• Configure T1/E1 interface as in T1/E1 Configuration
• Reduce h225 timeout so it won’t timeout the ISDN when failover btw call manager. The example below reduce the failover time to 3s

voice class h323 1
  h225 timeout tcp establish 3 

• Configure POTS Dial Peer
• With DID, the router/gateway does not present a dial tone to the caller and does not collect digits. It forwards the call directly to the configured destination. This is called one-stage dialing.

dial-peer voice 1 pots
  destination-pattern .T
  incoming called-number .
  direct-inward-dial
  port 0/1/0:15

• Configure VOIP Dial Peer
• Preference: prefer lower preference

dial-peer voice 2 voip
  description Subscriber
  preference 1
  destination-pattern 9235....
  session target ipv4:10.59.228.4	
  voice-class h323 1

• If H.323 gateway has multiple interface, manually specify the source IP address on the interface. The IP address should match what's configured on the interface.

interface GigabitEthernet0/0
 h323-gateway voip bind srcaddr <gw-ip>