Gatekeepers can provide the same call routing and CAC functionality for CallManager. You can use gatekeepers with CallManager between CallManager clusters in a pure IP Telephony network or in hybrid networks with CallManager clusters and voice gateways that are interfacing to PBX systems.
Configuring a CallManager Gatekeeper Trunk
You can set up CallManager to use a gatekeeper as follows:
Define the gatekeeper to CallManager.
Figure 17-3. Defining a Gatekeeper to CallManager
Set up the actual trunk to the gatekeeper.
Enter the zone name.
Figure 17-4. Defining a Gatekeeper Trunk on CallManager
At this point, the trunk should be registered to the gatekeeper and ready for use. You can verify this by using the show gatekeeper endpoints command on the gatekeeper, as shown in Example 17-13.
You can provide redundancy on the trunk by assigning up to three subscriber servers to the CallManager redundancy group that is associated with the device pool assigned to the trunk. This configuration causes all servers in the redundancy group to register with the gatekeeper. However, the H.323 trunk name that is used for the h323_id has a suffix of _n, where n is the node number of the CallManager server in the cluster. This ID is assigned automatically and cannot be changed.
This feature provides redundancy without adding administrative complexity. You configure a single trunk, but the gatekeeper registers multiple trunks, one from each subscriber in the CallManager redundancy group.
After you have created the trunk, set up CallManager to use the gatekeeper trunk for specific dialed numbers.
Figure 17-5. Associating a Route Pattern to the Gatekeeper Trunk
Cisco also recommends that you use the arq reject-unknown-prefix gatekeeper configuration command to prevent potential call routing loops that might occur across redundant CallManager trunks. If a called address does not match any of the known zone prefixes, the gatekeeper attempts to hairpin the call back through the originating gateway without arq reject-unknown-prefix configured. This action might cause loops in a CallManager environment with multiple trunks active to the gatekeeper.
CallManager does not support dynamic zone prefix registration. You must manually code zone prefixes on the gatekeeper for CallManager destinations.
You can verify proper operation and troubleshoot call routing problems in the same manner as with any registered H.323 gateway. CallManager uses the same RAS messaging format for call admission. For more information, see the "Troubleshooting Gatekeepers" section earlier in this chapter.
Part I: Voice Gateways and Gatekeepers
Gateways and Gatekeepers
Part II: Gateways
Media Gateway Control Protocol
Session Initiation Protocol
Connecting to the PSTN
Connecting to PBXs
Connecting to an IP WAN
Influencing Path Selection
Configuring Class of Restrictions
SRST and MGCP Gateway Fallback
Using Tcl Scripts and VoiceXML
Part III: Gatekeepers
Part IV: IP-to-IP Gateways
Cisco Multiservice IP-to-IP Gateway
Appendix A. Answers to Chapter-Ending Review Questions