Note: Descriptions are shown in the official language in which they were submitted.
CA 02403908 2002-09-25
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FAIL TO POTS AItCI~ITECTIJ1~E
This invention relates to a method and system for decreasing the effect of
loss
of power or data path on telephone customer premises equipment, and more
particularly to
equipment connected to pair gain devices.
BACKGROUND OF THE INVENTION
Twisted pair copper loops are the physical transmission facility for various
types of signals from a telephone central office (CO) to telephony equipment,
such as analog
telephone terminals, facsimile machines and voiceband data modems, at a
customer's
premises. With increasing demand for additional telephony services, there is
commensurate
increasing demand for copper Ioop transmission facilities. However, demand for
additional
physical copper loops cannot always be satisfied since only a limited number
of copper loops
have been installed by telephone operating companies, typically averaging 1.2
loops per
residence. Therefore, when the demand in a given area exceeds the number of
installed
physical loops in that area, some customers cannot be provided with additional
services. This
problem is sometimes called "copper exhaust", and can cause frustration for a
customer and a
loss of potential revenue for the telephone operating company.
Several technologies, all of which multiplex multiple services (most often
voice or plain old telephone service -- POTS) onto a single copper pair and
generically
known as "pair gain" or sometimes also Digital Added Main Line (DAML), have
been
developed to solve this problem. Systems employing pair gain technologies
require customer
premises equipment (CPE) at the customer end (home, office, etc.) of the
copper loop that
communicates with special equipment at the service provider end of the copper
loop.
Typical pair gain system architecture is shown in FIG. 1. The system includes
a pair gain central office terminal (COT) 24 at the telephone central office
(CO) or at a digital
loop concentrator (DLC) remote terminal (RT) 12. The pair gain COT 24 is
connected to a
telephone switch line access peripheral or to a DLC 12 to receive multiple
voice signals,
usually by means of analog POTS interfaces. The multiple voice channels are
connected to
the pair gain COT device 24, which impresses a signal containing the
multiplexed voice
channels onto a single twisted pair copper loop 26. A pair gain CPE device 2~
receives the
multiplexed signal, separates the constituent voice channels, and provides
individual analog
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POTS interfaces for each voice channel to connect to customer terminals, such
as telephones,
facsimile machines, etc.
Because the pair gain CPE device 28 may require more power in order to
operate its circuitry than can typically be provided by an access peripheral
(or DLC RT) 12
line card 20, the additional power requirements may be satisfied by a power
supply 30 which
derives its power from the local alternating current (AC) mains. If a local
power outage
disrupts the AC main power, communication using the pair gain CPE 28 becomes
impossible
until the AC main power is restored. The disruption of telephone service is
problematic for
subscribers who are accustomed to telephone service being available despite
power outages.
This is especially true in the event of a life or security threatening
emergency situation.
Uninterruptable AC power supplies (UPS) are commercially available and can
provide AC power for a short time in the event of a local AC main power
outage. However,
the disadvantages of local UPSs are their purchase and maintenance cost, the
limited time
these devices can supply power, and the regular maintenance that is required
to ensure they
are operational in the event of a power outage.
A typical solution to the provision of uninterruptable power to a pair gain
device is to provide power from an UPS at the CO over the twisted pair copper
loop 28 by
means of a high voltage power supply 30 coupled onto the copper loop 28 at the
pair gain
COT device 24. In order to provide sufficient power through the electrical
resistance of the
copper loop 26 to the pair gain CPE 28, the power supply must impress.a high
voltage,
typically 130 volts, onto the loop. This solution is costly since it requires
special circuitry at
the pair gain COT 24 to generate and couple the high voltage supply to the
copper pair 26.
Such a high voltage is also potentially hazardous to persons who might come
into physical
contact with the copper loop 26.
BRIEF SUMMARY OF THE INVENTION
The present invention seeks to provide a system and method that allows a pair
gain CPE to be powered locally, which is more convenient, less costly, and
less hazardous
but also provides access to a primary POTS line during a local power failure
or loss of pair
gain COT or pair gain CPE function.
In accordance with this invention there is provided a system for providing at
least one service in a multiservice communication system, the system
comprising:
(a) a combiner for combining a plurality of services for delivery between a
source and a user along a common line;
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(b) a decombiner for recovering the plurality of services from the common
line;
(c) a detector for detecting a failure condition in at least one of the
combiner or the decombiner; and
(d) a switch responsive to the detected failure for bypassing the failed
combiner or decombiner to couple at least one service determined to be
critical between the
source and the user.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the preferred embodiments of the invention will
become more apparent in the following detailed description in which reference
is made to the
appended drawings wherein:
FIG. 1 is a schematic diagram of a general pair gain system
architecture;
1 S FIG. 2 is a schematic diagram of a system according to an embodiment
of the present invention; and
FIG. 3 is a schematic diagram of a system according to a further
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
In the following description like numerals refer to like structures in the
diagrams. Referring to FIG. 1, a general pair gain system architecture is
shown generally by
numeral 10. The system comprises an access peripheral or DLC 12 at a central
office (CO)
that includes common voice equipment 14 for connecting a public switched
telephone
network (PSTN) 16 to a plurality of single voice channels 18. The signals from
the voice
channels 18 are interfaced to respective standard copper pairs 22 by
respective line cards 20.
The signals on these copper pairs 22 are combined by a pair gain COT device 24
into a
multiplexed signal and interfaced to a single copper pair 26. A pair gain
customer premises
equipment (CPE) device 28 at the customer premises receives the multiplexed
signal from the
single copper pair 26 and de-multiplexes or separates it into the constituent
voice signals for
coupling to customer equipment such as standard analog telephone terminals,
facsimile
machines or analog modems. A high voltage source 30 is provided to or is
contained within
the COT pair gain device 24 and provides power to the CPE 28 via the single
copper pair 26.
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As described in the background above there are certain limitations with the
above
architecture.
Referring to FIG. 2, an end-to-end architecture for providing at least one
service in a multi-service communication system, according to an embodiment of
the present
invention is shown generally by numeral 40. In particular the system 40
automatically
enables POTS service during AC main power failure or pair gain system failure.
The system
40 comprises a pair gain device combiner 42 for combining a plurality of
services 45 for
delivery between a source 46 and a user 48 along a common line 50, a pair gain
device
decombiner 52 for recovering each of the plurality of services from the common
line 50, a
detector (not shown) for detecting a failure condition in the pair gain system
and a switch 54,
56 responsive to the detected failure for bypassing the failed combiner 42 or
decombiner 52
to couple at least one of the services which is deemed to be critical between
the source 46 and
the user 48.
Failure of the pair gain system may be due to a variety of reasons. These
reasons include the loss of loop synchronization between the transmitters and
receivers used
to communicate the combined services signal on the loop 50, a degradation of
the loop
transmission characteristics due to a physical fault or interference from
other signals, or
failure of the local power 58 at the CPE end 44.
There exists a multiplicity of methods for combining several service signals
into a combined signal and impressing that signal onto a twisted pair loop.
Without
diminishing the generality of the system description, if the service signals
are POTS
voiceband signals, one possible method involves digitally multiplexing digital
representations
of the voice signals. The voice signals may be -law or A-law encoded pulse
code
modulation (PCM) signals. The voice signals might be multiplexed into a higher
rate bit
stream and digital subscriber loop (DSL) technology used to transform the
combined bit
stream into a signal suitable for transmission on a twisted pair loop.
Examples of suitable .
DSL technologies include integrated services digital network (ISDI~,
asymmetric DSL
(ADSL), symmetric DSL (SDSL), and the like.
As illustrated in FIG. 2 a pair of services 45, servicel and service2, are
shown.
However, this architecture can be extended to any number of services. The pair
gain devices
42 and 52 (i.e., combiner and decombiner) may be implemented as
multiplexers/de-
multiplexers or other similar devices, all of which are standard devices known
in the art.
Referring to FIG. 3 a detailed diagram of the system 40 extended to four
POTS interfaces 62 at the CPE end 44 is shown generally by numeral 60:
(Similar
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components may be implemented at the CO end.) The system 60 is capable of
detecting a
failure condition at the CPE 44 and automatically connecting the POTS
terminals 66 to the
copper pair 50. The system 60 includes a bypass block 64 coupled from the
incoming copper
pair 50 to one or more of the plurality of telephone terminals 66 and a
failure detection block
68 coupled to the digital pair gain decombiner or demultiplexer 52 and the
bypass block 64.
An optional cut-off switch 70 is connected in series between the incoming
copper pair 50 and
the digital pair gain demultiplexer 52. This cut-off switch 70 may also be
activated by the
failure detect block 68 to prevent interference from the decombiner
transmitter 52 with the
POTS terminals 66.
Typically, the bypass block 64 may be implemented as a number of normally
closed relays. Thus under normal operational conditions the relays 64 are
energized via the
demultiplexer 52 so that the relay contacts are in the open position, allowing
the signals along
the copper pair SO to be interfaced to the demultiplexer 52, and the separated
POTS signals to
be interfaced to the respective telephone CPE 66. Under a failure condition
such as loss of
power of the demultiplexer 52', power to the relays in the bypass block 64 is
lost and the relay
contacts close, causing the telephone CPE 66 to be connected directly to the
copper pair 50,
bypassing the demultiplexer 52. Thus the CPE 66 operates as if only a single
POTS line is
available. Once power is restored to the demultiplexer 52, the relays are
again energized and
the bypass block 64 is disconnected.
The COT is also capable of detecting when a failure condition has occurred in
the demultiplexer at the CPE end 44 and thus processes any signals from the
CPE end as if a
single POTS line exists. Thus the architecture described above allows a bypass
to occur
when no power is available. The architecture can be extended to any number of
lines.
The optional cut-off 70 of digital pair-gain path may be implemented to avoid
interference. The need for this block 70 is dependent on the compatibility
between the DSL
or other signal used to carry the combined voice signals and the baseband POTS
signals of
the POTS terminals. In the case of incompatibility, this block 70 disconnects
the DSL or
other signal from the decombiner from the copper loop 50.
Optional low pass filters may be used when the optional cut off 70 is not
employed and DSL or other signals are still present on the copper loop 50.
This may be
required to avoid nonlinear demodulation in the telephone equipment 66 and
consequent
objectionable audible noise.
S
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In a further embodiment of the present invention the access peripheral 12 also
implements an architecture for redirection of voice traffic from the pair-gain
path to baseband
POTS path in case of pair-gain failure.
The present system may be applied equally efficiently to a pairgain COT 24
which receives voice as an analog signal, as to a pairgain COT which receives
voice as a
digital (PCM) signal.
A priority-based bypass may also be implemented in the pair gain COT 24
(and optionally CPE 28) to enable call continuation during a failure. This
capability allows
one of multiple conversations to continue uninterrupted when a failure occurs.
If more than
ZO one POTS line is active when a pair gain system failure occurs, the line
with an assigned
priority maintains its call. This is accomplished by enabling only the COT
(and optionally
CPE) bypass corresponding to the voice service line assigned the primary
priority.
As described above, a POTS to pair-gain interface according to one aspect of
the present invention allows any of the multiple pair-gain lines to be called
from the public
phone system while in fail-to-POTS mode when no other lines are active,
without the need
for hunt groups feature at the CO. This feature is implemented by allowing any
of the
incoming voice channels that are normally combined when pair-gain is active to
connect to
the baseband POTS service. This allows incoming calls to any of the lines as
long as no
other Iines are active.
Additional features may be implemented by the pair-gain system when using-a
fail to POTS system of the subject invention, which include: creating the
appearance of a
busy line when the pair-gain lines cannot be reached due to failure, creating
the appearance of
a busy line by generating an off hook indication for the inaccessible line,
maintaining a voice
channel back to public switched telephone network (PSTI~ when failure occurs
while phone
lines are active (this ensures that calls are not dropped unless the customer
end hangs up),
generation of "on-hold" tone back to caller so that the line does not go
silent suddenly when
failure occurs, and a "call waiting"-like option implemented at the line card
or CO end pair-
gain device allowing multiple PSTN lines to access the pair-gain fail-to-POTS
line
simultaneously. In the latter case, a tone is generated to the user indicating
that another call
is coming in. A hook-flash event (i.e., press on hook-switch for about 1
second) indicates the
switch to the other line.
It may be seen that with the architecture of the present invention, many new
features may be added to existing pair-gain systems heretofore unrealizable
under failure
conditions of existing pair gain devices.
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Although the invention has been described with reference to certain specific
embodiments, various modifications thereof will be apparent to those skilled
in the art
without departing from the spirit and scope of the invention as outlined in
the claims
appended hereto.
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