Cisco Trunk Concepts

In addition to adding gateways to the CallManager configuration, trunks can also provide connectivity to outside devices. Trunks are seen by Cisco CallManager as logical links to other networks. These links have the ability to determine the location of an endpoint, but do not carry voice traffic. This underscores the major difference between trunks and gateways: Gateways can typically locate (or represent) an endpoint and carry the voice traffic to that endpoint; trunks only locate an endpoint. For example, you could create an intercluster trunk from your CallManager cluster containing 3XXX extensions to another CallManager cluster containing 4XXX extensions. When a user in your cluster (extension 3505) dials an extension in the other cluster (extension 4505), the local CallManager signals over the trunk to the remote CallManager. This signaling occurs to locate the IP address of extension 4505. After this IP address has been found, the audio path opens directly between the local extension 3505 and the remote extension 4505.

Your choices for configuring trunks in Cisco CallManager depend on whether the IP WAN uses gatekeepers to handle call routing and on the types of call-control protocols that are used in the call-processing environment.

Cisco CallManager Administration supports the following trunk types:

• H.225 trunk gatekeeper-controlled Use an H.225 gatekeeper-controlled trunk for toll bypass or for integration with an existing H.323 environment. The H.225 gatekeeper-controlled trunk enables Cisco CallManager to communicate with Cisco CallManager clusters and other H.323 devices registered to the H.323 gatekeeper. The H.225 gatekeeper-controlled trunk is not recommended in a pure Cisco CallManager environment, but it is required in a mixed environment with Cisco CallManager and Cisco CallManager Express or another third-party H.323 gateway. The H.225 trunk attempts to discover the other H.323 device on a call-by-call basis. If it discovers a device that understands intercluster trunk protocol, it automatically uses that protocol. If it cannot discover the other device, Cisco CallManager uses the standard H.225 protocol. To use this method, choose Device > Trunk and choose H.225 Trunk (Gatekeeper Controlled).
• Intercluster trunk gatekeeper-controlled The intercluster gatekeeper-controlled trunk enables Cisco CallManager to communicate with other Cisco CallManager clusters registered to an H.323 gatekeeper. It is recommended that you use the intercluster gatekeeper-controlled trunk only in deployments based entirely on Cisco CallManager. To use this method, choose Device > Trunk and choose Inter-Cluster Trunk (GateKeeper Controlled) in Cisco CallManager Administration.

  Tip

  Because the intercluster trunk format is Cisco proprietary, Cisco recommends using H.225 gatekeeper trunks wherever possible. The gatekeeper-controlled intercluster trunk option remains for backward compatibility with early CallManager versions.

• Intercluster trunk nongatekeeper-controlled In a distributed network that has no gatekeeper control, you must configure a separate intercluster trunk for each remote cluster that the local Cisco CallManager can call over the IP WAN. The intercluster trunks statically specify the IP addresses or hostnames of the remote devices. To use this method, choose Device > Trunk and choose Inter-Cluster Trunk (Non-GateKeeper Controlled) in Cisco CallManager Administration.

  Note

  Intercluster trunks (nongatekeeper-controlled) between Cisco CallManager clusters are unidirectional. You must configure trunks to and from the cluster you are connecting for the trunks to operate.

• SIP trunk Cisco CallManager Release 4.x supports a Session Initiation Protocol (SIP) trunk for interworking with a SIP network or gateways, but it currently does not allow SIP IP Phones to register directly with Cisco CallManager. To use this method, choose Device > Trunk and choose SIP Trunk in Cisco CallManager Administration.