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In a redundant CallManager environment, abnormal call setup delay is observed for calls coming in through the VoIP IOS gateway

Core Issue

Delay issues are observed in an IP telephony environment with Cisco CallManager server redundancy and the CallManager cluster containing a publisher and a subscriber. Dial peers are configured on the H.323 voice gateway with preference commands. One of the VoIP dial peers points to the publisher and the other points to the subscriber. When the publisher is down, the dial peer to the subscriber takes over the outage. This set up works fine, except for the delay caused while switching between the dial peers. It takes around 15 seconds to switch over to the second dial peer.


To reduce the delay between the dial peers, use the voice class configuration and set the H.225 timeout to the minimum.

By default, the H.225 Transmission Control Protocol (TCP) timeout is 15 seconds.

To reduce the delay, configure the H.225 TCP timeout to three seconds.

Perform these steps:

  1. Create a voice class, as shown in this example:
    voice class h323 1 
    h225 timeout tcp establish 3
  2. Assign this voice class to dial peers, as shown in this example:
    dial-peer voice 17000 voip 
    preference 1 
    destination-pattern XXXX 
    voice-class h323 1

For more information, refer to these documents:

Voice Gateways

IOS gateways

Version history
Revision #:
1 of 1
Last update:
‎06-17-2009 10:10 PM
Updated by: