Switchback to Call Agent (CUCM): H.323 and MGCP Approach

One topic is ‘HOT’ on the discussion forums now a days and that is how MGCP and H.323 gateway switchback to backup CUCM when primary is down or switchback to primary CUCM when it’s up again. I have tested some scenarios on my lab and the following procedures can be followed for such requirements:

For H323 GW

The command ‘h225 timeout tcp establish x’ plays the roll here within dial-peers. If any call agent goes down while in a call, after configurable number of seconds if searches other dial-peers with the same destination-pattern configured and switchback to that dial-peer.
voice class h323 1
h225 timeout tcp establish 3
dial-peer voice 1 voip
destination-pattern 3…
voice-class h323 1
session target ipv4:SUB
no vad
dial-peer voice 2 voip
destination-pattern 3…
voice-class h323 1
session target ipv4:PUB
no vad
preference 1


Either manually configure this on gateway (if we don’t download the configuration with the command ccm-manager config):
ccm-manager switchback immediate

Or configuring it on the MGCP GW page at CUCM (must need the command ccm-manager config):

“Switchback Timing* = Immediate”,  It’s ‘Graceful’ by default.

This is just to mention that: you can switchover to backup Call Agent manually with the command ‘ccm-manager switchover-to-backup’ if the command ‘ccm-manager switchover immediate/graceful/scheduled’ is already not configured.

happy labbing! 🙂


About Mijanur Rahman
Mijanur started blogging to save and share his study and research notes. A deep diver in technologies and loves to participate in technical brainstorming. Proud father of two wonderful daughters loves to spend time with them. He writes about the topics that people deal with every day mainly on technology arena. To get in touch contact him at bilashece@gmail.com

3 Responses to Switchback to Call Agent (CUCM): H.323 and MGCP Approach

  1. What if our wan goes down and the gateway at the remote site goes in SRST mode, the active calls will be preserved or not??

  2. dreamforccie says:

    Thanks! And what about the MGCP call preservation? Is it automatic process or need to configure anything else like H.323?

  3. Roger Kallberg says:

    You might also what to look at configuring call preservation.

    For H.323 call preservation add

    voice service voip

    And: Allow Peer to Preserve H.323 Calls = True in UCM Call Manager advanced service parameters.

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