High Availability between CUCM and H.323 Gateway

This post describes in great details about how to configure redundancy and customize relevant parameters between CUCM and H.323 Gateway. The following content can be divided into 2 sections: Redundancy configuration on CUCM side, dial-peer & timer configuration on H.323 Gateway side.

Redundancy Configuration on CUCM side:
Route Group Config: Add several gateways into Route Group using Top Down or Circular (default) polling method.

Gateway Device Pool Config: associate the H.323 gateway’s Device Pool with CCM Group containing a list of prioritized CUCM servers.
NOTE: Here, the order of CUCM server should correspond to the dial peer priority configuration of h.323 gateway.

Dial Peer & Timer configuration on H.323 gateway:
Dial Peer Configuration:
dial-peer voice 101
   destination-pattern 2….
   session target ipv4: cucm-1 ip address

dial-peer voice 102
   destination-pattern 2….
   session target ipv4: cucm-2 ip address
   Preference 1

H.323 Timer Configuration:
1. Active Call Survivability: Active call will be dropped if the signaling session between h.323 gateway and CUCM is lost until Cisco IOS 12.4(9T), from which call preservation/call survivability is supported. however, this call preservation is disabled by default, manually enabling is required.
The TCP session between CUCM and H.323 GW is monitored using H.225 keepalives.To avoid call dropping caused by connection failure between CUCM and H.323 GW, use below configuration:
voice service voip
   h323
   no h225 timeout keepalive       //This configuration is for IP to TDM trunk

voice service voip
   allow-connection h323 to h323
   voice class h323 101
   call preserve                //This configuration is for IP to IP trunk gateway (CUBE) 
   Reference: CIPT1:  H.323 Gateway Call Survivability
2. Adjusting Timer parameters to speed up the reroute between dial peers
voice class h323 101
   h225 timeout tcp establish xx       //seconds,  2 seconds recommended, time for setting up TCP connection with CUCM IP address before switch to next dial peer.
   h225 timeout setup xx          //seconds,  2 seconds recommended, time to wait for response from CUCM to H.225 SETUP message.

dial-peer voice 103
   voice-class h323 101