Call routing through an access node shared by multiple networks by using a double-network identifier

1. A method of operating a communication network, the method comprising:

in a call processing system, receiving a query signaling message for a call indicating a called number;

processing the called number to determine a single-network identifier associated with the called number;

processing the single-network identifier to determine if the single-network identifier identifies an affiliated network that is affiliated with the communication network, and if the single-network identifier identifies the affiliated network, then selecting a double-network identifier indicating both the communication network and the affiliated network; and

transferring a response signaling message that includes the double-network identifier.

2. The method of claim 1 further comprising, in a network node, receiving and processing the response signaling message that includes the double-network identifier, and in response to the double-network identifier, routing the call from the network node to a shared access node.

3. The method of claim 1 wherein the query signaling message indicates an access node identifier and further comprising, in the call processing system, processing the access node identifier to determine if the access node identifier identifies a shared access node that is shared by the communication network and the affiliated network, and wherein selecting the double-network identifier comprises selecting the double-network identifier if the access node identifier identifies the shared access node.

4. The method of claim 3 further comprising, if the access node identifier does not identify the shared access node, then in the call processing system, transferring a different response signaling message that includes the single-network identifier associated with the called number.

5. The method of claim 4 further comprising, in the network node, receiving and processing the different response signaling message that includes the single-network identifier, and in response to the single-network identifier, routing the call to the affiliated network.

6. The method of claim 1 further comprising, if the single-network identifier does not identify the affiliated network, then in the call processing system, transferring a different response signaling message that includes the single-network identifier associated with the called number.

7. The method of claim 6 further comprising, in the network node, receiving and processing the different response signaling message that includes the single-network identifier, and in response to the single-network identifier, routing the call to another communication network identified by the single-network identifier.

8. The method of claim 1 wherein the called number comprises a toll-free number controlled by the affiliated network.

9. A method of operating a communication network comprising:

in a network node, receiving a call set-up signaling message indicating a called number and processing the called number to determine that additional routing information is needed, and in response, transferring a query signaling message indicating the called number and an access node identifier;

in a call processing system, receiving the query signaling message and processing the called number to determine a single-network identifier associated with the called number, and processing the single-network identifier to determine if the single-network identifier identifies an affiliated network that is affiliated with the communication network;

if the single-network identifier identifies the affiliated network, then in the call processing system, processing the access node identifier to determine if the access node identifier identifies a shared access node that is shared by the communication network and the affiliated network;

if the access node identifier identifies the shared access node, then in the call processing system, selecting a double-network identifier indicating both the communication network and the affiliated network, and transferring a response signaling message that includes the double-network identifier; and

in the network node, receiving and processing the response signaling message that includes the double-network identifier, and in response to the double-network identifier, routing the call to the shared access node.

10. The method of claim 9 further comprising, if the single-network identifier does not identify the affiliated network, then in the call processing system, transferring a different response signaling message that includes the single-network identifier associated with the called number.

11. The method of claim 10 further comprising, in the network node, receiving and processing the different response signaling message that includes the single-network identifier, and in response to the single-network identifier, routing the call to another communication network identified by the single-network identifier.

12. The method of claim 9 further comprising, if the access node identifier does not identify the shared access node, then in the call processing system, transferring a different response signaling message that includes the single-network identifier associated with the called number.

13. The method of claim 12 further comprising, in the network node, receiving and processing the different response signaling message that includes the single-network identifier, and in response to the single-network identifier, routing the call to the affiliated network.

14. The method of claim 9 wherein the called number comprises a toll-free number controlled by the affiliated network.

15. The method of claim 9 wherein the query signaling message and the response signaling message comprise session initiation protocol messages.

16. A communication network comprising:

a network node configured to receive a call set-up signaling message indicating a called number and process the called number to determine that additional routing information is needed, and in response, transfer a query signaling message indicating the called number and an access node identifier;

a call processing system configured to receive the query signaling message and process the called number to determine a single-network identifier associated with the called number and process the single-network identifier to determine if the single-network identifier identifies an affiliated network that is affiliated with the communication network;

if the single-network identifier identifies the affiliated network, then the call processing system is configured to process the access node identifier to determine if the access node identifier identifies a shared access node that is shared by the communication network and the affiliated network;

if the access node identifier identifies the shared access node, then the call processing system is configured to select a double-network identifier indicating both the communication network and the affiliated network, and to transfer a response signaling message that includes the double-network identifier; and

the network node is configured to receive and process the response signaling message that includes the double-network identifier, and in response to the double-network identifier, route the call to the shared access node.

17. The communication network of claim 16 wherein, if the single-network identifier does not identify the affiliated network, then the call processing system is configured to transfer a different response signaling message that includes the single-network identifier associated with the called number.

18. The communication network of claim 17 wherein the network node is configured to receive and process the different response signaling message that includes the single-network identifier, and in response to the single-network identifier, route the call to another communication network identified by the single-network identifier.

19. The communication network of claim 16 wherein, if the access node identifier does not identify the shared access node, then the call processing system is configured to transfer a different response signaling message that includes the single-network identifier associated with the called number.

20. The communication network of claim 19 wherein the network node is configured to receive and process the different response signaling message that includes the single-network identifier, and in response to the single-network identifier, route the call to the affiliated network.