Note: Descriptions are shown in the official language in which they were submitted.
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NETWORK ARCHITECTURES WITH TRANSPARENT TRANSPORT
CAPABILITIES
BACKGROUND OF THE INVENTION
Field of the Invention
This invention is directed to architectures for a transport network of a
telecommunication system, and more particularly, to network architectures
using transparent transport capabilities.
Background Art
The rapid evolution of the technology in recent years has made the
optical fiber one of the most targeted transmission media, due mostly to the
high transmission rates available and reduced error rates.
The Synchronous Digital Hierarchy (SDH) specifies a basic rate of 155.52
Mb/s, which is called synchronous transport module level-1 (STM-1). The
smaller rate of 51.840 Mb/s is called synchronous transport signal level-1
(STS-1) and is the basic rate of the SONET (Synchronous Optical NETwork)
version of SDH. Higher rates (STS-N, STS-Nc) are built from STS-1, and
lower rates are subsets of this. An STS-N frame comprises an overhead (OH)
field with administration, operation, maintenance and provisioning
information, and a payload field with user information. The optical
counterpart corresponding to an STS-N signal is called OC-N. To
accommodate asynchronous signals from previous generations of transport
equipment, North America (SONET) and Japan base their sub-STS-1
multiplexing hierarchies on the DS-1 rate of 1.544 Mb/s, while Europe (SDH)
is based on the a 2.048 Mb/s rate. The level of synchronous multiplexing
hierarchies where the schemes are common occurs at the European basic rate
STM-1 and the North American rate STS-3. Thereafter, the three approaches
multiplex these rates in multiple integers, all being compatible with the
basic
rates. While the present specification describes and illustrates signals of
rate
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(or bandwidth) according to SONET networks, it is to be understood that the
invention is applicable also to other synchronous networks.
It is well known that the topology of a synchronous optical network
can have a linear point-to-point configuration or a ring configuration. A
linear configuration protects the traffic on a working fiber (W) by using a
protection fiber (P) which will carry the traffic if the working fiber is
interrupted. A "1:1" system has an equal number of working and protection
links, a "1:N" system has N working channels and one shared protection
channel. Since the protection fiber is idle most of the time, extra-traffic
(ET)
of lower priority may be transmitted over the protection fiber.
The ring topology permits the network to also recover automatically
from failures due to cable cuts and site failures. Currently, two types of
SDH/SONET rings are used, namely unidirectional path switched rings
(UPSR), and bidirectional line switched rings (BLSR). Both ring types support
unidirectional and bidirectional connections.
The UPSR is typically used in the access network and therefore is built
for lower rates, such as STS-3/STM-1, which are sufficient for access link
demands. These rings are provided with bidirectional connections between
nodes, yet the traffic flow is unidirectional. The signal is always present on
both working and protection fibers, therefore, the protection fiber cannot be
used to carry extra-traffic (ET).
The BLSR is typically used in the transport network, and therefore is
built to operate at higher data rates, like STS-48/STM-16. For a four-fiber
BLSR (4F-BLSR) the working and protection traffic flow on separate fibers,
each for one direction. For a two-fiber BLSR (2F-BLSR),the fibers between
adjacent nodes carry working traffic and also have protection capacity
allocated within them. Bidirectional traffic between two adjacent nodes takes
place in the working time-slots, and protection traffic is inserted in the
protection time-slots. Since for a BLSR configuration the protection timeslots
are only used during a protection switch, they can be used for lower priority
ET. Due to the working timeslots reuse capability, a BLSR always provides
CA 02261448 2001-07-19
the optimum use of bandwidth for a given traffic pattern. However, an
automatic protection switching (APS) protocol is necessary.
A traffic node is defined as the transmission equipment deployed at a site.
In practical configurations, a site may comprise equipment belonging to
different
networks co-located in the same operation center. Such scenarios are common in
big cities. There are many benefits to supporting large bandwidths on a single
piece of equipment. Reducing i_he amount of equipment at a site simplifies the
network management and also means fewer trips to a location for equipment
repairs and replacement. The k.ey benefit is lower equipment cost.
Telecommunications network providers are feeling the pressure of
upgrading the equipment to the level of the latest technologies, as users
demand
ever more capacity. That factor, along with the reality of fiber congestion in
the
network, is causing providers to search for a solution that will increase
capacity
without forcing them to deploy additional fibers.
For an existing linear system that is experiencing fiber exhaust on a given
span, the traditional solution is to replace the relevant equipment to obtain
a
higher line rate system. However, for a ring configuration, the line rate of
the
entire ring must be upgraded even if only one span is short of fiber. It is
thus
easy to understand why some network providers are asking for other options.
The add/drop multiplexer combines various STS-N input streams onto an
optical fiber channel. Transparent transport is defined herein as the ability
to
provide continuity of all payloads and associated overhead bytes necessary to
maintain a lower bit rate linear or ring system through a higher bit rate
midsection, while reducing the required number of fibers interconnecting the
sites. The lower bit rate linear c>r ring system operates as if it were
directly
connected without the higher b:it rate midsection. Description of a
transparent
multiplexer, referenced as "TMux", is provided in the co-pending Canadian
Patent Application No. 2,234,790, filed on April 15, 1998 by Martin et al.,
assigned to Northern Telecom Limited and entitled "Transparent Multiplexer/
Demultiplexer". A method for i:ransparently transporting higher rates signals
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over a mid-span is disclosed in the co-pending Canadian Patent Application No.
2,235,083, filed on April 17, 1998 by Martin et al., assigned to Northern
Telecom
Limited and entitled "Transparent transport".
In summary, transparency in this specification implies that the bytes of the
trib overhead are manipulated by the TMuxs such as to not require altering the
provisioning of the existing systems, to maintain their protection switching,
maintenance signalling, section/line/path performance monitoring, and to
provide sufficient information i=or fault isolation. For example, if the trib
rate is
OC-48 and the midspan rate is OC-192, one solution possible is to carry the
working (W) channels for all OC-48 trib systems on the OC-192 (W) channel, and
the trib protection (P) channels over the OC-192 P-channel, without OC-192
protection switching enabled (defined in the above patents as the "nailed up"
OC-192 option). In this arrangEnnent, a failure of the OC-192 W-channel would
trigger a span switch of all trib systems.
Eight OC-48 lines, or thirty OC-12/OC-3 lines can be consolidated over
the high rate midspan, as detailed in the above mentioned patent applications.
Bidirectional couplers may be used to further reduce the fiber count on the
high
rate span, i.e. from four to two fibers. It is to be noted that the bandwidth
efficiency provided, 20 Gb/s bi-directional over two fibers, is accomplished
without the transponders and tight tolerance transmitters and dense WDM
couplers necessary in the equivalent WDM solution.
The invention is not limited to OC-3/OC-12/OC-48 trib signals carried by
an OC-192 supercarrier, but it is also adaptable to other bit rates, in
accordance
with the hardware and software evolution of transport networks. Also, the
invention is not limited to equipping of only identical trib rates, it is
possible to
carry transparently trib signals of different trib rates over the high rate
span. The
input tribs described in this invention have the same rate for an easier
understanding of the general concept. In addition, the invention is not
limited to
SONET signals, and it can be applied to other synchronous transport
technologies.
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SUMMARY OF INVENTION ;
It is an object of the present invention to provide various architectures
for upgrading telecommunication networks, which address fiber exhaust on a
per span basis, without having to replace the equipment of all existing
tributary (trib) systems. With this invention, an entire ring system does not
have to be upgraded to a higher line rate due to fiber exhaust on a single
span.
The invention is applicable to linear configurations and to ring
configurations, such as OC-48 rings, although lower rate systems, such as OC-
12 and OC-3 may also be upgraded. As well, the invention is applicable to
higher rate rings, such as OC-192 2F-BLSR (two-fiber bidirectional line
switched ring), and 4F-BLSR, where the high rate midsection is OC-768, for
example.
It is another object of the present invention to provide a network
architecture for a telecommunication system that permits tributary channels
to be carried transparently over a high rate line, with no change in
provisioning of tributary systems.
Accordingly, the invention is directed to a telecommunications
network operating according to a synchronous transfer mode standard,
comprising a pair of transparent multiplexers (TMuxs) connected over a
bidirectional high speed span for transparently transporting high rate
traffic,
and a plurality (I) of bidirectional self-healing rings, each ring (Ki) having
a
ring rate Ri, and including at least two nodes (Ai, Bi) connected to each
other
and to the transparent multiplexers over a i-th W/P line for transporting
working and protection traffic in a forward direction, and a i-th P/W line for
transporting protection and working traffic in a reverse direction, wherein I
is
an integer, i is the index of a respective bidirectional self-healing ring,
and i E
[1, I], and the high rate is the sum of all the ring rates Ri.
The invention is further directed to a telecommunications network
operating in accordance with a synchronous transfer mode standard,
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comprising a transparent multiplexer (TMux) for connection into a high
speed sub-network, a plurality (I) of bidirectional self-healing ring, each
ring
(Ki) including a subtended node connected to the transparent multiplexer
over a i-th W/P line for transporting working and protection traffic in a
forward direction, and a i-th P/W line for transporting protection and
working traffic in a reverse direction at a ring rate Ri, wherein I, N are
integers, i is the index of a respective bidirectional self-healing ring, and
i E [1,
I], and the high rate is the sum of all the ring rates Ri.
Further, a transparent ADM for a telecommunications network
operating according to a synchronous transfer mode standard, at a high traffic
rate comprises a trib input port and a trib output port for respectively
receiving K input tribs and transmitting K output tribs, each trib of a
bandwidth Ri~ an add/drop port for adding and dropping L local tribs, a
transparent multiplexer for transparently multiplexing the K input tribs and
the add local traffic into an output high rate signal, and a transparent
demultiplexer for receiving an input high rate signal and demultiplexing
same into the K output trib signals and the L drop tribs.
The invention also comprises a telecommunications network
operating according to a synchronous transfer mode standard, comprising, a
plurality (J) of transparent add-drop multiplexers (ADM-T) connected in a
high rate bidirectional self-healing ring configuration over a high speed
span,
at each ADM-T~ site, a plurality (L) of nodes subtended by the ADM-T~ and
connected to the ADM-T~ over a 1-th W/P line for transporting working and
protection traffic in a forward direction, and a 1-th P/W line for
transporting
protection and working traffic in a reverse direction at a ring rate Rl, a
plurality (M) of bidirectional self-healing rings including the ADM-T~, each
ring (Km) including at least two nodes connected to each other and to the
ADM-T~ over a m-th W/P line for transporting working and protection traffic
in a forward direction, and a m-th P/W line for transporting protection and
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working traffic in a reverse direction at a ring rate Rm, wherein J, L, and M
are integers, j is the index of a respective ADM-T in the high rate
~idirectional
self-healing ring configuration, 1 is the index of a respective subtended
node,
m is the index of a respective bidirectional self-healing ring, and the high
rate
isLxRl+MxRm.
Further there is provided a telecommunications network operating
according to a synchronous transfer mode standard, comprising, a first ADM
and a second ADM connected in a main network over a high speed span for
transmitting a high rate signal including a main signal and a subsidiary
signal, a first traffic node (A) at the site of the first ADM and a second
traffic
node (B) at the site of the second ADM for communicating to each other over
the subsidiary signal, a first additional input/output port at the first ADM
for
transferring the subsidiary signal to and from the first traffic node, and a
second additional input/output port at the second ADM for transferring the
subsidiary signal to and from the second traffic node.
A basic advantage of this invention is per span relief for fiber exhaust
where no changes to existing systems are desired.
Another advantage is that a pair of TMuxs at the sites connected by the
high line rate span may be a less expensive solution than the WDM
(wavelength division multiplexing) approach for some network applications.
For example, only one OC-192 electrical repeater is needed on the high rate
span according to the invention, while four electrical repeaters are necessary
in the OC-48 WDM approach. The cost of four OC-48 repeaters is about 1.6
times the cost of one OC-192 repeater. In addition, the WDM approach to
accommodate higher rates on an existing network requires replacing the
initially installed transmitters with a set of tight tolerance wavelength-
specific
(e.g. 1533 nm, 1541 nm, 1549 and 1557 nm) transmitters, adding to the overall
cost of the upgrade.
Another advantage of the transparency is that there are no potential
mid-span meet problems with the TMux-to- trib system interface regarding
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protection or data communication protocols, which may be the case for
conventional Mux/trib system interfaces.
In this specification, the term 'nested ring node' is used for a traffic
node which transports tributary traffic transparently over the high speed line
to another nested ring node, where each nested ring node, although
physically located in the higher rate system, behaves as a stand-alone
tributary
rate ring node.
In this specification, the term 'subtended ring node' is used for a traffic
node which terminates tributary system traffic at that node, where the
subtended ring node, although physically located in the higher rate system,
behaves as a stand-alone tributary rate ring node.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features and advantages of the
invention will be apparent from the following more particular description of
the preferred embodiments, as illustrated in the appended drawings, where:
Figure 1A illustrates a basic "span-by-span" application of the
transparent multiplexer (TMux);
Figure 1B illustrates how the eight OC-48 2F-BLSR tribs of Figure 1A
are carried transparently over a linear 4F OC-192 span using a "nailed-up"
configuration (without protection for the OC-192 span);
Figure 2A illustrates a "ring" application of TMux as an OC-192 TMux
node;
Figure 2B illustrates how the four OC-48 2F rings of Figure 2A are
consolidated transparently for transmission over a OC-192 TMux ring;
Figure 3A illustrates an OC-192 ring/TMux node (ADM-T);
Figure 3B illustrates a ring configuration with TMuxs, where the
bandwidth over two spans needs to be increased;
Figure 3C illustrates an upgrade for the configuration of Figure 3B
using OC-192 ring/TMux nodes (ADM-T);
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Figure 4A illustrates a configuration with TMuxs before upgrade;
Figure 4B illustrates an upgrade for the configuration of Figure 4A,
where the bandwidth between all nodes has been increased using OC-192
ADM-T nodes in conjunction with bidirectional couplers;
Figure 4C illustrates an upgrade for the configuration of Figure 4A
using OC-192 ring TMux nodes (ADM-T), where the equipment count has
been reduced;
Figure 5A illustrates another configuration with TMuxs before
upgrade;
Figure 5B illustrates an upgrade for the configuration of Figure 5A
where the bandwidth between all nodes has been increased using OC-192 ring
nodes (ADM) in conjunction with bidirectional couplers;
Figure 5C illustrates an upgrade for the configuration of Figure 5A
using OC-192 ADM ring nodes, where the equipment count has been reduced;
Figure 6A illustrates a TMux-ring configuration before upgrade;
Figure 6B illustrates the configuration of Figure 6A upgraded to an OC-
192 2F ring with subtended nodes;
Figure 6C illustrates a further upgrade for the configuration of Figure
6B using OC-192 ring nodes where the equipment count has been reduced;
Figures 7A, 7B and 7C illustrate upgrade stages for a typical
backbone/spur system, showing another application of the transparent
transport according to the invention.
Figures 8A, 8B and 8C illustrate use of TMux configurations as interim
steps in upgrading of a ring to a higher bandwidth;
Figures 9A, 9B and 9C illustrate use of TMux configurations as interim
steps in upgrading of a ring;
Figures 10A and 10B illustrates how traffic is switched between the
principal and secondary nodes of Figure 9C; and
Figures 10C shows how traffic is carried between the principal and
secondary nodes of Figure 9C.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
In the example illustrated in Figure 1A, eight OC-48 2F-BLSRs have
traffic nodes 1, 2 ... 8 and 1', 2'.... 8', respectively, in two adjacent
sites A and B,
which could be two metropolitan areas with heavy traffic. Without TMuxs,
each ring would need a fiber span between sites A and B, resulting in sixteen
fibers between sites A and B. In order to reduce the fiber count, each site A,
B
was equipped with a respective transparent multiplexer (TMux) 100,101,
which results in all traffic for the OC-48 rings being carried over a high
rate 4F
midspan comprising fibers 9 and 10, each supporting bidirectional traffic at
OC-192 rate. The OC-192 protection is disabled in this configuration, but any
protection switching information on a respective trib system is transmitted
from the input span 11, 12, ... 18 to the output span 11', 12',... 18' on the
midspan 9, 10.
Figure 1B shows how the eight 2F OC-48 trib systems of Figure 1A are
carried transparently over the linear 4F OC-192 span using a 'nailed-up'
configuration. For a 2F-BLSR trib system protection type, the traffic can be
carried over either the OC-192 W-channel or the OC-192 P-channel without
OC-192 protection switching enabled (hereinafter called the "nailed up" OC-
192 option). As illustrated in Figure 1B, the forward channels for four OC-48
trib systems are carried in the forward direction on the forward fiber of
working (W) span 9, and the reverse traffic is carried on reverse fiber of (W)
span 9. Similarly, the forward channels for four more OC-48 trib systems are
carried in the forward direction over the forward fiber of protection (P) span
10 and over the reverse fiber of P span 10 in the reverse direction. Each
fiber
of the high-speed span carries a bandwidth of OC-192, resulting in a total
bandwidth over span 9,10 of 20 Gb/s. In this arrangement, a failure of either
the OC-192 W-channel or P-channel would trigger a ring switch for the trib
systems.
Figure 2A shows a "ring" application of the TMux according to the
invention where four OC-48 2F-BLSR rings 1 - 4 are connected to a TMux
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node 200 over spans 11, 11'; 12, 12'; 13, 13'; and 14, 14', respectively. Node
200
is in turn connected in an OC-192 ring over spans 9 and 10.
Figure 2B illustrates how traffic from the four OC-48 2F-BLSR rings of
Figure 2A are consolidated transparently for transmission over the OC-192
TMux ring. Since the trib rings are 2F-BLSRs, each bidirectional span 11 and
11' carries both working (W) and protection (P) traffic in the respective time-
slots. For the forward direction (W-E), TMux 200 consolidates the OC-48
working traffic received over fibers 11- 14 and transmits it over (W) fiber
9F.
Similarly, protection traffic received from fibers 11' to 14' is transmitted
over
(P) fiber 10F. In the opposite direction (E-W), traffic received from fibers 9
and
is demultiplexed onto fibers 11-14 and 11'-14', respectively. 0C-192
protection is again disabled in this configuration.
Figure 3A shows the block diagram of an OC-192 ring/TMux (ADM-T)
node. A transparent add-drop multiplexer 64 receives input tribs I1 to IK
from K ports 54 to 56, each connected to a tributary network. TMux 58 also
receives L local add signals A1 to AL from add/drop port 59. These signals are
transparently multiplexed into a supercarrier S which is output from port 57
into a high rate network, in this case an OC-192 ring. Similarly, TMux 58
receives high rate signal S' from the high rate network and demultiplexes
same into K output trib signals 01 to OK, which are then inserted in the
respective trib network through ports 54 to 56, each connected to a tributary
network. TMux also provides L local drop signals D1 to DL to port 59. Such a
node may be used for upgrading networks to higher rates, or for saving on
equipment, as shown next.
Figure 3B illustrates a configuration with eight OC-48 rings using
TMuxs 100 to 103. In this configuration, OC-48 nodes 1-5 are co-located with
TMux 100 in central office 29, nodes 1'-5' are co-located with TMux 101 in
central office 29', nodes 6'-10' are co-located with TMux 103 in central
office
30', and nodes 6-10 are co-located with TMux 102 at central office 30. A first
OC-48 ring 21 includes TMuxs 100 and 101, nodes 4', 6', TMuxs 103 and 102,
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and nodes 6 and 4. Similarly, OC-48 ring 22 comprises nodes 100,101, 5', 7',
103, 102, 7 and 5. TMuxs 100 and 101 are also connected in three OC-48 2F '
rings, a ring 23 also including nodes 1, 1'; ring 24, including nodes 2, 2';
and
ring 25 including nodes 3, 3'. Similarly, TMuxs 102 and 103 are connected
over ring 23' including nodes 8, 8', ring 24' including nodes 9, 9', and ring
25'
including nodes 10, 10'.
Each TMux consolidates the traffic from its five tribs as in the
configuration of Figure 1A, therefore spans 9,10, and 9',10' each carry a
bandwidth of 5 x OC-48, while spans 27, 28 and 2T, 28' carry 2xOC-48.
If due to customer demand more bandwidth is needed over the spans
27, 28 and 27', 28', TMuxs 100 to 103 can be upgraded to ADM-T nodes 200-203,
as shown in Figure 3C, and connected in an OC-192 4F ring 31, resulting in the
configuration of Figure 3C. No additional fiber needs to be deployed between
any sites.
In this way, the OC-48 traffic (both working and protection) on rings 23-
25 and 23'-25' is still carried transparently over the OC-192W channel. 0C-48
nodes 4 - 7 and 4' - 7' of rings 21 and 22, respectively, become subtended
rings
(multiple two-node rings), namely 4 and 5 are subtended by ADM-T 200, 4'
and 5' are subtended by ADM-T 201, 6' and 7' are subtended by ADM-T 203,
and 6 and 7 are subtended by ADM-T 202. This results in a used capacity of 4
x OC-48 on spans 9, 10 and 9',10', since nodes 4-7 and 4'- 7' only add/drop
STS-24 of working traffic each. One STS-48 only is used on spans 27, 28 and
27', 28'. As such, the configuration of Figure 3C results in three additional
STS-48s available on each of spans 27, 28 and 27', 28'.
Figure 4A illustrates sixteen OC-48 2F rings. The configuration uses
TMuxs 100 and 101 provided at sites 29 and 29' respectively, for transparently
transporting the traffic on four OC-48 rings 23 - 26 within an OC-192
supercarrier over span 9,10. Similarly, TMuxs 102 and 103 deployed at sites
29' and 30', respectively, transport the traffic on four OC-48 rings 32'-35'
within an OC-192 supercarrier over span 2T, 28', TMuxs 104 and 105 deployed
at sites 30' and 30, respectively, transparently transport the traffic on four
OC-
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48 rings 23' - 26' within an OC-192 supercarrier over span 9', 10', and TMuxs
106 and 107 deployed at sites 30 and 29, respectively, consolidate the traffic
on
four OC-48 rings 32 - 35 within an OC-192 supercarrier over span 27, 28. The
OC-192 spans have protection disabled.
The customers' requests for more bandwidth between all sites can be
addressed as shown in Figure 4B, where the TMuxs were upgraded to OC-192
ADM-T nodes, which are connected in two OC-192 4F rings 41, 42, which use
the same fiber spans 9, 10; 2T, 28'; 9', 10' and 27, 28. Reference numeral 37
illustrates a group of four 2:1 couplers. Eight such groups are necessary for
directing the traffic from the two ADM-Ts at a respective site over the high-
rate spans, for both forward and reverse directions. The OC-48 ring segments
between the sites involved are still carried transparently by the respective
supercarriers. It is apparent that no additional fibers were deployed between
any sites, and that four additional OC-48 tribs may be carried over ring 41,
and
42 as shown by the thicker lines.
On the other hand, if reduction of equipment is desired, the TMuxs at
each site could be replaced by one ADM-T node connected in an OC-192 4F
ring configuration 51, as shown in Figure 4C. 0C-48 ring segments are still
carried transparently. No additional fiber span needs to be deployed in the
configuration of Figure 4C, while four OC-192 TMux nodes are freed-up.
Figure 5A illustrates a first upgrade stage configuration with TMuxs. In
the initial stage (not shown) nodes 1, 1', 9, 9'; 2, 2', 10, 10'; 3, 3', 11,
11'; 4, 4', 12,
12'; 5-5', 13, 13'; 6, 6', 14, 14'; 7, T, 15, 15'; and 8, 8', 16, 16'; were
connected in
eight respective 2F OC-48 rings. As in the previous examples, nodes 1-8 are
located at site 29, nodes 1'-8' are located at site 29', nodes 9'-16' are at
site 30'
and nodes 9-16, at site 30.
In the configuration shown in Figure 5A, each site is provided with
two TMuxs, a TMux for transparently transporting the traffic for all eight OC-
48 rings to/from a neighbouring site. For example, TMux 100 and 101
consolidate the traffic between nodes 1-8 at site 29 and nodes 1'-8' at site
29'.
Each span 9, 10, carries transparently traffic at OC-192 rate in both
directions,
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with no protection enabled on the OC-192 span. Similar connections are
provided between sites 29' and 30', 30' and 30, and 30 and 29.
The next upgrade stage involves replacing the TMuxs with OC-192 ring
nodes 250 - 257 and connecting them into two OC-192 4F rings 51, 52. While
two sets of four 2:1 couplers 37 are necessary at each site, resulting in a
total of
32 x 2:1 couplers for accommodating the bidirectional nature of the traffic
and
for consolidating the traffic on four fibers, no additional fiber needs to be
deployed between the sites. The OC-48 nodes 1-8;1'-8'; 9-16; and 9'-16' are
connected as subtended rings (multiple 2-node rings). As each OC-48 trib
system uses at most a bandwidth of STS -24 of working traffic on the OC-192
node, each span 9,10, carries only a bidirectional STS-96 of working traffic.
This leaves a bidirectional STS-96 available over each ring and results in a
bandwidth of four STS-48s available around the two rings 51, 52.
Figure 5C illustrates another upgrade for the configuration of Figure
5A for savings on equipment. The eight TMuxs 100 to 107 are here replaced
with four OC-192 ring nodes 250, 252, 254 and 256, to obtain an 4F OC-192 ring
53. Each OC-192 ADM subtends eight OC-48 nodes, resulting in four OC-192
nodes being freed-up. No additional fiber and equipment were necessary.
Figure 6A illustrates how traffic on four 2F OC-48 rings is carried
transparently by an OC-192 configuration with four TMuxs 100 - 103. Each
TMux carries four 2F OC-48 rings, as shown in Figure 2A, and each span 10,
28', 10', and 28 carries an STS-192 between adjacent sites. An upgrade is
shown in Figure 6B where the TMuxs were replaced with OC-192 ring nodes
250, 252, 254 and 256 connected into a 2F ring 61. The OC-48 ring nodes are
now subtended (multiple two-node rings). No additional fiber and
equipment were necessary. This is an interim step to the upgrade of Figure
6C.
The next upgrade stage is shown in Figure 6C, where the outboard OC-
48 NEs were eliminated, so that 16 OC-48 ring nodes (4 x 4) were freed-up.
The OC-192 ring nodes 260, 262, 264 and 266, and the resulting ring 62 is a 2F
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OC-192 which supports the same trib rates and quantities as the original
subtended OC-48 ring nodes, as ring 61.
Figures 7A, 7B and 7C illustrate upgrade options for a typical
backbone/spur system, showing a variation of the TMux referred to as nested
trib rings. The system to be upgraded, shown in Figure 7A comprises an OC-
192 backbone network 42 deployed between ADM #1 and ADM #2. Terminal
TM #1 is connected to the backbone over a lower rate spur including a
regenerator 43, ADM #3 and a trib port in ADM #1, while terminal TM #2 is
connected to the backbone through a separate lower rate spur system through
ADM #4 and a trib port in ADM #2.
To improve the survivability of the spur networks, the network
provider would like to close the spurs into a ring configuration. A subtended
ring configuration is one option available without the TMux of the present
invention, as shown in Figure 7B. Two new routes are provided, R #1
between the sites of ADM #1 and ADM #4, and R #2 between terminals
TM#1 and TM #2. As well, an additional tributary, which acts in conjunction
with the existing tributary as an embedded ADM #5, must be added to ADM
#1, and terminals TM #1 and TM #2 have to be upgraded to ADM #6 and
ADM #7, respectively. The changes are shown in bold on Figure 7B.
Figure 7C shows a second option possible with TMux used in a nested
trib ring. R #1 is not necessary in this configuration, resulting in fiber
savings. The dotted line illustrates the channel carried by R #1 of Figure 7B,
which is now nested in part of the OC-192 line. The embedded ADMs #5 and
8 are not subtended ring nodes, but nested ring nodes, where their
interconnecting span is nested in the OC-192 line. Thus, by upgrading a
normal linear ADM chain to include a nested trib ring (Figure 7C), the
network operator achieves a more survivable collector network with only the
addition of a single new route (R#2) rather than two as in the case shown in
Figure 7B (R#1 and R#2).
Figures 8A-8C illustrate the use of TMuxs in an interim configuration
for upgrading an OC-48 2F ring 81 to an OC-192 2F ring 82. The OC-48 2F ring
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of Figure 8A includes initially nodes 240, 242, 244, and 246, which are OC-48
ring nodes. During the interim stage shown in Figure 8B, the traffic is re-
routed onto three TMuxs 100,101 and 102 to increase bandwidth on a per span
basis. Thus, OC-48 traffic is carried between nodes 240 and 242 over a high
speed span 9, while OC-48 traffic is carried between nodes 240 and 246 over
high speed span 27. No additional fiber has been deployed between nodes 240,
242, and 246, as is the case when TMuxs are used. In the final stage shown in
Figure 8C, the entire ring has been upgraded to an OC-192 2F by reconfiguring
TMux's to ring ADMs. 0C-48 ring nodes are now subtended, i.e. connected to
the respective OC-192 ring node as an OC-48 2F ring. Each span 9, 2T, 9' and
27 carries an OC-192 of traffic.
Still another example for illustrating use of TMux configurations as
interim steps for upgrading an existing ring is shown in Figures 9A-9C. 0C-48
and OC-192 2F rings were used for these examples, but rings of lower or
higher rates may be upgraded in a similar way.
The example of Figure 9 provides for two OC-48 2F rings 91 and 92,
connected by a tributary span 95 between nodes 246 and 241, co-located at site
29, and further connected by a tributary span 95' between nodes 244 and 243
co-located at site 29'.
One option, without using transparency, is to upgrade ring 91 to a OC-
192 ring by replacing the OC-48 ring nodes 240, 242, 244, and 246 with OC-192
ring nodes 250, 252, 254, and 256, as shown in Figure 9B.
Another option, shown in Figure 9C, is to upgrade ring 91 to an OC-192
2F ring 93, with a portion of the OC-48 ring 92 nested within it. This option
frees up low speed ADMs and the interconnect, and one fiber route, 10.
Traffic between nested ADMs 240 and 242 is carried over span 9', as shown by
dotted line.
Figures 10A and 10B illustrates how traffic is routed between ADMs 257
and 258, while Figure 10C expands on how the inter-ring traffic is carried
over
the OC-192 span between these nodes, as in the example of Figure 9C. 0C-192
transmitter/receiver T/R#1 of primary node 257 exchanges traffic with ADM
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250 (arrow A1), and with ADM 258 (arrow A3) of OC-192 ring 93 through OC-
192 T/R#2.
T/R#3 of primary node 257 is connected to ADM 246 (arrow B1), and to
ADM 258 (arrow B3) over OC-48 ring 92 through OC-192 T/R#2. TR#2
handles both OC-192 and OC-48 traffic for the respective ring 93 (arrows A3
and A2) or 92 (arrows B3 and B2), while T/R#4 handles both OC-192 traffic as
shown by arrows A1 and A2, and OC-48 traffic , as shown by arrows B1 and B2.
Switch S W directs traffic on the respective ring. Secondary node 258 operates
in a similar way.
The OC-48 traffic is carried over the working timeslots of span 9', using
half of the working bandwidth, as shown in Figure 10C. This maintains
independence of OC-48 and OC-192 protection. For inter-ring traffic, the
service selector is at the sink node, not at the principal node 257 as usual.
The
relationship between the principal node 257 and secondary node 258 is flipped
between the rings, similar to BLSR opposite side routing.
While the invention has been described with reference to particular
example embodiments, further modifications and improvements which will
occur to those skilled in the art, may be made within the purview of the
appended claims, without departing from the scope of the invention in its
broader aspect.
