Quick Note on H323 and MGCP call preservation

A quick summary on H323 and MGCP gateway call preservation behavior when it works with UCM:

MGCP (primary UCM dies)

PSTN <-- MGCP GW --> UCM <--> Phone

- enabled by default

- UCM dies, call preserved

- Call continues over the gateway

- supplementary services will not work

- new calls to MGCP gateway will not work until MGCP gateway re-registers with the backup UCM

H323 (primary UCM dies)

PSTN <-- H323 GW --> UCM <--> Phone

- Default has no call preservation

- configure with "call preserve" command

- will immediately begin to use backup UCM for supplementary service, outbound and inbound call routing

Branch voice gateway (WAN link down)

- SRST kicks in

- If MGCP, then MGCP fallback - fallback to H323 / SIP processing

- MGCP - Call drop immediately at the branch router

- H323 is recommended for branch router - call preservation feature after IOS 12.4(9T)

Call preservation is configured in the gateway with the following command syntax:

Router(config)#voice service voip
Router(conf-voi-serv)#h323
Router(conf-serv-h323)#call preserve

MGCP fallback is configured with the following command syntax:

Router(config)#ccm-manager fallback-mgcp
Router(config)#application
Router(config-app)#global

Router(config-app-global)#service alternate Default