physical layer ranging window. In
another
example embodiment, the transmitting, monitoring, and shifting repeat for a
fixed,
variable or otherwise predetermined number of repetitions. In addition to
shifting a
physical layer ranging window non-incrementally within a transport layer
ranging
window, a physical layer ranging.window may be shifted incrementally across
the
transport layer ranging window.
In both FIGS. 30 and 31, the physical layer ranging window is set slightly
longer in duration than the expected duration of a ranging response to keep a
metric,
calculated by integrating a no-input signal power level, to an acceptable
error level,
where the acceptable error level is one within which parameter(s) based upon
the
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metric and used for upstream communications during normal operations do not
adversely affect the upstream communications.
FIG. 32A is a series of timing diagrams illustrating a search technique in
which a physical layer ranging window is shifted across a transport layer
ranging
window in equal steps. In FIG. 32A, in a first iteration 3201 a, during a
transport
layer ranging window 3203a, a ranging request 3205a is transmitted, but a
ranging
response 3215a is not received during a physical layer ranging window 3210a.
In a
second iteration 3201b, a ranging request 3205b is transmitted, and a physical
layer
ranging window 3210b is shifted, in time, relative to the previous physical
layer
ranging window 3210a, across a transport layer ranging window 3203b by a shift
increment 3211. A ranging response 3215b is not received during the shifted
physical layer ranging window 3210b. In a third iteration 3201 c, a ranging
request
3205c is transmitted, and a physical layer ranging window 3210c is again
shifted, in
time, relative to the previous physical layer ranging window 3210b, across a
transport layer ranging window 3203c by the shift increment 3211. Again, a
ranging
response 3215c is not received during the shifted physical. layer ranging
window
3210c.
In an nth iteration 3201n, a ranging request 3205n is transmitted in a
transport layer ranging window 3203n, and a ranging response 3215n is received
during a physical layer ranging window 3210n shifted, in time, relative to a
previous
(n-1)th physical layer ranging window (not shown) by the shift increment 3211.
In this embodiment, the shift increment 3211 shifts the physical layer
ranging window 3210a-n, in time, by an amount equal to some whole number
multiple of the duration of the physical layer ranging windo.w 3210a-n. For
example, a physical layer ranging window of 10 s may be shifted, in time,
incrementally by 10 s, 20 s, 30 s, etc. across the transport layer ranging
window.
FIG. 32B is a series of timing diagrams which collectively illustrate another
example embodiment of searching for a ranging response within a transport
layer
ranging window. A physical layer ranging window 3240a-n is shifted, in time.
by a
shift increment 3241. The shift increment 3241 is some fraction of the
physical
layer ranging window 3240a-n. For example, a physical layer ranging window of
10
s may be shifted, in time, incrementally by 5 s, 15 s, 25 s, etc. across
the
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transport layer ranging window 3233a-n. From a first iteration through an nth
iteration 3231a-n, a ranging request 3235a-n is transmitted, and a physical
layer
ranging window 3240a-n is shifted by the shifting increment 3241 at least
until a
ranging response 3245a-n is received during a physical layer ranging window,
which
occurs in this example during the nth physical layer ranging window 3240n.
In some cases, the physical layer ranging window. (PLRW) shift techniques
of FIGS. 32A and 32B may not result in successful ranging should a ranging
response being partially aligned with the physical layer ranging window. One
way
of preventing this is to overlap any two adjacent ranging windows by an amount
greater than or equal to the ranging response to ensure that if the tail end-
of the
ranging response is just missed (e.g., by one PLRW), the very beginning of the
ranging response is not missed by the next PLRW.
In general if the PLRW is Y times the duration ranging response (RR) (i.e.,
PLRW = Y x RR), the PLRW can be shifted no more that RR/(Y -1) in order to
guarantee that, if the very last bit of the ranging response is truncated by
the current
position of the PLRW, the next shifted PLRW does not truncate the very first
part of
the ranging response.
For example, in reference to FIG. 32A, if the duration of the PLRW is equal
to two times (2x) the duration of the ranging response, there is a shift of
less than
RR of the PLRW. In the FIG. 32B example, if the duration of the PLRW is equal
to
one and one-half times (1.5x) the duration of the ranging response, there is a
shift,of
less than one-half (0.5) of the RR to a subsequent PLRW.
FIG. 32C is a series of timing diagrams which collectively illustrate another
example embodiment of searching for a ranging response within a transport
layer
ranging window. A physical layer ranging window 3270a-n is shifted, in time,
by a
variable shift increment 3272. The variable shift increment 3272 shifts the
physical
layer ranging window 3270a-n, in time, by some amount. The amount shifted may
be random or pseudo-random. Optionally, the physical layer ranging window
3270a-n may be shifted, in time, by an amount according a geometric series, a
logarithmic series, or other series. As such, from a first iteration through
an nth
iteration 3271 a-n, a ranging request 3255a-n is transmitted, and the physical
layer
ranging window 3270a-n is shifted in transport layer ranging windows 3273a-n
by
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the variable shifting increment 3272 at least until a ranging response 3275a-n
is
received during a physical ranging window, which occurs in this example in the
nth
physical layer ranging window 3270n.
FIG. 33 is a series of timing windows which illustrate an example technique
of adjusting timing of a physical layer ranging window in an event only part
of a
ranging response is received during a physical layer ranging window. In an (n-
I)th
iteration 3301n-1, during a transport layer ranging window 3305a, a ranging
request
3310a is transmitted. During the transport layer ranging window 3305a, a
ranging
response 3315, in part, is received during a physical layer ranging window
3320a.
The portion of the ranging response 3315 received during the physical layer
ranging
window 3320a is referred to herein as a received portion 3325, while a
remaining
portion not received is referred to herein as a non-received portion 3330.
In an nth iteration 3301n, during a later transportlayer ranging window
3305b, a ranging request 3310b is transmitted, and a physical layer ranging
window
3320b is shifted, in time. The physical layer ranging windo.w 3320b is
shifted, in
time, by an amount expected to result in receiving a ranging response 3316 in
full
during the physical layer ranging window 3320b. For example, the physical
layer
ranging window 3320b may be shifted, in time, relative to the (n-l)th physical
layer
ranging window 3320a, by an amount equal to the non-received portion 3330.
Alternatively, the physical layer ranging window 3320b may be shifted, in
time, by
an amount greater than the non-received portion 3330. In addition to shifting,
in
time, the physical layer ranging window, in another embodiment, the duration
of a
physical layer ranging window may be lengthened, after a portion of the
ranging
response is received, by an amount expected to allow the ranging response to
be
received during the physical layer ranging window.
FIG. 34 is a series of timing diagrams which illustrate a search technique for
monitoring for a ranging response by adjusting a length of a.physical layer
ranging
window in a dynamic manner. In a first iteration 3401 a, during a transport
layer
ranging window 3405a, a ranging request 3410a is transmitted. During the
transport
layer ranging window 3405a, a ranging response 3415a is not received during a
physical layer ranging window 3420a. In this embodiment, the duration of the
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physical layei ranging window 3420a is lengthened at least until a ranging
response
is received during the lengthened physical layer ranging window.
In an nth iteration 3401n, during a transport layer ranging window 3405n, a
ranging request 3410n is transmitted, and a physical layer ranging window
3420n is
shown in a lengthened state relative to the length of the physical layer
ranging
window 3420a=of the first iteration 3401 a. During the transport layer ranging
window 3405n, a ranging response 3415n is received during the lengthened
physical
layer ranging window 3420n.
In another embodiment, in addition to lengthening the duration, once the
1.0 timing of the ranging response 3415n is known to be within the transport
layer
ranging window 3405n and the physical layer ianging window 3420n; the physical
layer ranging window 3420n can be shortened to reduce noise or. integration
effects
associated with monitoring for the ranging response 3415n.
FIG. 35 is a series of timing diagrams illustrating use of a series of
physical
layer ranging windows to monitor for a ranging response. In a first iteration
3 501 a,
during a transport layer ranging window 3505a, a ranging request 3510a is
transmitted from an OLT to an ONT. During the transport layer ranging windovv
3505a, a ranging response 3515a from the ONT is not received by the OLT during
a
series of physical layer ranging windows 3520a, which includes multiple
physical
layer ranging windows 3 525a-d.
In-an nth iteration 3501n, during a transport layer ranging window 3505n, a
ranging request 3510n is transmitted, arid a series of physical layer ranging
windows
3520n is shown shifted relative to the series of physical layer ranging
windows
3520a of the first iteration 3501a. During the transport layer ranging window
3505n,
a ranging response 3515n is received during a physical layer ranging window
3525d
in the shifted series of physical layer ranging windows 3520n.
Each series of the physical layer. ranging windows 3520a-n may be defined
by more than one physical layer ranging window 3525a-d. During each window
3525a=d in the series of physical layer ranging windows 3520a-n, monitoring is
enabled (described above in reference to FIGS. 29A and 29B) for an amount of
time
equal to or for a portion of each physical layer rangingwindow 3525a-d. Each
physical layer ranging window 3525a-d of the series of physical layer ranging
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windows 3520a-n may be equally "sized," i.e., similar in duration.
Alternatively,
each physical layer ranging window of the series of physical layer ranging
windows
may be differently "sized," i.e., differing in duration. As such, monitoring
for a
ranging response during the series of physical layer ranging windows may be
enabled for regular or irregular durations within the series 3520a-n.
Additionally, in the series of physical layer ranging windows 3520a-n,
between each physical layer ranging window 3525a-d, there may be gaps 3530a-c.
During each gap 3530a-c, monitoring for a ranging response is disabled
(described
above in reference to FIGS. 29A and 29B). In other words, between adjacent
physical layer ranging windows (e.g., 3525a and 3525b) iri the series of
physical
layer ranging windows 3520a-n, monitoring for ranging response is enabled,
then
disabled, then enabled again, and so on. During each gap 3530a-c; monitoring
may
be reset (for example, an integrator may be "zeroed"), including at the
beginning or
the end of each of the gaps 3530a-c.
Furthermore, each physical layer ranging window may be equally "spaced"
from one another with such a gap. That is, monitoring for a ranging response
may
be disabled for a similar duration between adjacent physical layer ranging
windows.
Altematively, adjacent physical layer ranging windows may be unequally
"spaced"
from one other, thus disabling monitoring for different durations. As such,
monitoring for a ranging response during a series of physical layer ranging
windows
may be disabled for regular or irregular durations within the series.
It should be understood that there may be more than four physical layer
ranging windows 3525a-d in each series 3520a-n. For example, there may be
tens,
hundreds, thousands, or millions of physical layer ranging windows in each
series
3520a-n depending on an expected length -of ranging response, length of
transport
layer ranging windows 3505a-n, and implementation features.
FIG. 36A is a series of timing diagrams illustrating a shift in a series of
physical layer ranging windows to locate a ranging response in full. In an (n-
1)th
iteration 3633n-1, during a tratisport layer ranging window 3605a, a ranging
request
3610a is transmitted. During the transport layer ranging window 3605a, a
ranging
response 3615 is received in part during a series of physical layer ranging
windows
3620a. The part of the ranging response 3615 received is referred to herein as
a
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received portion 3625, while the remaining portion not received is referred to
herein
as a non-received portion 3630. The non-received portion may fall within a gap
between the physical layer ranging windows or it may arrive after.the physical
layer
ranging windows are halted following receipt of the received portion 3625.
In an nth iteration 3633n, during a later transport layer ranging window
3605b, a ranging request 3610b is transmitted, and a series of physical layer
ranging
windows 3620b is shifted, in time, relative to the earlier series=3620a. The
series of
physical layer ranging windows 3620b is shifted, in time, by an amount
expected to
result in receiving a ranging response 3616 in full during a physical layer
ranging
window 3622 in the series of physical layer ranging windows 3620b. For
exampie,
the series of physical layer ranging windows 3620b may be shifted, in time, by
an
amount 3631 equal to an amount of time of the non-received portion.3630.
Altematively, the series of physical layer ranging windows 3620b may be
shifted, in
time, by an amount greater than the non-received portion 3630 but still
allowing the
ranging response 3616 to fall within the physical layer ranging window 3622.
FIG. 36B is a series of timing diagrams further illustrating shifting a series
of
physical layer ranging windows to locate a ranging response in full. In an (n-
1)th
iteration 3673n-1, during a transport layer ranging window 3655a, a ranging
request
3660a is transmitted. During the transport layer ranging window.3655a, a
ranging
response 3665 is received in part during a series of physical layer ranging
windows
3670a. A first received portion 3675 of the ranging response 3665 is received
during a first physical layer ranging window 367.7a, while a remaining portion
is not
ceceived during the first physical layer ranging window 3677a. The remaining
portion is referred to herein as a non-received portion 3680. The non-received
portion 3680 may be received during a gap 3678 (see FIG. 35) and/or during
another
physical layer ranging window 3677b of the series 3670a.
In an nth iteration 3673n, during a later transport layer ranging window
3655b, a ranging request 3660b is transmitted, and a series of physical layer
ranging
windows 3670b is shifted, in time, relative to the (n-1)th iteration series
3670a. The
series of physical layer ranging windows 3670b is shifted, in time, by an
amount
3681 expected to result in receiving a ranging response 3666 in full during
one
physical layer ranging window 3672 of the series of physical layer ranging
windows
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3670b. For example, the series of physical layer ranging windows 3670b may be
shifted, in time, by an amount 3681 equal to an amount of time of the non-
received
portion 3680. Alternatively, the series of physical layer ranging windows
3670b
may be shifted, iii time, by an amount greater than the amount of time of the
non-
received portion 3680 but not more than an amount that allows for receipt
within the
window 3672.
In an alternative embodiment, the series of physical layer ranging windows
3670b may be replaced with a subset or just one physical layer ranging window
once
timing of the ranging response within the transport layer ranging window 3655b
is
approximately known.
An ability to detect a partial response may be related to noise reduction
gained by decreasing a size of the physical layer ranging window. In such a
case, an
optional, generalized, search methodology might be as follows: 1) reduce a
size of
the physical layer ranging window until the presence of a ranging response can
be
identified and located; and 2) further shift and reduce the size of the
physical layer
ranging window until the ranging response can be precisely captured. The
presumes
that the noise sensitivity associated with detecting and locating presence of
a ranging
response in full or in part is less than that for completely processing a
ranging
response.
FIG. 37 is a series of timing diagrams that superimposes effects in an OLT of
integration of no-input signal power while waiting to receive a ranging
response
from an ONT. In a first iteration 3703a, during a transport layer ranging
window
3705a, a ranging request 3710a is transmitted. During the transport layer
ranging
window 3705a, the OLT monitors for a ranging response 3715a during a physical
layer ranging window 3720a. During the physical layer ranging window 3720a,
the
OLT integrates and measures a power level 3725a associated with monitoring for
a
ranging response. The measured power level 3725a associated with monitoring.
for a
ranging response may exceed a threshold 3730 (discussed above in reference to
FIG.
24B) due to a long period of integration.
If the measured power level 3725a exceeds the threshold 3730, the physical
layer ranging window 3720a is reduced in duration in a next iteration. In this
example embodiment, transmitting a ranging request"J710a, monitoring for a
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ranging response 3715a, and reducing the duration of the physical layer
ranging
window 3720a repeats at least until the measured power level 3725a associated
with
monitoring for the ranging response 3715a is below the threshold 3730.
Continuing to refer to FIG. 37, in an nth iteration 3703n, during a transport
layer ranging window 3705n, a ranging request 3710n is transmitted, and a
physical
layer ranging window 3720n is reduced in duration relative to the physical
layer
ranging window 3720a of the first iteration 3703a, and possibly other previous
iterations (not shown). During the transport layer ranging window 3705n, the
OLT
(not shown) monitors for-a ranging response 3715n during the reduced physical
layer ranging window 3720n. The OLT measures a power level on an upstream
communications path associated with monitoring for ranging response 3715n. In
the
nth iteration 3703n, the measured power level 3725n associated with monitoring
for
the ranging response 3715n is below the threshold 3730 due to a reduced
integration
time, based on the length of time of the physical layer ranging window 3720n.
FIG. 38 is a block diagram of an example OLT 3805 in communication with
anONT 3807. A transmitter 3810 transmits a ranging request 3815 to the ONT
3807. A monitor unit 3820 monitors for a ranging response 3825 from the ONT
3807. Associated with the monitoring for the ranging response 3825, a
determination unit 3830 determines at least one metric 3835. The at least one
metric
3835 is used in connection with upstream communications between the ONT 3807
and the OLT 3805. Based on the determined metric 3835, a configuration unit
3840
sets at least one parameter 3845. The set parameter 3845 is used in connection
with
upstream communications between the ONT 3807 and the OLT 3805. The
transmitter 3810 may send the at least one parameter 3845 to the ONT 3807 so
that
the ONT 3807 may further communicate (see FIG. 26):
FIG. 39 is a block diagram illustrating an example monitor unit 3905, which
may be used in supporting example embodiments of the invention. The monitor
unit
3905 may include a receiver 3910, a measurement unit 3920, and a control unit
3940. Alternatively, some or all of the aforementioned components may not be
co-
' located in the monitor unit 3905, but may be remotely located and connected
via a
communications bus'(not shown).
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In operation of this example monitor unit 3905, the receiver 3910 may
monitor for a ranging response 3915. In monitoring for the ranging response
3915,
the measurement unit 3920 may measure a power level 3925 associated with
monitoring for the ranging response 3915. The measurement unit 3920 may
further
compare the measured power level 3925 against a threshold 3930 (discussed in.
detail in reference.to FIG. 24B). If the threshold 3930 is exceeded 3932, a
notification 3935 may be sent to the control unit 3940. In response to the
notification 3935, the control unit 3940 may issue a physical layer ranging
window
control 3945 to the receiver 3910. The receiver 3910 may respond by shifting,
in
time, at least one physical layer ranging window (not shown). Alternatively,
the
receiver 3910 may respond by enlarging or reducing the duration of at least
one
physical layer ranging window.
FIG. 40 is a flow diagram illustrating an example process 4000 for ranging
an ONT in a passive optical network in accordance with an example embodiment
of
the invention. In connection with (i.e., before or duririg) a transport layer
ranging
window, a ranging request is transmitted (4005) from an OLT. The process 4000
monitors (4010) for a ranging response during at least one physical layer
ranging
- window in the transport layer ranging window. The process 4000, from
monitoring
(4010), determines (4015) at least one metric associated with the monitored
ranging
response. The determined metric is used in connection with upstream
communications between the ONT in the OLT.
FIG. 41 is a flow diagram illustrating an example process 4100-for ranging
an ONT in a passive optical network in accordance with an example einbodiment
of
the invention. In connection with (i.e., before or during) a transport layer
ranging
window, a ranging request is transmitted (4105) from an OLT. Monitoring for a
ranging response is enabled (4110) for an amount of time equal to a physical
layer
ranging window, or less than a physical layer ranging window where possible in
some network applications. An integrator (or other circuitry) used to measure
a
power level associated with monitoring for a ranging response is reset (4115)
at the
beginning of a physical layer ranging window-or the start of the monitoring.
If a
ranging response is detected or otherwise received in full (4120) during a
physical
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layer ranging window, at least one metric associated with the ranging response
is
determined (4125).
If the ranging response is not received in full (4120), but is received in
part
(4130), a physical layer ranging window is shifted (4135) by an amount
expected to
receive the ranging response in full during a physical layer ranging window in
a later
transport layer ranging window. The process 4100 returns to transmit (4105) a
ranging request during a next transport layer ranging windovv.
If the ranging response is not received in full (4120) and not received in
part
(4130); a physical layer ranging window is shifted (4140). The physical layer
ranging window may be shifted incrementally (in whole number, fractional, or
variable increments) across a transport layer ranging window. After shifting
(4140)
a physical layer ranging window, if the transport layer ranging window is not
yet
covered (4145) by the physical layer ranging window (i.e., monitoring across
the
transport layer ranging window is not complete and a ranging response has not
yet
been found), the process 4100 returns. The process 4100 returns to transmit
(4105)
a ranging request, to enable (4110) monitoring for a ranging response, and to
reset
(4115) the integrator (or other circuitry) used to measure the power level
associated
with monitoring for the ranging response.
FIG. 42 is a flow diagram illustrating an example process 4200 for ranging
an ONT in a passive optical network in accordance with an example embodiment
of
the invention. In connection with (i.e., before or during) a transport layer
ranging
window, a ranging request is transmitted (4205) from an OLT. Monitoring for a
ranging response is einabled (4210) for an amount of time equal to at least
one
physical layer ranging window. An integrator (or other circuitry) used to
measure a
metric, such as a power level, associated with monitoring for a ranging
response is
reset (4215) at the beginning of a physical layer ranging window or the start
of the
monitoring.
If a ranging response is monitored (4220) or otherwise received during a
physical layer ranging window, a metric, such as power level, associated with
the
monitoring is measured (4225). If the measured metric does not exceed a
threshold
(4230), at least one metric associated with the ranging response is determined
(4235). The ONT is consequently ranged.
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If, however, the measured metric exceeds a threshold (4230), a physical layer
ranging window may be reduced in duration (4240). In this example embodiment,
the process 4200 repeats at least until the metric associated with monitoring
for a
ranging response, measured during the reduced physical layer ranging window,
is
less than the threshold.
If a ranging response is not received (4220) during a physical layer ranging
window, the physical layer ranging window may be enlarged in duration (4245).
The process 4200 repeats at least until a ranging response is received during
the
enlarged physical layer ranging window.
The systems of FIGS. 38 and 39 and flow diagrams of FIGS. 40-42 may be
implemented in the form of software, firmware, or hardware. If implemented in
software, the software may be any applicable software language that can be
stored
on a computer readable medium, such as RAM or ROM, or distributed via a
computer network. A general purpose or application specific processor may load
and execute the software, causing the processor to be configured to operate in
a
manner as disclosed herein.
The above description referring to F1GS. 26-42 describes ranging an optical
network terminal (ONT) in a passive optical- network (PON). An example method
may include: (i) transmitting a ranging request from an optical line terminal
(OLT)
to an ONT in connection with a transport layer ranging window; (ii) monitoring
for
a ranging response from the ONT during at least one physical layer ranging
window
within the transport layer ranging window, the transport layer ranging window
having a duration longer than the physical layer ranging window; and (iii)
determining at least one metric associated with the ranging response for use
in
connection with upstream communications between the ONT and the OLT. The
metric(s), used in connection with upstream communications, are accurately
-determined, and communications faults during norrrial operations are thus
reduced.
F1GS. 43-51 illustrate example embodiments of an aspect of the present
invention in which an optical receiver of an optical line terminal (OLT) is
reset at
about a time a ranging signal from an optical network terminal (ONT) is
expected to
be received to minimize the effects caused by an inappropriate presence of an
unrnodulated or modulated optical signal on an upstream communications path.
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During standard ranging, a receiver of an OLT is reset at a time which
corresponds to a closest distance the ONT can be from the OLT (e.g., a time
corresponding to a real distance of 1 kilometer (km) or an "ideal" distance of
0km).
In contrast, when using a rogue tolerant ranging method according to an
embodiment of the present invention, resetting of the receiver of the OLT is
delayed
by a time delay, such as an equalization delay (Te) stored for each ONT. In
this
way, resetting of the receiver is delayed (e.g., by delaying when a reset
signal is
sent) until just before a ranging response from the ONT is expected to be
received.
In other words, a time to reset a receiver of an OLT may be delayed until just
before
a ranging response from an ONT is expected to be received.
The time to reset the receiver of the OLT may be based on a previous
successful ranging attempt, presumably before a rogue ONT was added to an
optical
distribution network (ODN), such as a passive optical network (PON). Such a
time
may be incremented in an iterative manner, for example, from minus 20 bit-
times to
plus 20 bit-times before or after the time to allow for variations. Each bit-
time may
be, for example, 6 nanoseconds at 155 megahertz (MHz). In other words, a time
to
reset a receiver may be changed to allow correct communication to an ONT when
a
rogue ONT is also present on the ODN.
When standard ranging fails to establish communication with an ONT, the
rogue tolerant ranging method according to an embodiment of the present
invention
may be used. If the rogue tolerant ranging method succeeds (i.e., an ONT is
successfully ranged), this indicates to an operator that one or more rogue
ONTs are
present and affecting the ODN. Such rogue ONTs can be identified and removed
at
a later time without further loss of service to other ONTs on the ODN. The
rogue
tolerant ranging method allows all ONTs on the ODN, including a rogue ONT, to
communicate with the OLT, even in the presence of the rogue ONT.
The rogue tolerant ranging method, unlike existing error detection techniques
(e.g., those described in the various PON protocols), detects and identifies
the
aforementioned-rogue ONT malfunctions. Moreover, no specialized test equipment
is used to overcome these malfunctions; the OLT can be configured in hardware,
software, or combination thereof, to test and adjust for the rogue ONT(s).
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FIG. 43 illustrates an example optical line terminal (OLT) 4300 to tolerate a
fault condition otherwise affecting ranging of an ONT. The OLT 4300 includes
an
OLT receiver 4305, determining unit 4310, time delay changing unit 4315, and
resetting unit 4320. At about a time the OLT receiver 4305 is expected to
receive a
ranging signal 4306 (e.g., a ranging response) from an ONT being ranged (not
shown) the OLT receiver 4305 is reset by the resetting unit 4320. In one
embodiment, the time the OLT receiver 4305 is reset by the resetting unit 4320
is
based on an equalization delay assigned to the ONT previously. In another
embodiment, the time the OLT receiver 4305 is reset by the resetting unit 4320
is
based on a time previously determined by a successful ranging attempt.
Whether a ranging attempt is successful is determined by the determining
unit 4310. The determining unit 4310 determines whether ranging is successful
by,
for example, measuring a no-input signal power level on a communications
pathway.
FIG. 44 is a diagram illustrating how a transmitted optical power level on a
communications pathway from a faulty ONT affects whether an ONT is successful
ranged by an OLT. A message diagram 4400a illustrates an exchange of ranging
signals or otherwise messages (e.g., a ranging grant (or ranging request) and
a
ranging response (or ranging cell)) between an OLT 4401 and an ONT 4402 during
a ranging window 4420. A transmitted power level versus time plot 4400b
illustrates the ONT 4402 transmitting a no-input signal power level 4403
during the
ranging window 4420. The no-input signal power level 4403 may be, for example,
a
power level of a rogue ONT or power levels of non-transmitting ONTs. A-
received
power level versus time plot 4400c illustrates the OLT 4401 receiving the no-
input
signal power level 4403, which has been integrated by an integrator 4404 in a
receiver (not shown) of the OLT 4401, as an integrated no-input signal power
level
4405.
The transmitted power level versus time plot 4400b indicates that the. no-
input signal power level 4403 may be constant during the ranging window 4420,
where the constant level may be a normal low level (e.g., -40dBm) or a faulty
high
level (e.g., between -30dBm and -20dBm, or higher). The integrated no-input
signal
power level 4405 ramps up from an integrated no-input signal power level at
time
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t;r,;tial 4410 to an integrated no-input signal power level at time tfnal
4415, over the
ranging window 4420.
In operation, while the no-input signal power level 4403 is being integrated
over the ranging window 4420, the OLT 4401 sends a ranging grant 4425 to 'the
ONT 4402. The ONT 4402, in turn, responds with a ranging response 4430. The
OLT 4401, having sent the ranging grant 4425, receives the ranging response
4430
from the ONT 4402 during the ranging window 4420 or it reports a ranging
error.
Typically, the receiver of the OLT 4401 is reset between adjacent upstream
timeslots to accommodate power levels which vary from ONT to ONT. During
16 ONT ranging, however, an upstream timeslot is effectively enlarged to
accommodate variability in supported fiber lengths, i.e., more than one
upstream
timeslot is used for the-ranging window 4420. For example, the ONT 4402 may be
located up to 20 kilometers away from the OLT 4401. To accommodate this
distance, the duration of the ranging window 4420 is set sufficiently long
enough to
allow the ONT 4402 located 20 kilometers away from the OLT 4401 to receive the
ranging grant 4425 and the OLT 4401 to receive the ranging response 4430.
When the duration of the ranging window 4420 is set for a long period of
time, the receiver of the OLT 4401 is not reset during this period of time. As
a
result, a no-input signal power level, such as power level of rogue ONT on the
ODN, have more time to be integrated by the receiver of the OLT 4401, thus
increasing the integrated no-input signal power level 4405.
As the received power level versus time plot 4400c illustrates, integrating
the
no-input signal power level 4403 over a long period of time causes the
integrated
no-input signal power level 4405 to-ramp (or increase). Consequently, over
time, it
may be more difficult to distinguish a zero-bit input signal (i.e., a zero
bit) from a
one-bit input signal (i.e., a one bit) possibly causing ranging errors and/or
may lead
to upstream communications problem(s)
Rather than using a typical ranging window, such as the ranging window
4420, to determine when to reset a receiver of an OLT, in one embodiment of
the
present invention, the receiver is reset at about a time a ranging response
from an
ONT is expected to be received. Changing the time the receiver is reset may be
referred to as a "dynamic reset." Through the use of the dynamic reset, the
amount
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of time a power level of rogue ONT is integrated may be limited, thereby
reducing
the adverse effects associated with integrating such a power level. In this
way, the
ranging techniques according to this and other embodiments of the present
invention
tolerate a fault_ condition otherwise affecting ranging of an ONT.
In some instances, however, resetting a receiver at about a time a ranging
response from an ONT is expected to be received by an OLT does not result in
successful ranging of the ONT. For example, a time between a time a ranging
response from an ONT is expected to be received by an OLT and a time a ranging
response from an ONT is actually received is large, possibly in tenms of a
time
window or relative to a sensitivity of a particular receiver with respect to
an amount
of power a rogue ONT adds to an optical fiber link. Consequently, despite
resetting
the receiver at about the time the ranging response from the ONT is expected
to be
received, a power level is integrated sufficiently long enough to affect ONT
ranging
adversely.
In another example, a time a ranging response from an ONT is actually
received occurs before a time a ranging response from the ONT is expected to
be
received. Again, despite resetting the receiver at about the time the ranging
response
from the ONT is expected to be received, a power level is integrated
sufficiently
long enough to affect ONT ranging adversely. In such instances, a time to
reset a
receiver is changed (described later in greater detail).
Additional techniques for determining whether ranging is successful are
described in reference to FIGS. 1-17.
Returning to FIG. 43, in an event the determining unit 4310 determines (e.g.,
via a ranging result 4307) ranging is unsuccessful; the determining unit 4310
communicates its results via a determination message 43311 to the time delay
changing unit 4315. The time delay changing unit 4315, in turn, changes the
time to
reset the receiver of the OLT, such as via a time to reset a receiver message
4316.
In one embodiment, the time delay changing unit 4315 is configured with an
adder (not shown) adapted to add a delay to the time when a ranging response
from
an ONT is expected to be received by an OLT. In another embodiment, the time
delay changing unit 4315 is configured with a subtracter (not shown) adapted
to
subtract a delay from the time when a ranging response from an ONT is expected
to
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be received by an OLT. In yet another embodiment, the time delay changing unit
4315 is configured with an incrementer (not shown) adapted to increment a
delay in
an iterative manner within a range of delays to delay the time to reset the
receiver of
the OLT and to compensate for variations in an equalization delay due to
physical
conditions expected to be experienced by an optical distribution network. In
this
way, the time to reset the receiver of the OLT is changed by the delay.
At the time to reset the receiver on the OLT, the resetting unit 4320 resets
the
OLT receiver 4305, such as via a reset signal 4321.
In FIG. 45, an optical line terminal (OLT) (not shown) with an OLT time
line 4505 ranges an optical network terminal (ONT) (not shown) with an ONT
time
line 4510. At a time Tinitial 4515, the OLT sends a ranging grant 4520 to the
ONT.
At a time Texpected 4525, a ranging response 4530 from the ONT is expected to
be
received by the OLT. In expectation, a receiver (not shown) of the OLT is
reset at a
time TieSC14545. In this example, the receiver is reset at about a time the
ranging
response 4530 is expected to be received. That is, the time Te,,pected 4525
and time
T,5C1 4545 occur about the same time.
In one embodiment, a receiver is reset at a time Trese, and disabled at a time
Tdisabied= Between the time Trset and the time Tdisabied is an expected
ranging response
time Tranging responsc, which is typically at least as long as a ranging
response message
or signal. Disabling the receiver at TdiSabied limits the effects of post-
integration by
an integrator (not shown) which may interfere with ONT ranging and/or may lead
to
upstream communications problem(s).
In this example, rather than at the time Teapected 4525, the OLT actually
receives the ranging response 4530 at a time Tactt,ai 4535. Between the time
Texpected
4525 and the time Tactuai 4535, in a typical optical receiver manner, the
receiver of
the OLT integrates a power level of a rogue ONT for a time Tiõtegrate 4540,
which
may extend further along the OLT time line 4505 to an upper bound of a typical
ranging window (e.g., a time equivalent to ranging an ONT 20 kilometers from
the
OLT). By not resetting the receiver of the OLT at the time Tinitiai 4515, but
at about
the time TexPected 4525 (e.g., at the time Treset 4545), in some embodiments,
the
amount of time the receiver integrates is limited or otherwise shortened to
the time Tintegrate 4540=
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FIGS. 46A and 46B are timing diagrams illustrating changing a time to reset
a receiver of an OLT in an event ONT ranging is unsuccessful.
In FIG. 46A, an OLT operating according to an OLT time line 4605a ranges
an ONT operating according to an ONT time line 4610a. At a time Tiõi,;ai
4615a, the
OLT sends a ranging grant 4620a to the ONT. At a time Texpected 4625a, a
ranging
response 4630a from the ONT is expected to be received by the OLT. In
expectation, a receiver of the OLT is reset at about the time TexPected 4625a.
Rather
than at the time Texpected 4625a, the ranging response 4630a is actually
received by
the OLT at a time Ta~tõai 4635a.
In this example, despite resetting the receiver at about the time Texpected
4625a
in a first ranging attempt, ranging is unsuccessful. In a second ranging
attempt, the
time to reset the receiver is changed by adding a delay 4640a to the time
Texpected
4625a. With the delay 4640a added, the receiver is reset at a time T,eSC,
4645a, and
ranging is successful. With the ONT successfully ranged, the time Trese, 4645a
may
be optionally stored. In others words, in an event ranging is successful, the
time
TfeSef 4645a is stored. As such, the receiver of the OLT in subsequent ranging
attempts is not reset at the time Texpeocod 4625a, but at the time
TfeSC14645a.
In an altemative embodiment, resetting a receiver of an OLT at about a time
a ranging response is expected to be received is based on a time which
resulted in a
successful ranging attempt previously.
In FIG. 46B, an OLT operating according to an OLT time line 4605b ranges
an ONT operating according to an ONT time line 4610b. At a time Ti,,itial
4615b, the
OLT sends a ranging grant 4620b to the ONT. At a time TeXpeaed 4625b, a
ranging
response 4630b from the ONT is expected to be received by the OLT. In
expectation, a receiver of the OLT is reset at about the time Texpe,td 4625b.
Rather
than at the time Texperted 4625b, the ranging response 4630b is actually
received by
the OLT at a time Tactual 4635b.
In this example, despite resetting the receiver at about the time Texpeoted
4625b in a first ranging attempt, ranging is unsuccessful. In a second ranging
attempt, the time to reset the receiver is changed by subtracting a delay
4640b from
the time Te,;Pec,ed 4625b. With the delay 4640b subtracted, the receiver is
reset at a
time Trese, 4645b, and ranging is successful. With the ONT successfully
ranged, the
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time T,ese, 4645b may be optionally stored. In others words, in an event
ranging is
successful, the time T,ese~ 4645b is stored. As such, the receiver of the OLT
in
subsequent ranging attempts is not reset at the time TeXPeald 4625b, but at
the time
T,,,e14645b.
In an alternative embodiment, resetting a receiver of an OLT at about a time
a ranging response is expected to be received is based on a time which
resulted in a
successful ranging attempt previously.
To ensure upstream communications sent from an ONT is received by the
OLT in a correct time slot, relative to upstream communications from other
ONTs,
data is delayed at least for an equalization delay before being sent.
Equalization
delays are assigned-to ONTs to equalize logical distances between the OLT and
ONTs, making every ONT appear equidistant from the OLT. Since physical
distances from the OLT vary from ONT to ONT, the equalization delays also vary
from ONT to ONT.
Based on an equalization delay assigned to a given ONT, a time a ranging
response from the given ONT is expected to be received can be calculated or
otherwise determined. As such, resetting a receiver about the time the ranging
response from the ONT is expected to be received may be based on the
equalization
delay for the given ONT.
However, an equalization delay for a given ONT varies, for example, as
physical conditions experienced (or expected to be experienced) by an optical
distribution network (ODN) change: For example, temperature variations cause
fiber optic cables to lengthen and shorten, effectively causing the ONT to be
further
away from or closer to an OLT in optical path distance. Accordingly, to ensure
the
OLT receives upstream communications in the correct time slot, an equalization
delay for a given ONT may be updated with some periodicity. Consequently, a
time
a ranging response from ai- ONT is expected to be received by an OLT and a
time a
ranging response from an ONT is actually received by the OLT may differ
throughout a day or from season to season. Generally speaking, to accommodate
such variations, a time to reset a receiver of an OLT may be delayed (or
advanced)
in increments.
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FIG. 47 illustrates an OLT operating according to an OLT time line 4705
ranging an ONT operating according to an ONT time line 4710. At a time
T;,,;t;aE
4715, the OLT transmits a ranging grant 4720 to the ONT. The OLT expects to
receive a ranging response 4725 from the ONT at about a time Terpe~ted 4730
based
on an equalization delay (not shown) known for the ONT. Due to variations,
however, the ONT transmits the ranging response after an equalization delay
Teectõai
4735, which differs from the equalization delay known for the ONT.
Consequently,
the OLT receives the ranging response 4725 not at the time Texpected 4730, but
rather
at a time Tnnai 4740. To accommodate such variations in an equalization delay,
a
time to reset a receiver of the OLT is changed.
In FIG. 47, a time to reset a receiver of the ONT Tfesrl 4745 is delayed for
one or more delay increments 4750a, 4750b...4750n, generally 4750a-n. In one
embodiment, a size (or duration) of the delay increments 4750 depends on a
transmission rate and is measured in "bit times." A "bit time" is an amount of
time
needed to eject one bit at a given rate of transmission. For example,
transmitting at
rate 155.52 Megabits per second (Mbps), one bit is ejected every 6
nanoseconds.
Thus, at 155.52 Mbps, one bit time is equal to 6 nanoseconds per bit. As
another
example, at I Gigabits per second (Gbps), one bit time is equal to l
nanoseconds per
bit.
In another embodiment, a size (or duration) of the delay increments 4750
depends on an overall system tolerance window. For example, the overall system
tolerance window may be defined or otherwise configured to be plus or minus
100
nanoseconds. Accordingly, a duration of each delay increment is some portion
of
the plus or minus 100 nanoseconds.
Continuing to refer to FIG. 47, the time Tfeset 4745 (i.e., the time to reset
the
receiver) is delayed for two delay increments, viz., 4750a and 4750b. That is,
from
the time TcXpected 4730 (i.e., the time the ranging response is expected to be
received),
two delay increments elapse before resetting the receiver. In this example,
the time
T,set 4745 is delayed for whole number multiples of the delay increments 4750.
In
another embodiment, a time to reset a receiver is delayed for something less
than
whole number multiples of delay increments, e.g., 1-1/2 delay increments, 2-
3/4
delay increments, and so forth.
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In FIG. 48A, due to a variation, transmitting a ranging response 4805a is
delayed for an actual equalization delay Tea,t,ai 4810a. Consequently, the
ranging
response 4805a is actually received at a time Tar.aj 4815a. Based on an
equalization
delay known to an OLT, however, the ranging response 4805a is expected to be
received at a time Texpected 4820a. In this instance, the time Tact,ai 4815a
occurs in
time before the time Texpected 4820a.
In a first ranging attempt, resetting a receiver of the OLT is advanced by n
number of delay increments from the time T,pec,ed 4820a, and the receiver is
reset at
a time Treset 4825a-1. In this example, the first ranging attempt is
unsuccessful, i.e.,
the ranging the ONT is unsuccessful. In an event ranging is unsuccessful in a
next
ranging attempt, the time to reset the receiver of the OLT is incremented
(i.e., a time
at which the receiver of the OLT is reset is incremented).
In a second -ranging attempt, a time at which the receiver of the OLT is reset
is advanced (not shown) by n-1 number of delay increments from the time
Texpectcd
.15 4820a. In this example, the second ranging attempt is unsuccessful. In a
third
ranging attempt, a time at which the receiver of the OLT is reset is advanced
by n-2
delay increments from the time Texpec,ed 4820a and the receiver is reset at a
time Treset
4825a-2. In this example, the third ranging attempt is successful.
In FIG. 48B, due to a variation, transmitting a ranging response 4805b is
delayed for an actual equalization delay Teactõei 4810b. Consequently, the
ranging
response 4805b is actually received by the OLT at a time Ta,:,,,a, 4815b.
Based on an
equalization delay known to an OLT, however, the ranging response 4805b is
expected to be received at a time Texpe,,ed 4820b. In this instance, the time
Teetõai
4815b occurs after the time Texpcctcd 4820b-
In a first ranging attempt, resetting a receiver of the OLT is advanced by
zero
number of delay increments from the time Terpected 4820b and the receiver is
reset at
a time Treset 4825b-1. In this example, the first ranging attempt is
unsuccessful, i.e.,
the ranging the ONT is unsuccessful. In an event ranging is unsuccessful in a
next
ranging attempt the time to reset the receiver of the OLT is incremented.
In a second and a third ranging attempt, the time to reset the receiver of the
OLT is advanced (not shown) by 1 and 2 number of delay increments from the
time
Z'expected 4820, respective. In this example, the second and the third ranging
attempt
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are unsuccessful. In a fourth ranging attempt, the time to reset the receiver
of the
OLT is advanced by 3 delay increments from the time Teõpected 4820b and the
receiver is reset at a time Trc5t14825b-2. In this example, the fourth ranging
attempt
is successful. With the ONT successfully ranged, the time Trese, 4825b-2 may
be
optionally stored. In others words, in an event ranging is successful, the
time Treset
4825b-2 is stored. As such, the receiver of the OLT in subsequent ranging
attempts
is not reset at the time Te,pe,,ed 4820, but at the time Treset 4825b-2.
In an altemative embodiment, resetting a receiver of-an OLT at about a time
a ranging response is expected to be received is based on a time which
resulted in a
successful ranging attempt previously.
FIG. 48A illustrates in an event a ranging response is actually received
before a time a ranging response is expected to be received (e.g., Texpected
4820a), a
time to reset a receiver (e.g., Trese, 4825a-1) is iteratively incremented by
advancing
the time to reset a receiver by n number of delay increments from the time
Texpec,ed.
FIG. 48B illustrates in an event a time a ranging response is actually
received
after a time a ranging response is expected to be received (e.g., Texpected
4820b), a
time to reset a receiver (e.g., Trese, 4825b-1) is iteratively incremented by
delaying
the time to reset a receiver by n number of delay increments from the time
Texpected.
In contrast to FIGS. 48A and 48B, in an event a ranging response is actually
received before or after a time a ranging response is expected to be received
(Texpected), a time to reset a receiver (Treset) is iteratively incremented by
both
advancing and delaying the time Trese, by n number of delay increments from
the
time Texpected.
In FIG. 49, transmitting a ranging response 4905 is delayed for an actual
equalization delay TeaC1ial 4910. Consequently, the ranging response 4905 is
actually received at a time Tae,,,ai 4915. Based on a known equalization
delay,
however, the ranging response 4905 is expected to be received at a time
Texpeeted
4920. To accommodate such variation a time to reset a receiver is changed by
iteratively incrementing a delay with a range of delays.
For purposes of describing this and other embodiments, delay increments
advancing a time to reset a receiver of an OLT (Tresc,) so that that the time
(Treset)
occurs in time before a time a ranging response from'an ONT is expected to be
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received (TeXceetea) are referred to hereinafter as "negative" delay
increments.
Conversely, delay increments delaying a time to reset a receiver of an OLT
(TreSC1) so
that the time Tresel occurs in time after the time Texpected are referred to
hereinafter as
"positive" delay increments. One skilled the art will readily acknowledge the
choice
of labels is arbitrary and is not intended to be limiting.
Cointinuing to refer to FIG. 49, a range of delay increments 4923 includes n
number of negative delay increments and m number of positive delay increments.
In
a first ranging attempt, the time to reset the receiver of the OLT is advanced
by n
number of negative delay increments from the time TeYpeaed 4920, and the
receiver is
reset at a time Trese, 4925-1. In this example, the first ranging attempt is
unsuccessful, i.e., ranging of the ONT is unsuccessful. In an event ranging is
unsuccessful; in a next ranging attempt the time to reset the receiver of the
OLT is
changed by incrementing to a next delay increment within the range of delay
increments 4923.
In an n's ranging attempt, the time to reset the receiver of the OLT is
advanced by zero number of negative delay increments from the time TeXpe.red
4920,
and the receiver is reset at a time TreSet 4925-2. In this instance, resetting
the
receiver at about the time the ranging response is expected to be received
does not
result in successful ranging.
In (n+2)'h ranging attempt, the time to reset the receiver of the OLT is
delayed by 2 positive delay increments from the time Te.,pected 4920, and the
receiver
is reset at a time Treset 4925-3. In this example, the third ranging attempt
is
successful. With the ONT successfully ranged, the time Treset 4925-3 may be
optionally stored. In others words, in an event ranging is successful, the
time Treset
4925-3 is stored. As such, the receiver of the OLT in subsequent ranging
attempts is
not reset at the time Te,,pected 4920, but at the time Treset 4925-3.
In an alternative embodiment, resetting a receiver of an OLT at about a time
a ranging response is expected to be received is based on a time which
resulted in a
successful ranging attempt previously.
FIGS. 48A, 48B, and 49 illustrate changing a time to reset a receiver in a
"forward" direction in time. For example in FIG. 48A, in a first ranging
attempt, the
time to resetthe receiver is advanced by n number of delay increments, and the
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receiver is reset at the time TfeSCt 4825-1. Then in a second ranging attempt,
the time
to reset the receiver of the OLT is advanced by n-1 number of delay
increments, and
the receiver is reset at the time Trcse14825-2. The time Treset 4825-1 occurs
before
the time Trese, 4825-2. One skilled in the art, however, will readily
recognize
embodiments of the present invention are not limited to this example.
For example, in a first ranging attempt, a time to reset a receiver of an OLT
is delayed by n number delay increments from a time a ranging response from an
ONT is expected to be received (Te,Pecced). In a second ranging attempt,
resetting the
receiver is delayed by n-I number of delay increments from the time TexPected,
and so
on. With each successive ranging attempt, a time to reset a receiver (Treset)
occurs
earlier in time. That is to say, a time to reset a receiver is changed in a
"backwards"
direction in time relative to the time TeXPected in successive ranging
attempts.
In another example, in a first ranging attempt, a time to reset a receiver of
an
OLT is delayed by n number of delay increments from a time a ranging response
from an ONT is expected to be received (Te,Peetea). In the case of n being
equal to
zero, the receiver is reset at about the time the ranging response from the
ONT is
expected to be received. In a second ranging attempt, resetting the receiver
is
delayed by n number of delay increments in one direction in time. In a third
ranging
attempt, resetting the receiver is delayed by n number of delay increments in
the
.20 other direction in time, and so on. With each successive ranging attempt,
a time to
reset a receiver (Treset) occurs either earlier or later in time. That is to
say, a time to
reset a receiver starts at a "middle time" and can be shifted relative to the
middle
time in either directions in time in successive ranging attempts.
In yet another example, in a first ranging attempt, a time to reset a receiver
of
an OLT is delayed by n delay increments from a time a ranging response from an
ONT is expected to be received (TeJC~,ted). In a second ranging attempt,
resetting the
receiver is delayed by n12 delay increments from the time TeXPeeted, and so
on. With
each successive ranging attempt, a time to reset a receiver (Treset) is
halved.
In still another example, in a first ranging attempt, a time to reset a
receiver
of an OLT (Treset) is delayed by any number of delay increments from a time a
ranging response from an ONT is expected to be received (Te,;pected). In a
second
ranging attempt, the time Trr-,C1 is delayed by any number delay increments
from the
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time Texpected, and so on. That is to say, the time to reset a receiver of an
OLT is
randomized.
In still yet another example, a time to reset a receiver of an OLT is delayed
from a time a ranging response from an ONT is expected to be received
(TeXpected) by
a delay which has been calculated or otherwise determined.
In FIG. 50, a'flow diagram 5000 illustrates ranging an ONT. Ranging the
ONT starts (5002). A receiver of an OLT is reset (5005) at about a time a
ranging
response from the ONT is expected to be received. By doing so, a fault
condition
affecting ranging of the ONT is tolerated, and traffic and communications are
uninterrupted by a rogue ONT. Ranging the ONT ends (5007). The ONT is ranged.
In FIG. 51, a flow diagram 5100 illustrates identifying a fault condition. A
ranging attempt using a standard ranging window is determined (5105)
successful or
not. If determined (5105) successful, there is no fault condition to be
identified, and
the flow diagram 5100 ends. If determined (5105) unsuccessful, however, in a
next
ranging attempt, a receiver of an OLT is reset (5110) at a time a ranging
response
from an ONT is expected to be received (TeXpeeted).
Whether the next ranging attempt is successful is determined (5115). If
determined (5115) successful, a fault condition is identified.and the flow
diagram
5 100 ends. If determined (5115) unsuccessful, however, in a next ranging
attempt, a
time to reset a receiver of an OLT (TfC5C1) is changed (5120). With the time
TreSe,
changed (5120), the receiver of the OLT is reset (5125) at the time Treset=
Whether the next ranging attempt is successful is determined (5130). If
determined (5130) successful, a fault condition is identified and the flow
diagram
5100 ends. If determined (5130) unsuccessful, however, the flow diagram
further
determines (5135) whether to continue changing the time Treset=
Whether the flow.diagram 5100 determines (5135) to continue changing the
time Treset may be limited by, for example, a number of instances configured
or
otherwise permitted. By way of example, the number of instances is limited to
20
and, as such, the time Treset is changed (5120) 20 times before the time
Trese, is no
longer changed.
In another example, the time Treset is changed (5120) until a range of times
is
tried or otherwise covered. By way of example, the time Treset is changed
(5120) by
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1 to 100 nanoseconds. That is, the time Treset is changed (5120) by 1
nanosecond in
a first ranging attempt, by 2 nanoseconds in a second ranging attempt, and so
forth.
The time Tr,set continues to change (5120) until the time Trcset is changed by
100
nanoseconds.
If the flow diagram 5100 determines (5135) not to continue changing the
time Treset, a fault coridition is identified and the flow diagram 5100 ends.
If
however, the flow diagram 5100 determines (5135) to continue changing the time
Trcsct, the time Tresct is incremented (5140). The flow diagram 5100 continues
and the
receiver of the OLT is reset (5125) at the time TreSet.
Changing (5120) the time Treset and resetting (5125) the receiver of the OLT
at the time Tn5t1 in a next ranging attempt continues until the flow diagram
5100
either determines (5130) that a next ranging attempt is successful or further
determines (5135) not to continue changing the time Treset. In either
instance, a fault
condition is identified.
In FIG. 51, the flow diagram 5100 illustrates incrementing (5140) the time to
reset a receiver of an OLT (Treset) so that in each successive ranging
attempt, the
receiver is reset (5125) at a later and later time. In an alternative
embodiment (not
shown), a time to reset a receiver of an OLT is decremented so that in each
successive ranging attempt, the receiver is reset at an earlier and earlier
time.
The above description referring to FIGS. 43-51 describes ranging an ONT
while tolerating to a fault condition. A fault condition of a continuous
stream of
light up a shared fiber from an optical network terminal (ONT) to an optical
line
terminal (OLT) may adversely affect ranging of the ONT by the OLT. In an
.example embodiment, an optical receiver of an optical line terminal (OLT) is
reset at
about a time a ranging signal from an ONT is expected to be received. Through
the
use of the example embodiment, an ONT can be ranged in the presence of a rogue
ONT causing the fault condition. Moreover, the example embodiment enables the
rogue ONT to be ranged in a presence of the fault condition and an Optical
Distribution Network (ODN), which includes the OLT and the rogue ONT, to
continue to support communications in a presence of the fault condition.
While this invention has been particularly shown and described with
references to preferred embodiments thereof, it will be understood by those
skilled
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in the art that various changes in form and details may be made therein
without
departing from the scope of the invention encompassed by the appended claims.
Although several embodiments are described in terms of optical elements,
other embodiments may be applied to other networks, such as wired or wireless
networks. For example, the OLT and ONTs may correspond to routers and servers
in an electrical network. In addition, although described as "cards" herein,
it should
be understood that PON cards, OLT cards, or ONT cards may be systems or
subsystems without departing from the principles disclosed hereinabove.,
It should be understood that elements of the block diagrams, network
diagrams, and flow diagrams described above may be implemented in software,
hardware, or firmware. In addition, the elements of the block diagrams and
flow
diagrams described above may be combined or divided in any manner in software,
hardware, or firmware. If implemented in software, the software may be written
in
any language that can support the embodiments disclosed herein. The software
may
be stored on any form of computer-readable medium, such as random access
memory (RAM),'read only memory (ROM), compact disk read only memory (CD-
ROM), and so forth. In operation, a general purpose or application specific
processor loads and executes the software in a manner well understood in the
art.
