Efficient support for VP/VC groups
View Patent ↗A method for supporting VP/VC groups in asynchronous transfer mode (ATM) switching systems that implement ATM automatic protection switching (APS). A source (SA) transmits traffic substantially continuously on two paths and a destination (SB), or sink, selects at any time one of the traffic from only one of the paths for further processing. The method includes creating a groups table having an entry for each of the two instances of every active VP/VC group's member set. Each entry indicates whether the cells for that instance of the member circuits of that VP/VC group should be forwarded or discarded. Each entry references a corresponding entry in the groups table by means of a pointer. The method includes accessing a relevant entry in the groups table when a cell for that circuit arrives, discarding the cell if the accessed value is “discard,” and forwarding the cell as specified in the specific lookup table entry for that circuit if the accessed value is otherwise. Protection switching for a group requires only changing the value of the corresponding two entries in the groups table, a single operation regardless of the number of member circuits in the group.
1. A method for supporting virtual path/virtual channel (VP/VC) groups in asynchronous transfer mode (ATM) switching systems that implement ATM automatic protection switching (APS) in which traffic flows from a source on two paths and a destination selects traffic from only one of the paths at a time for further processing, the method comprising:
creating a groups table, the groups table having an entry for each of the two paths of every active VP/VC group, each active VP/VC group having an associated set of member circuits, each entry indicating whether the cells for that path of that VP/VC group should be forwarded or discarded, each entry referenced by means of a pointer field;
accessing a relevant entry in the groups table when a cell arrives on one of the two paths, the relevant entry associated with the one of the two paths, the relevant entry including a status value; and
discarding the cell if the status value is indicative of a discard status or forwarding the cell if the status value is not indicative of the discard status.
2. The method of claim 1 , wherein forwarding the cell comprises:
maintaining a lookup table including a lookup table entry for each circuit in the set of member circuits of each VP/VC group for forwarding cells; and
forwarding the cell as specified in the lookup table entry for that circuit.
3. The method of claim 2 , wherein a number of supported groups is determined in part by a number of bits allocated to the pointer field associated with the circuit for the cell.
4. The method of claim 1 , wherein a value of zero in the pointer field of the groups table indicates that the corresponding VC circuit or VP circuit is not a member of any of the VP/VC groups, and that a forward/discard status of the respective circuit is stored in a lookup table entry associated with the circuit.
5. The method of claim 1 , wherein the groups table is implemented as part of a module of the switching system.
6. The method of claim 1 , wherein a number of supported VP/VC groups is determined in part by a size of the groups table.