Multiplex communications – Fault recovery – Bypass an inoperative switch or inoperative element of a...
Reexamination Certificate
1999-08-05
2004-01-06
Nguyen, Chau (Department: 2663)
Multiplex communications
Fault recovery
Bypass an inoperative switch or inoperative element of a...
C370S222000, C370S242000
Reexamination Certificate
active
06674714
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a transmission device. More particularly, the present invention relates to a transmission device which adapts to various network configurations in a synchronous multiplex transmission network.
2. Description of the Related Art
Because of an increase of traffic, the use of synchronous multiplex transmission which utilizes optical communications for high-capacity transmission is in high demand. Especially, a synchronous multiplex transmission system which has a capability of transmission line switching in case of transmission line failure and which can form a ring, such as SONET, is widely used from the viewpoint of supporting diverse network configurations and ensuring reliability of a network.
An ADM (Add/Drop multiplexer) device, for example, is used as a transmission node of a synchronous multiplex ring transmission network. The ADM device can access a desired VT channel in an STS signal, where STS is a channel hierarchy of SONET.
FIGS. 1A and 1B
are conceptual diagrams for explaining UPSR which is a transmission line switching system in a SONET ring network. UPSR, an abbreviation of Unidirectional Path Switched Ring, is an example of a system in which a path is switched and is recovered by selecting, at a receiving node, either of two path signals which are sent in two different directions over the synchronous multiplex transmission network from a sending node. In
FIGS. 1A and 1B
, each of a node A
1
, a node B
2
, a node C
3
, and a node D
4
is a node which constitutes a SONET ring, and
FIGS. 1A and B
show a case in which a signal enters the node A
1
and exits from the node C
3
.
In
FIG. 1A
, a signal which enters the node A
1
is sent along two routes, one of the routes going through the node A
1
, the node D
4
, and the node C
3
and another route going through the node A
1
, the node B
2
, and the node C
3
. Then, the signal from the route along the node A
1
, the node D
4
, and the node C
3
is selected under normal conditions at the node C
3
. A path in a route selected under normal conditions, such as the route along the node A
1
, the node D
4
, and the node C
3
in the case of
FIG. 1
, will be called a default path hereinafter.
As shown in
FIG. 1B
, if a fault occurs in a path between the node A
1
and the node D
4
, which fault will cause a communication interruption, the path is switched to a path in the route along the node A
1
, the node B
2
, and the node C
3
so that the communication continues. A path which is a destination of such a path switching from a default path, such as the path in the route along the node A
1
, the node B
2
, and the node C
3
, will be called a non-default path hereinafter. In addition, the above-mentioned capability will be called path protection switching hereinafter.
FIGS. 2A and 2B
are conceptual diagrams of BLSR in a SONET ring network. BLSR is an abbreviation of Bidirectional Line Switch Ring, and is an example of a system which carries out cross connecting on a synchronous multiplex ring transmission network and which restores communication by looping back a signal using a protection channel when a transmission line failure arises. In
FIGS. 2A and 2B
, each of the node A
1
, the node B
2
, the node C
3
, and the node D
4
is a node which constitutes a SONET ring, and
FIGS. 2A and 2B
show a case in which a signal enters the node A
1
and exits from the node C
3
.
As shown in
FIG. 2A
, initially, a signal which enters the node A
1
is sent to the node C
3
on the route along the node A
1
, the node D
4
, and the node C
3
. Then, when a transmission failure occurs between the node A
1
and the node D
4
, which transmission failure results in a communication interruption, the signal is transmitted through the node A
1
, the node B
2
, the node C
3
, the node D
4
, and the node C
3
by using a protection channel.
FIG. 3
shows, as an example, a system block diagram of a transmission device
5
which accesses a desired VT channel in any STS signal of SONET, and mainly shows a part for carrying out channel cross connecting. The transmission device
5
includes an STS cross-connecting part
10
for cross connecting an STS signal, a VT cross-connecting part
20
for cross connecting a VT signal, interface (INF) parts
30
1
-
30
n
, for inputting signals, and interface (INF) parts
40
1
-
40
n
for outputting signals. The STS cross-connecting part
10
includes STS TSI parts
11
,
12
,
13
for performing cross connection of an STS signal, STS PSW parts
14
,
15
for path protection switching in UPSR, and a selector (SEL)
16
for selecting either of a path accessed in the STS level or a path accessed in the VT level. The VT cross-connecting part
20
includes a VT SQL part
21
for performing VT squelch, a VT TSI part
22
for cross connecting a VT level signal, and a VT PSW part
23
for path protection switching in UPSR. Squelch is a process for inserting an alarm indication signal into an unrecoverable channel.
In
FIG. 3
, signals input from the INF parts
30
1
-
30
n
branch to STS level signals and VT level signals at a branchpoint
24
. The STS level signals enter the STS TSI part
12
, and are cross connected in terms of STS level, and, if selected at the SEL part
16
, the signals are output to the INF parts
40
1
-
40
n
through the STS PSW part
15
. The VT level signals are cross connected in the STS TSI part
11
at STS level, and enter the VT cross-connecting part
20
which cross connects the entered signals at the VT level. Then, through the TSI PSW part
23
, the signals enter the STS TSI part
13
which cross connects the signals, and, if the signals are selected at the SEL part
16
, the signals are output to the INF parts
40
1
-
40
n
. In addition, VT squelch is performed in the VT SQL part
21
in which an alarm indication signal (AIS) is inserted into a VT channel in which a misconnection occurs.
FIG. 4
is a conceptual diagram of a VT access ring for explaining the VT squelch.
FIG. 4
shows a BLSR configuration which has two fibers, an inside one and an outside one. Each of the inside line and the outside line has a protection channel and an active channel of BLSR. As shown in
FIG. 4
, a VT signal added at the node C
3
goes through the node B
2
and is dropped at the node A
1
. In this case, the squelch table of the node A
1
includes “2” as an STS level source node ID, “2” as an STS level destination node ID, and “3” as a VT level source node ID. If a failure occurs between an E point
6
and an F point
7
, STS level squelch will not be carried out because the node A can recognize the node B in the STS level. As for the VT level, squelch will be carried out for the VT channel signal which has the source node ID “3” in the corresponding squelch table because the node A can not recognize the node C. A VT path AIS is inserted into the VT channel for which squelch is carried out.
FIG. 5
is a block diagram of a conventional VT SQL part
21
for performing the above-mentioned VT squelch. A squelch table setting part
60
includes registers which accommodate 28 VT channels per each of STS channels
60
1
-
60
n
, where data setting to each register is performed by a control part
67
. “Far End Node ID”, that is, the node ID of the farthest node among connected nodes to which data can be transmitted is sent to each of SQL decision parts
62
1
-
62
n
. For example, in the network shown in
FIG. 4
, when a failure arises at the F point
7
, node ID “
4
” is sent from the node D to the node A. Each of the SQL decision parts
62
1
-
62
n
, determines whether VT squelch should be carried out or not on the basis of comparison between the “Far End Node ID” and the setting data in the squelch table setting part
60
. The result of the decision is stored in each of the latching parts
64
1
-
64
2
. Then, a VT path AIS is inserted into channels which are applicable for squelch insertion in a squelch inserting (INS) part
66
.
FIG. 6
is a block diagram of the STS
Isonuma Ritsuko
Mochizuki Hideaki
Hyun Soon-Dong
Katten Muchin Zavis & Rosenman
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