SIP session timers
One of the main issues with SIP is to make sure that the call and dialog finishes properly. However, in the SIP protocol, there is no guarantee that either the UAC or UAS will send the BYE request to terminate the call. Network and device issues can lead to unfinished calls. These calls, also called hanged calls, will stay in the dialog table until its default timeout, by default, 43,200 seconds or, in other words, 12 hours. This time is changeable in the default_timeout parameter.
The Internet Engineering Task Force (IETF) defined a mechanism to detect hanged calls and lack of communication with a specific device. It is now a standard described in RFC 4028. The SIP session timers send periodic messages that continuously update ...
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