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Cisco IP Telephony Troubleshooting Guide for Cisco CallManager Release 3.0(1)
© 2000 Cisco Systems, Inc. 73
Appendix C – Troubleshooting Case Study 3
Inter-Cluster Cisco IP Phone-to-Cisco IP Phone Calls
In the previous case studies, the call flow and troubleshooting techniques of an intra-cluster call
and a Cisco IP Phone call through a Cisco IOS Gateway to a phone hanging off of a local PBX
or somewhere on the PSTN have been discussed in detail. This case study examines a
Cisco IP Phone calling another Cisco IP Phone located in a different cluster. This type of call is
also known as an inter-cluster Cisco IP Phone call.
Sample Topology
The following is the sample topology is used in this case study. There are two clusters, each
having two Cisco CallManagers. There are also Cisco IOS Gateways and a
Cisco IOS Gatekeeper in place.
Inter-Cluster H.323 Communication
As you can see in the topology, the Cisco IP Phone in Cluster 1 is making a call to the
Cisco IP Phone in Cluster 2. Inter-cluster Cisco CallManager communication takes place using
the H.323 Version 2 protocol. There is also a Cisco IOS Gatekeeper for admission control. The
detailed explanation of the debug output and show commands, and the interaction between the
Cisco IOS Gatekeeper and Cisco IOS Gateway and Cisco CallManager devices can be reviewed
in the previous sections.
The call flow process is shown in the diagram below. The Cisco IP Phone can talk to the
Cisco CallManager via Skinny Station protocol, and the Cisco CallManager can talk with the
Cisco IOS Gatekeeper using the H.323 RAS protocol. The Admission Request message (ARQ)
is sent to the Cisco IOS Gatekeeper, which sends the Admission Confirmed message (ACF) after