Multiplex communications – Fault recovery – Bypass an inoperative channel
Reexamination Certificate
1995-06-22
2001-04-24
Kizou, Hassan (Department: 2662)
Multiplex communications
Fault recovery
Bypass an inoperative channel
C340S870030
Reexamination Certificate
active
06222821
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to distributed restoration of a telecommunications network in response to a failure therein and specifically relates to the normalization of the network after the fault has been repaired.
BACKGROUND OF THE INVENTION
A self healing network (SHN) distributed restoration algorithm (DRA) restores traffic that has been disrupted by a fault in a telecommunications network by finding an alternate route (alt route) to carry the traffic to bypass the fault. Such SHN DRA scheme is amply described by the aforenoted co-pending applications. In brief, the alt route is established by interconnecting a number of spare links connecting different nodes of the network so that traffic may be rerouted through those spare links. These spare links may be referred to as spare capacity and they are purposely added to the telecommunications network to provide the network the ability to perform restoration. But this spare capacity has to be somewhat limited due mostly to economic considerations. Thus if, after restoration, the network were to remain in the topology which includes the use of the spare links, the ability of the network to restore traffic due to other failures is curtailed. In other words, the spare capacity provides a safety margin for distributed restoration to take place. Yet once the spare capacity or some portion of it has been used, the safety margin could be diminished to the point that it no longer exists unless the topology of the network is restored to its normal state, i.e. prior to the failure, so that subsequent restorations may be effected with confidence for future failures.
Currently, when there is an outage due to a malfunctioned fiber, once the fiber is repaired, technicians have to manually reconnect at each of the cross-connect switches of the telecommunications network the different working and spare links. And the technicians at each of the cross-connect switches that might have been affected by the malfunctioned fiber need to refer to a pre-plan drafted in anticipation of the fault and follow instructions therein to connect/disconnect the various ports of the switch, in order to return the cross connect switch to its pre-failure state. Needless to say, this process is quite laborious and is subject to operator mistakes, not to mention requiring a substantial amount of repair time.
BRIEF SUMMARY OF THE INVENTION
To provide an automatic reconfiguration or reversion of the network to the topology it had prior to the occurrence of a fault, during the restoration process each operation performed by each of the nodes of the network is recorded by a central controller which may be an Operations Support System (OSS). A topology of the network may include the identification of all of the nodes of the network, the identity of the various ports of the cross-connect switch of the node, and how the various ports are cross-connected within each switch. The OSS further monitors any alarm signals from each node of the network.
When a fault occurs, and the custodial nodes that bracket the fault sense the fault alarm, distributed restoration begins. The process of the various steps of the restoration process are monitored by the OSS so that each connect/disconnect operation effected by each cross-connect switch is recorded. Consequently, since the establishment of an alt route requires both custodial nodes and tandem nodes, the operations of all of those nodes are recorded.
After the traffic is restored, to ensure that the spare capacity of the network is not diminished, the malfunctioned link, which may be in the form of a SONET optical carrier level 12 (OC-12) channel for example, is physically located and action to repair the link is undertaken. The repair of the malfunctioned link is also monitored by the OSS so that once the repair is finished, it will sense an alarm clearing signal from the now restored link.
Once the OSS is sure that there are no other malfunctioned links in the network, it scans its memory to find the custodial nodes by looking for nodes that had performed multiple, for example 2, connect/disconnect operations. The OSS furthermore retrieves from its memory data relating to tandem nodes that had performed a single operation for acting as a part of the alt route for rerouting the traffic. Since each operation is recorded and the identity of each of the reconfigured ports in each of the cross-connect switches is likewise recorded the OSS can effect an automatic process for reverting the topology of the network to its pre-failure or normal state by inverting the various operations. The nodes that had performed two operations are deemed to be the custodial nodes that bracketed the malfunctioned link. Those nodes that had performed a single operation for rerouting the traffic are deemed to be the tandem nodes of the alt route.
To revert the topology of the network to its state before the occurrence of the fault, the ports in each of the custodial nodes are reconfigured so that the now restored link is again to be used to route traffic between the two custodial nodes. The path of the thus restored original route is next verified to ensure its integrity. After the integrity of the reverted path has been confirmed by the verification process, the respective connections in each of the tandem nodes are disconnected so that the spare links that interconnected those tandem nodes for rerouting the traffic are once more restored and ready to be called upon for the next restoration in response to the next fault.
The present invention therefore has the objective of providing a system and method for automatically reconfiguring the topology of a telecommunications network back to its normal state after a distributed restoration due to a fault in the network, and the repair of that fault.
The present invention has yet another objective of providing a telecommunications network a 100% spare capacity reserve once a malfunctioned fiber has been repaired so that restoration of future faults are not hampered by lack of spare capacity.
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Bengston Lee Dennis
Russ Will
Sees Mark Wayne
Wagner Clinton Allen
Kizou Hassan
MCI Communications Corporation
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