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Disconnect delay occurs after VoIP call between H.323 gateways connected over ISDN


Core Issue

The network topology is as shown:

R3640D--(BRI)--(ISDN Simulator)--(BRI)--R3640E

A VoIP call is established from an H.323 gateway (R3640E) to another H.323 gateway (R3640D). The user expectation is that once the VoIP call is completed successfully, the connection should be terminated and the ISDN link drops by idle-timer (120 seconds) expiration.

However, the ISDN connection is maintained for 12 minutes. IP packets are seen traversing the ISDN link every minute (like a keepalive).

Note: This behavior is observed only by 12.3 main. It is not observed in 12.2 main.


When a call is established across H.323 gateways, where the gateways are the endpoints of the call, the H.225 session remains active for 10 minutes after the call termination.

This delayed connection termination capability has been added to H.323 gateways. This avoids situations where toggling a single call causes the line to be raised and dropped repeatedly.

For more information, refer to h225 timeout tcp call-idle (H.323 voice-service).

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