Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1999-06-24
2002-06-04
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Plural
C385S016000, C359S199200
Reexamination Certificate
active
06400859
ABSTRACT:
FIELD OF INVENTION
The invention resides in the field of telecommunications networks of the type which use fiber optic rings. In particular, it is directed to a novel protection mechanism which finds applications in such telecommunications networks having matched nodes.
BACKGROUND OF INVENTION
Fiber optic rings are widely used for the high speed backbone for telecommunications networks. A bidirectional fiber ring is generally made of at least two optical fibers, one fiber for each direction, to realize a bidirectionality for better performance. For higher reliability and survivability, a bidirectional fiber ring is also provided with a working bandwidth and a protection bandwidth in each direction. These bandwidths are provided either by partitioning each fiber or by provisioning separate fibers. A ring, therefore, may have, two, four or more fibers and separate fibers or any partitions thereof can be set aside as the working and protection bandwidths. In practice, however, separate fibers are generally used for working and protection bandwidths for each direction. A failure in a node or in a path of a ring triggers ring switch from the working bandwidth to protection bandwidth. These bidirectional rings (four fibers or two fibers) is called the bidirectional line switched ring (BLSR for short). Optical signals are transmitted through a ring in SONET or SDH format or some such similar format.
FIGS. 1 and 2
illustrate a two fiber BLSR in normal operations and its protection switching mechanisms respectively. In
FIG. 1
, the connections between the individual network elements (NEs for short or often interchangeably called nodes in the art as well as in this specification) are bidirectional, a fiber
10
for one direction and a fiber
12
for the opposite direction, as shown by arrows. Each fiber is partitioned 50-50 in bandwidth providing working bandwidths
14
and
16
and protection bandwidths
18
and
20
. This provides a 50% protection capacity. At each NE, a desired traffic is dropped from the line traffic and/or added to it from its tributary. The NEs function as add/drop multiplexers which drops traffic destined to them but pass through the line traffic destined to other NEs. They also add traffic from their tributaries to the line traffic. The line traffic is a high speed traffic around the ring and the tributary traffic usually is a low speed local traffic. In the figure NE
1
and NE
4
are communicating with one another under normal conditions, using working bandwidths
14
and
16
. In
FIG. 2
, a failure
24
occurred between NE
2
and NE
3
. At NE
2
, the working bandwidths
14
and
16
are looped back onto protection bandwidths
20
and
18
respectively. At NE
3
, similar switches occur. At NE
1
and NE
4
, the tributary traffic is still added to and dropped off the working bandwidths. All the remaining NEs are switched to “through” mode. The switch-over between the working bandwidth and the protection bandwidth is called “ring switch” and is invoked by setting certain field in the overhead of the traffic.
FIGS. 3
illustrates a four fiber BLSR in the normal operations and the protection switching mechanisms. The working bandwidths
30
and
32
and protection bandwidths
34
and
36
are provided by separate fibers. This provides a 1:1 (100%) protection. If, for example, an interruption
38
occurs between NE
2
and NE
3
, working bandwidths
30
and
32
are looped back at NE
2
and NE
3
to protection bandwidths
34
and
36
respectively. All the remaining NEs loop through protection bandwidths.
There are different types of traffic demand patterns in the network and therefore there are different types of architectures to fit the variety of demand patterns. The different architectures need to interface each other but they come with different levels of protection, thus making interfacing them a complicated task. One known way of interconnecting two BLSRs is a technology known as the matched nodes.
The “matched nodes” is a technology known in the industry for interconnecting two rings with protection mechanisms.
FIG. 4
shows schematically an example of an integrated inter ring protection using the matched nodes between two BLSRs. In this example, one ring
50
is OC
192
BLSR and another ring
52
is a OC
48
BLSR. Network elements NE
1
-NE
7
reside in ring
50
and network elements NE
8
-NE
12
reside in ring
52
. Four separate fibers (working and protection in each direction, designated by w and p respectively) are shown in each ring but similar arrangement can be made in two fiber BLSR environment. The network elements in this illustration are nodes where tributary traffic is added to and/or dropped from line traffic. During provisioning, the primary nodes and secondary nodes are identified on both rings for various paths between any pair of network elements spanning two rings. Therefore, different paths between different NEs would have different pairs of primary and secondary nodes. In
FIG. 4
, for example, for a traffic over a path between NE
1
and NE
12
, the primary node are NE
6
and NE
8
and the secondary nodes are NE
3
and NE
10
. The primary node pair and the secondary node pair are connected bidirectionally by fibers which are usually of a lower speed. In this specification, the primary inter-ring connection therefore consists of a bidirectional primary inter-ring circuit and a pair of the primary nodes as do the secondary inter-ring connection of a bidirectional secondary inter-ring circuit and a pair of the secondary nodes. The inter-ring circuits are therefore in fact tributary at the primary nodes or secondary nodes. The path on the primary inter-ring circuit between primary nodes NE
6
and NE
8
is called the primary path
54
. The path in each direction between NE
6
and NE
8
by way of NE
5
, NE
4
, NE
3
, NE
10
and NE
9
is called the secondary path
56
.
The secondary path
56
is invoked when the primary inter-ring connection fails, that is to say, when either or both of the primary node (NE
6
or NE
8
) and/or the inter-ring circuit between the primary nodes fail. The primary and secondary paths are separately shown in the figure. The secondary path between the primary node and the secondary node on the same ring can be provisioned over either the working bandwidth or the protection bandwidth. Thus, primary nodes NE
6
and NE
8
have modules
70
and
72
respectively which perform transmission of traffic in either DCW (drop and continue on working) mode or DCP (drop and continue on protection) mode. In DCW mode, line traffic is dropped to the inter-ring connection and the same traffic is continued on downstream nodes toward the secondary node on the working bandwidth. In DCP mode, the traffic is continued on the protection bandwidth.
Primary nodes have service selectors that allow them to choose either the traffic forwarded from its secondary node via the high-speed connection (line traffic in the ring or secondary path) or directly received from the other ring via the low speed connections (primary inter-ring circuit or primary path). In the Figure, primary nodes NE
6
and NE
8
have service selectors
74
and
76
respectively for bidirectional operation.
The bandwidth for the secondary path is allocated for the sole purpose of protection in the case of the primary inter-ring connection (i.e., a failure in the primary path or in the primary node), thus limiting the ring's total capacity. Furthermore, any middle nodes through which the secondary path passes have no full add/drop capabilities. These conditions therefore reduce the overall capacity and capabilities of the ring. The invention addresses these problems which are associated with matched nodes.
SUMMARY OF INVENTION
Briefly stated, the invention resides in a fiber optic bidirectional line switched ring including a primary and a secondary nodes through which another fiber optic bidirectional line switched ring is connected by way of a primary path and a dedicated secondary path respectively. In accordance with one aspect, a bidirectional line switched ring incl
de Boer Evert
Pare Louis Rene
Phelps Peter William
Steele David Charles
Wilson Stephen
Font Frank G.
Mooney Michael P.
Nortel Networks Limited
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