At+t Corp.

Other

At&t Bell Laboratories

Wilhelm Kremer

Daniel Yousef Al-Salameh

Steven H Hersey

Nicholas Paul DeVito

Philip M Francisco

A pair of SONET rings (12' and 14') can be interworked by providing at least two gateways (16.sub.m-1 and 16.sub.m) that are shared by each of the rings. Each shared gateway has the capability of transferring a block of optical information resident in a prescribed time slot in an interchange frame associated with one ring to a time slot in an interchange frame associated with the other ring so the block reaches its intended destination in that ring.

Multi-ring SONET architecture having shared gateways daisy chained to

Misconnections between communications circuits in a bidirectional line-switched ring transmission system are essentially eliminated by deterministically squelching in adjacent ring nodes, i.e., loop-back-switching nodes, communications circuits terminated in failed ring nodes in the ring transmission system. The deterministic squelching is realized by provisioning the ring nodes with all active communications circuits including those passing through the node which are terminated in other ring nodes in the bidirectional line-switched ring transmission system. Then, when one or more adjacent ring nodes fail, all active communications circuits terminated in those failed ring nodes are squelched in the adjacent ring nodes, i.e., in the loop-back-switching ring nodes.

Apparatus and method for preventing communications circuit

Communications circuit connectivity between a bidirectional line-switched ring transmission system and another ring transmission system is continued in the presence of the failure of a first shared node for communications circuits between the ring transmission systems by employing at least one additional shared node for the communications circuits; provisioning one or more duplex communications circuits between the first shared node and the additional shared node; and selectively allowing the one or more duplex communications circuits between the shared nodes to be established in the bidirectional line-switched ring when a ring node in the bidirectional line-switched ring in the first shared node has failed.

Ring interworking between a bidirectional line-switched ring

Selective tributary switching is realized in a bidirectional transmission system by selectively switching, in accordance with the same rules governing the set-up and take down procedures of full line-switching, only that portion of the bandwidth of the particular line which has been provisioned to be line-switched. The remaining bandwidth can be left unprotected or, by for the first time combining line-switched ting functionality with path-switched ring functionality in the same ring transmission system, some remaining bandwidth can be path-switched. Furthermore, another degree of switching freedom is achieved in a four optical fiber bidirectional ring transmission system by selectively span-switching, but not ring-switching, specific bandwidth on the line. To this end, communications circuit provisioning information is provided in the ring nodes as to whether a particular communications circuit should be line-switched or not and, if not, whether it should be span-switched, path-switched or left unprotected.

Apparatus and method for selective tributary switching in a

The possibility of passing off apparent 'good' higher level digital signals that may include corrupted or failed lower level digital signals because of inter-ring grooming of the lower level digital signals from one path-switched ring to another path-switched ring employing at least a first shared node and a second shared node is minimized by dual feeding communications circuits from one path-switched ring to the other via the shared nodes and by provisioning at least one inter-ring groomed communications circuit from a secondary ring node of one of the shared nodes (secondary communications circuit) of a particular ring to be supplied to a primary ring node in the other shared node of the same ring. The at least one secondary communications circuit is obtained in the primary ring node and demultiplexed so that the lower level digital signals in the at least one communications circuit can be evaluated on a one-to-one pairwise basis with corresponding lower level digital signals in the corresponding at least one communications circuit (primary communications circuit) being supplied from the inter-ring grooming apparatus associated with the primary ring node. The the 'best' of the lower level signals in each are selected and are combined into a 'new' primary communications circuit which is dual fed in the primary ring node in one direction to its termination ring node and in the other direction through the secondary ring node to the termination ring node. transmission path. A selector in the secondary ring node is revertively biased to normally select the 'new' primary communications circuit to be supplied to the termination ring node. However, in the case of a primary communication circuit failure because of an interconnect or other failure in the primary ring node, the selector will then select the secondary communication circuit to be supplied to the termination ring node for the primary ring node. The provisioning of the primary ring node and the secondary ring is such that the demultiplexing to obtain the lower level digital signals, their evaluation and selection, and multiplexing only need to be done in the primary ring node and not in both.

Ring interworking between path-switched ring transmission systems

The possibility of passing off apparent 'good' higher level digital signals that may include corrupted or failed lower level digital signals because of inter-ring grooming of the lower level digital signals from a bidirectional line-switched ring to a path-switched ring and vice versa which employ first and second shared nodes is minimized by dual feeding communications circuits from the bidirectional line-switched ring to the path-switched ring and vice versa via the shared nodes. An inter-ring groomed communications circuit is provisioned from a secondary ring node in the line-switched ring of one of the shared nodes (secondary communications circuit) to be supplied to a primary ring node in the other of the shared nodes of the line-switched ring. A replica of the secondary communications circuit is demultiplexed to obtain the lower level digital signals, which are evaluated on a pair-wise basis with corresponding lower level digital signals from the primary ring node. The least corrupted of the evaluated lower level signals are selected to be combined into a new primary communications circuit which is to be inserted in the line-switched transmission path. An inter-ring groomed communications circuit is provisioned from a secondary ring node of one of the shared nodes in the path-switched ring to be supplied to a primary ring node in the other shared node of the path-switched ring. The secondary communications circuit is demultiplexed to obtain the lower level signals which are evaluated on a pair-wise basis with lower level signals from a corresponding primary communications circuit to determine which of the lower level signals are least corrupted. The selected least corrupted lower level signals are combined into a new primary communications circuit which is then dual fed in the path-switched ring primary ring node.

Ring interworking between bidirectional line-switched ring transmission

The possibility of passing off apparent 'good' higher level digital signals that may include corrupted or failed lower level digital signals because of inter-ring grooming of the lower level digital signals from one bidirectional line-switched ring to another bidirectional line-switched ring, employing at least a first shared node and a second shared node, is minimized by dual feeding communications circuits from one line-switched ring to the other via the shared nodes. An inter-ring groomed communications circuit is provisioned from a secondary ring node of one of the shared nodes (secondary communications circuit) of a particular ring to be supplied to a primary ring node in the other shared node of the same ring. Additionally, a replica of the secondary communications circuit is demultiplexed in the primary ring node to obtain the lower level digitals signals therefrom. Then, the lower level digital signals in the secondary communications circuit are evaluated on a pairwise basis with corresponding lower level digital signals in a corresponding communications circuit (primary communications circuits) being supplied from the inter-ring grooming apparatus associated with the primary ring node to determine the least corrupted signal in each pair. The least corrupted lower level signals are selected and combined into a 'new' primary communications circuit which is inserted in the primary ring node.

Communications circuit connectivity in a bidirectional line-switched ring transmission system is continued in the presence of the failure of a first ring node for communications circuits terminated in the ring node which are redirectable to an alternate (dual hubbing) ring node. The communications circuit are redirected by establishing a bidirectional communications circuit to the alternate ring node. In one example, redirection of the communications circuits is further realized by not squelching communications circuits terminated in the failed ring node in a ring node adjacent the failed ring node on one prescribed side which normally would have been squelched, while squelching communications circuits terminated in the failed ring node in a ring node adjacent to the other side of the failed ring node. This allows the redirectable communications circuits to be loop back switched so that they may be redirected to the alternate ring node. Then, the alternate ring node directly intercepts the redirected communications circuits. This is realized by providing provisioning information to the ring nodes which includes the identity of all communications circuits active in the ring and whether there is an alternate ring node to which any of the communications circuits may be redirected.

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Dracut, MA, United States of America

Wilhelm Kremer