Multiplex communications – Fault recovery – Bypass an inoperative switch or inoperative element of a...
Reexamination Certificate
1999-08-12
2003-12-16
Ton, Dang (Department: 2666)
Multiplex communications
Fault recovery
Bypass an inoperative switch or inoperative element of a...
C370S220000, C370S395100
Reexamination Certificate
active
06665263
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a VP (Virtual Path) protection system for use when an error occurs on an Asynchronous Transfer Mode (ATM) network, and more particularly to a VP protection system and a VP protection method for restoring many VPs at a time when errors occur in many VPs on the same link at the same time.
2. Description of the Related Art
When errors occur on a plurality of working VPs on an working (active) path at the same time, many control messages, including error messages and switching request messages, are generated for VPs. This results in heavy message-forwarding traffic among nodes in the switching section of the network.
To solve this problem, a, method for grouping a plurality of VPs into a Virtual Path Group (VPG) is known. For example, Japanese Patent Laid-Open Publication No. A-10-84362 discloses a method for providing an address table associating VPGs with VPs belonging thereto. In addition, ITU-T SG13 Recommendation Draft I. ps (issued in November, 1997) proposes OAM (Operation and Maintenance) cells for use as switching control messages for each VPG.
The conventional VP protection method will be described with reference to drawings.
FIG. 4
is a diagram schematically showing an example of an ATM network. This network is composed of a plurality of ATM nodes
101
-
104
. ATM nodes
101
and
102
are linked by physical link
111
, ATM nodes
102
and
103
are linked by physical link
112
, ATM nodes
101
and
104
are linked by physical link
113
, and ATM nodes
104
and
103
are linked by physical link
114
, respectively.
n working VPs passing through the ATM node
102
are set up between the ATM nodes
103
and
101
which are the endpoint nodes of a switching section on this network. These n VPs are grouped into an working VPG
121
. For the working n VPs between the ATM nodes
103
and
101
which are the endpoint nodes of the switching section, n standby (protection) VPs for which only a path is determined but no bandwidth is assigned are provided in advance. These n standby VPs are grouped into a standby VPG
122
.
Also, in the network configuration shown in
FIG. 4
, two message exchange channels are defined between the ATM node
101
and the ATM node
103
: one is a message exchange channel
123
from the ATM node
101
to the ATM node
103
and the other is a message exchange channel
124
from the ATM node
103
to the ATM node
101
.
If an error occurs on a physical link
111
in the configuration described above the ATM node
101
senses this error and sends a VPG switching request message
131
via the message exchange channel
123
.
Because only paths are set up but no bandwidth is allocated to the standby VPs of the standby VPG
122
, the nodes on the standby path via which the switching request message
131
is sent allocate bandwidth required by the standby VPs.
The switching request message
131
is sent from the ATM node
101
which is the switching-request message originating endpoint to the ATM node
103
which is the switching-request message receiving endpoint. During this period, the ATM node
101
and the intermediate ATM node
104
allocate bandwidth to the standby VPs.
After allocating bandwidth at the ATM node
103
, a VPG switching-response message
132
is sent through the message exchange channel
124
to the ATM node
101
via the intermediate ATM node
104
to notify that bandwidth has been allocated at all nodes on the standby path.
Upon receiving the switching-response message
132
, the ATM node
101
knows that the bandwidth resource has been allocated to the standby VPG. Then, the ATM node
101
switches all working VPs to standby VPs.
Referring to
FIG. 5
, the internal processing of a node during the above-mentioned protection processing will be described.
FIG. 5
shows the configuration of, and processing flow of control within, an intermediate node .(ATM node
104
in
FIG. 4
) on a standby path when conventional protection is performed with the use of VPG switching messages.
As shown in
FIG. 5
, an ATM node
200
comprises a VPG switching message receiving circuit
201
which receives grouped alarm messages or switching request messages, a VPG switching message sending circuit
202
which sends a VPG switching message to the next node, a VPG expansion circuit
203
which expands a VPG into individual VPs, a VP resource allocation circuit
204
which allocates resources to each VP, one or more node resource management circuits
206
-i (i=1, 2, . . . , n) which manage the allocation of resources of the entire node, a VP resource information management table
251
which stores therein the resource requirements for each VP, and a VPG configuration information management table
252
which stores therein information for identifying the VPs constituting the VPG.
The ATM node
200
forward,s a switching-request message
291
or a switching-response message
292
. When the switching-request message
291
arrives at the ATM node
200
, the VPG switching message receiving circuit
201
receives it, identifies that the message is issued to the VPG, and sends it to the VPG expansion circuit
203
.
The VPG expansion circuit
203
references the VPG configuration information management table
252
to expand the VPG specified by the switching-request message into the individual VPs constituting the VPG and then sends the identifiers of the individual VPs to the VP resource allocation circuit
204
.
The VP resource allocation circuit
204
finds the amount of resources required for each VP by referencing the VP resource information management table
251
and allocates the required node resources and network resources with the use of the node resource management circuits
206
-i (i=1, 2, . . . n).
After allocating resources to all VPs, the VP resource allocation circuit
204
sends the switching-request message
291
, either via the VPG expansion circuit
203
or directly, to the VPG switching message sending circuit
202
. The VPG switching message sending circuit
202
sends the switching-request message
291
to the next node.
The VPG switching-response message
292
is sent or received by the VPG switching message receiving circuit
201
and the VPG switching message sending circuit
202
.
Although the configuration of an intermediate node is shown in
FIG. 5
, it may be applied also to an endpoint node. For example, at a switching-request message sending endpoint node (ATM node
101
in FIG.
4
), the switching-request message
291
shown in
FIG. 5
is an error information message and the switching-response message is terminated at this node.
Also, a switching-request message receiving endpoint node (ATM node
103
in
FIG. 1
) sends a switching-response message instead of a switching-request message. The operation of this endpoint node is basically the same as that of the intermediate node shown in FIG.
5
.
As described above, the conventional VP protection method uses VPG node-to-node messages to reduce the amount of transfer messages. However, after receiving a message, the endpoint nodes and intermediate nodes that forward the VPG message must allocate resources, such as bandwidths and paths, to each VP of the VPG where an error occurred.
This requires the node to expand the VPG message into messages for the VPs and, after completion of processing for all VPs, to generate a VPG message again for transmission to the next node.
In this case, the node cannot forward the message to the next node until the processing of all VPs is completed, increasing the time needed for recovery from the error.
This problem will be described with reference to FIG.
6
.
FIG. 6
shows the switching sequence on the standby path when error recovery is performed with the conventional protection method in the network configuration shown in FIG.
1
.
As shown in
FIG. 6
, when the ATM node
101
detects an error in the working path, it first references the message issued to the VPG and then performs VP expansion processing
311
to expand the VPG into individual
Kawabata Mitsuru
Sasaki Shinobu
Dickstein Shapiro Morin & Oshinsky LLP.
Duong Frank
NEC Corporation
Ton Dang
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