Traffic engineering in bi-directional ring networks

1. In a communication system made up of network nodes arranged in multiple interconnected networks, including a bi-directional ring network having an inner ring and an outer ring, a method for traffic engineering, comprising:

defining the bi-directional ring network as a multi-access network for purposes of a routing protocol used in the system;

advertising constraint information to the nodes in the system outside the bi-directional ring network with regard to connections on the inner and outer rings between the nodes within the bi-directional ring network, the constraint information comprising a bandwidth constraint that is applicable to one of the inner and the outer rings and is associated with a protection mechanism comprising wrapping or steering of traffic flows between the inner and outer rings; and

routing a traffic flow from one of the nodes in the system outside the bi-directional ring network through the system in accordance with the routing protocol, so that the flow passes through the bi-directional ring network on at least one of the connections on one of the inner and outer rings that is selected responsive to the constraint information.

2. A method according to claim 1 , wherein each of the connections comprises a link between a source node and a destination node on one of the inner and outer rings, the link comprising one or more segments of the ring.

3. A method according to claim 2 , wherein advertising the constraint information comprises advertising a count of the segments that make up the link.

4. A method according to claim 1 , wherein each of the connections comprises a segment of one of the inner and outer rings that connects two of the nodes that are mutually adjacent.

5. A method according to claim 1 , wherein advertising the constraint information comprises advertising an indication that one of the inner and outer rings is to be selected to carry the traffic flow.

6. A method according to claim 5 , wherein advertising the indication comprises designating that a class of service to which the traffic flow belongs is to be routed over the selected one of the rings.

7. A method according to claim 1 , wherein the communication system comprises an autonomous system, and the nodes comprise Internet Protocol (IP) routers, and wherein the routing protocol comprises an Open Shortest Path First (OSPF) protocol.

8. A communication system, comprising:

a plurality of network nodes; and

communication links connecting the nodes so as to define multiple interconnected networks, including a bi-directional ring network having an inner ring and an outer ring,

wherein the nodes are adapted to route a traffic flow from one of the nodes in the system outside the bi-directional ring network through the system in accordance with a routing protocol used in the system, for purposes of which protocol the bi-directional ring network is defined as a multi-access network, and

wherein the nodes are adapted to advertise to the nodes in the system outside the bi-directional ring network constraint information with regard to connections on the inner and outer rings between the nodes within the bi-directional ring network, and to select, responsive to the constraint information, at least of the connections on one of the inner and outer rings over which the flow is to pass through the bi-directional ring network, and

wherein the constraint information comprises a bandwidth constraint that is applicable to one of the inner and the outer rings and is associated with a protection mechanism comprising wrapping or steering of traffic flows between the inner and outer rings.

9. A system according to claim 8 , wherein each of the connections comprises one of the links between a source node and a destination node on one of the inner and outer rings, wherein the one of the links comprises one or more segments of the ring.

10. A system according to claim 9 , wherein the constraint information comprises a count of the segments that make up the one of the links.

11. A system according to claim 8 , wherein each of the connections comprises a segment of one of the inner and outer rings that connects two of the nodes that are mutually adjacent.

12. A system according to claim 8 , wherein the constraint information comprises an indication that one of the inner and outer rings is to be selected to carry the traffic flow.

13. A system according to claim 12 , wherein the indication comprises a designation that a class of service to which the traffic flow belongs is to be routed over the selected one of the rings.

14. A system according to claim 8 , wherein the communication system comprises an autonomous system, and the nodes comprise Internet Protocol (IP) routers, and wherein the routing protocol comprises an Open Shortest Path First (OSPF) protocol.

15. A method according to claim 1 , wherein routing the traffic flow comprises routing the traffic flow from a first node on a first bi-directional ring network to a second node on a second bi-directional ring network responsive to the constraint information regarding the second bi-directional ring network.

16. A system according to claim 8 , wherein the nodes are adapted to route the traffic flow from a first node on a first bi-directional ring network to a second node on a second bi-directional ring network responsive to the constraint information regarding the second bi-directional ring network.