Session Inactivity Timeout in ScreenOS Devices Overview
Typically a call ends when one of the clients sends a BYE or CANCEL request. The SIP ALG intercepts the BYE or CANCEL request and removes all media sessions for that call. There could be reasons or problems preventing clients in a call from sending BYE or CANCEL requests, for example, a power failure. In this case, the call might go on indefinitely, consuming resources on the security device. The inactivity-timeout feature helps the security device to monitor the liveliness of the call and terminate it if there is no activity for a specific period of time.
A call can have one or more voice channels. Each voice channel has two sessions (or two media streams), one for RTP and one for RTCP. When managing the sessions, the security device considers the sessions in each voice channel as one group. Settings such as the inactivity timeout apply to a group as opposed to each session.
- Signaling-inactivity timeout— This parameter indicates the maximum length of time (in seconds) a call can remain active without any SIP-signaling traffic. Each time a SIP-signaling message occurs within a call, this timeout resets. The default setting is 43,200 seconds (12 hours).
- Media-inactivity timeout— This parameter indicates the maximum length of time (in seconds) a call can remain active without any media (RTP or RTCP) traffic within a group. Each time an RTP or RTCP packet occurs within a call, this timeout resets. The default setting is 120 seconds.
If either of these timeouts expires, the security device removes all sessions for this call from its table, thus terminating the call.
