14.2.5.6. SIP Session Timer 
The "SIP Session Timer" provides a "keep alive" system for SIP sessions.
If this feature is activated, reINVITE or UPDATE messages are sent periodically
during an established connection. If the partner answers, the session
is extended by a period of time previously arranged between the partners.
If the partner does not answer, the session is released. This verifies
whether the connection is still established.
The marginal values for the duration of the extension can be set in
the WBM of the gateway:
-
WBM -> Configuration -> Voice Gateway -> SIP Parameters
Figure 239. SIP session timer
- The SIP session timer is activated by the Use RFC4028 checkbox.
- Session Expires: Determines the maximum time by which a session can be extended.
- Minimal SE: Determines the minimum time by which a session can be extended.
The actual duration of the extension also depends on the partner's settings
but is within the configured interval. A session is renewed as soon as
half the duration has expired.
IMPORTANT:
Please note that very short intervals lead to
increased message traffic!