Multiplex communications – Fault recovery – Bypass an inoperative station
Reexamination Certificate
1999-03-04
2003-02-25
Kizou, Hassan (Department: 2662)
Multiplex communications
Fault recovery
Bypass an inoperative station
C370S225000, C370S238000, C370S404000, C370S406000
Reexamination Certificate
active
06526020
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a ring network system and a protection method therefor. More particularly, the invention relates to a ring network system which performs a path connection by a transoceanic function and a protection method therefor.
Generally, a ring network system is constructed by connecting a plurality of node elements (hereinafter referred to as NEs) by work lines and standby lines for protecting the work lines. And, a logical path is achieved by those physical work lines and standby lines.
Now, reference is made to a ring network system having eight NEs N
1
-N
8
, as shown in FIG.
8
. In this ring network system, to send frame data from NE N
1
to NE N
3
, the frame data is sent sequentially through NE N
8
, NE N
7
, NE N
6
, NE N
5
, NE N
4
, and NE N
3
. In
FIG. 8
, a thick solid line shows a route R
8
used in this case.
Further, in
FIG. 8
, to NE N
1
, input work lines W
1
and W
4
, output work lines W
2
and W
3
, input standby lines S
1
and S
4
, output standby lines S
2
and S
3
, and tributary lines T
1
and T
2
are connected, respectively. And, in the shown construction, a frame is sent from NE N
1
to NE N
3
. In addition, NE N
3
has tributary lines T
3
and T
4
.
In brief, in the route R
8
in
FIG. 8
, the tributary line T
1
of NE N
1
is an ADD line, while the tributary line T
4
of NE N
3
is a DROP Line.
Each NE has functions such as shown in FIG.
9
. Referring to
FIG. 9
, each NE comprises a terminating circuit
4
i for terminating control signals called overhead (OH) or section overhead (SOH), an OH adding circuit
7
i
for adding new OH to a multiplexed signal, a line fault detecting circuit
80
for detecting a line fault, a cross-connect unit
3
, a CPU
10
for controlling them, and a memory unit
200
. On the other hand, the line fault detecting circuit
80
is provided in a photoreceiver circuit, not shown.
The CPU
10
performs the switching control of the cross-connect unit
3
by referencing a table stored in the memory unit
200
. Namely, if no fault occurs, it carries out the switching control of cross-connect unit
3
according to the normal path information
200
a
stored in the memory unit
200
. This allows the switching control of the cross-connect unit
3
to realize all routes between the NE per se and the other NEs in addition to the above described route R
8
.
On the other hand, if a fault occurs at any position in a ring network, a protection process is performed by referencing path information
200
b
for West Span, path information
200
c
for East Span, path information
200
d
for West Ring, path information
200
e
for East Ring, and path information
200
f
for through. For instance, if a fault A
7
occurs between NE N
6
and NE N
7
, as shown in
FIG. 10
, the above described route R
8
cannot be realized, because the frame cannot pass through that portion. Thus, a route R
10
, shown by a solid line in
FIG. 10
, is achieved instead of the route R
8
.
To realize this route R
10
, the switching control of the cross-connect unit is performed as follows. First, when a frame is added from NE N
1
, NE N
8
becomes through. Then, at NE N
7
, the East Ring for connecting the working line to the standby line is performed. This makes the route R
10
to turn back at NE N
7
. After the turning back, NE N
8
, NE N
1
, NE N
2
, NE N
3
, NE N
4
, and NE N
5
become through.
And, at NE N
6
, the West Ring for returning from the standby line to the original working line is performed. This allows the route R
10
to turn back at NE N
6
. After the turning back, NE N
5
and NE N
4
again become through. Finally, the frame is dropped from NE N
3
. The above protection process allows each NE to continue the sending and receiving of frame data even if a fault occurs in part of the ring network.
The above described protection process ensues that each NE can continue the sending and receiving of frame data. However, there is a disadvantage that the route R
10
shown by a solid line in
FIG. 10
forms a long bypass.
As a function for solving this disadvantage, there is a transoceanic function. This function is to achieve the shortest path without going toward the position of the fault A
7
, as shown in FIG.
11
. Namely, it is to realize a route R
11
from NE N
1
to NE N
3
, passing only NE N
2
, without passing through a long path like the route R
10
shown in FIG.
10
.
That is, when NE N
1
to NE N
8
, which are a plurality of (16 at maximum) of multiplexers, form a ring network in
FIG. 10
, the signals of work lines W
1
to W
4
are remedied by turning back them using the standby lines S
1
to S
4
at NE N
6
and NE N
7
on both sides of the fault A
7
in the conventional ring protection , as shown in FIG.
10
. On the other hand, for the transoceanic function, the signals are salvaged by making a direct connection from NE N
1
, the signal input point, to NE N
3
, the output point, with the shortest distance, without making a bypass, as shown in FIG.
11
.
As a specific switching process, in the conventional ring protection, through-switch is uniquely performed in which only the NE at the fault end performs a ring switch to turn back the work lines to the standby lines, with the other NEs releasing the standby lines for remedying the work lines and connecting the stand by lines on both sides. Namely, S
1
is connected to S
3
, and S
2
is connected to S
4
.
On the other hand, the transoceanic function requires a process in which, also at the NEs other than the NE at the faulty end, it is determined whether the fault has an effect on the ADD/DROP path of the local NE, and switching is performed if there is a path requiring a remedy. For this, an unconventional process is needed to always check the fault position, and apply a remedy according to the correlation between the fault position and the path. As a result, there is a disadvantage that the process becomes complex and the path switching time becomes longer.
SUMMARY OF THE INVENTION
The present invention was made to solve the above described disadvantages of the background art, and its object is to provide a ring network system in which the protection process has a shorter path switching time, a protection method therefor.
The ring network system according to the present invention is a ring network system in which, when a fault occurs, a path connection is performed by the transoceanic function for realizing the shortest path that does not go toward the fault position,
wherein each node comprises a cross-connect portion for switching the connections between paths to realize a ring network;
a table having previously stored therein the correspondences between the fault occurring positions and the path switching information for connecting the local node and all the other nodes by the path connection by the transoceanic function, if a fault occurs at the positions; and
a referencing portion for referencing said table in response to the occurrence of a fault to extract the path switching information corresponding to the fault occurring position,
whereby the switching control of the cross-connect portion is performed according to the path switching information extracted as a result of the referencing by the referencing portion.
The protection method for a ring network system according to the present invention is a protection method in which, when a fault occurs in a ring network, a protection process by the transoceanic function is performed for realizing the shortest path that does not go toward the fault position, the method comprising:
a referencing step for referencing a table having previously stored therein the correspondences between the fault occurring positions in the ring network and the path switching information for connecting the local node and all the other nodes by the path connection by the transoceanic function if a fault occurs at the positions, thereby to extract the path switching information corresponding to the fault occurring position; and
a step for performing the switching control of the cross-connect portion according t
Hoang Thai D
Kizou Hassan
NEC Corporation
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