Multiplex communications – Fault recovery – Bypass an inoperative station
Reexamination Certificate
1999-04-27
2003-09-02
Ton, Dang (Department: 2661)
Multiplex communications
Fault recovery
Bypass an inoperative station
C370S223000
Reexamination Certificate
active
06614754
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a BLSR (bi-directional line switched ring) network of a SONET (Synchronous Optical Network), and more particularly to a BLSR network system having characteristics in the slot control.
In the Ring network, transfer of traffic is performed in a frame unit called, for example, a STS-1 (Synchronous Transport Signal-1). These frames are time-division multiplexed into a predetermined position of the time slot, then being transmitted. At present, as described in “SONET Automatic Protection Switching”, ANSI (American National Standards Institute, Inc.), T1.105.01, there exist a 2-Fiber BLSR and a 4-Fiber BLSR as the BLSR network.
Concerning overview of the BLSR network, the description thereof is given in, for example, “SONET BLSR Equipment Generic Criteria, Overview of the BLSR Architecture”, GR-1230-CORE, Issue Dec. 3, 1996, Bell Communications Research Inc., pp. 3-1 to 3-24, 6-3, and 6-15 to 6-20.
In the 2-Fiber BLSR, the respective nodes are connected by two optical fibers, and a capacity within the respective channels is divided into two areas and the one is used for a working function and the other is used for a protecting function. In contrast to this, the 4-Fiber BLSR is configured in such a manner that there are provided working channels and protection channels and the respective nodes are connected by four optical fibers.
Both of the 2-Fiber BLSR and the 4-Fiber BLSR are systems in which under normal conditions, the traffic is transmitted using the working channel, and when there occurs a failure or the like, the traffic is protected using the protection channel. Hereinafter, taking as an example a 4-Fiber BLSR of an OC (Optical Carrier)-48, the explanation will be presented. Also, hereinafter, the traffic is described as “path”.
FIG. 1
shows a configuration example of the BLSR network and an examples of use of the channels. In
FIG. 1
, reference numeral
10
denotes the entire system of the BLSR network. The BLSR network
10
includes optical fiber transmission lines
11
having a high signal transmission rate of, for example, 2.4 to 10 Gbits/sec and a plurality of nodes
12
. The BLSR network illustrated in
FIG. 1
includes six nodes (nodes A, B, C, D, E, and F).
With two fibers provided for each of the directions in the signal transmission, the optical fiber transmission lines
11
consist of bi-directionally four optical fibers. Concretely speaking, the optical fiber transmission lines
11
include a CW direction (i.e. a clockwise direction in the drawing) of working channel
13
and a CW direction of protection channel
14
, and a CCW direction (i.e. a counterclockwise direction) of working channel
15
and a CCW direction of protection channel
16
.
The plurality of nodes
12
are inserted into the optical fiber transmission lines
11
with a span placed therebetween. Each of the nodes
12
houses a lower-level network element (omitted in, the drawing) having a low signal transmission rate of, for example, 150 Mbits/sec or 600 Mbits/sec. The each of the nodes
12
performs an addition or a drop of the path (the STS-1) in the respective channels between the lower-level network element belonging thereto and the optical fiber transmission lines
11
. Accordingly, the nodes
12
are also referred to as ADMs (Add Drop Multiplexers).
The example illustrated in
FIG. 1
indicates that the STS-1 path, which is added at the node C and passes through the nodes D, E and is dropped at the node F, is transmitted using a time slot number #
1
of the CW direction of working channel
13
.
In the BLSR network system in
FIG. 1
, when there occurs a failure on only the working channel between, for instance, the node D and the node E, a path that is trying to pass through the failed span is transmitted using the protection channel.
FIG. 2
shows a configuration in this situation.
In
FIG. 2
, when there takes place a failure on the working channel
13
between the node D and the node E, the node D and the node E switch the path, which is contained in the time slot number #
1
that has been transmitted by the working channel
13
, so that the path will be transmitted using a time slot number #
1
of the protection channel
14
. This switching illustrated in
FIG. 2
is referred to as “Span Switching”.
Also, in the BLSR network system in
FIG. 1
, when there take place failures on both of the working channel
13
and the protection channel
14
between the node D and the node E, the path that is trying to pass through the failed span, as illustrated in
FIG. 3
, is caused to be looped at the node D back to the counterclockwise direction of protection channel
16
.
As illustrated in
FIG. 3
, when there take place the failures on both of the working channel
13
and the protection channel
14
between the node D and the node E, the node D loops and switches the path, which is contained in the time slot number #
1
that has been transmitted by the working channel
13
, so that the path will be transmitted in the counterclockwise direction using a time slot number #
1
of the protection channel
16
. At this time, the nodes C, B, A and F permit the time slot number of the protection channel
16
to pass through without interchanging it.
In the node E, the path is caused to be transferred from the time slot number #
1
that has been transmitted by the protection channel
16
to the time slot number#
1
of the CW direction of working channel
13
. Then, the path is dropped at the node F. The switching performed at the node D or the node E in
FIG. 3
is referred to as “Ring Switching”.
As is seen from the above-mentioned description, it is the nodes at the both ends of a failed channel (in the examples in FIG.
2
and
FIG. 3
, the node D and the node E) that execute the Span Switching or the Ring Switching. Also, as illustrated in
FIG. 3
, when the Ring Switching is executed, the nodes A, B, C and F enter a Full Pass Through state in which they permit the protection channel and K-byte, i.e. switching control information, to pass through.
Next, the explanation will be given below regarding a configuration of the nodes.
FIG. 4
illustrates a configuration of the node
12
. Since all the nodes on the BLSR network are of the same configuration, the configuration of any one node is illustrated as a representative. As described earlier, the node
12
is referred to as the ADM (Add Drop Multiplexer). In the
FIG. 4
, the node
12
leads in the following: The four channels as Fiber Channels (channels for the Ring), i.e. the CW direction of working channel
13
, the CW direction of protection channel
14
, the CCW direction of working channel
15
and the CCW direction of protection channel
16
, and an Add Channel
27
for adding path transmitted from the lower-level network element
12
-
1
, and a Drop Channel
28
for dropping path so as to output it to the lower-level network element
12
-
1
.
An optical signals inputted from another node is received by an optical receiver (R)
21
, and is inputted into an overhead processing unit
23
so as to undergo an overhead processing. The path the overhead of which has been removed is then inputted into a cross connect unit
20
. The cross connect unit
20
performs a TSI (Time Slot Interchange) and a TSA (Time Slot Assignment) of the high rate-side path (the OC-48) and the low rate-side path (the STS-1), and the path inputted therein is divided into the respective directions in the frame unit of the STS-1.
The paths thus divided are each multiplexed, and undergo the overhead processing at the overhead processing unit
23
, and are converted into optical signals by an optical transmitter (T)
22
, then being outputted from any one of the CW direction of working channel
13
, the CW direction of protection channel
14
, the CCW direction of working channel
15
, the CCW direction of protection channel
16
and the Drop Channel
28
.
For instance, in the configuration illustrated in
FIG. 1
, the STS-1 path is added at the node C from the lower-level network elemen
Kimura Mitsunobu
Mori Takashi
Obayashi Seigo
Takahashi Masatoshi
Usuba Keiji
Ton Dang
Wilson Robert W.
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