Overview

SIP timers define the transaction expiration timers, retransmission intervals when UDP is used as a transport, and the lifetime of dynamic TCP connections. The retransmission and expiration timers correspond to the timers defined in RFC 3261.

• init timer: is the initial request retransmission interval. It corresponds to Timer T1 in RFC 3261.

  This timer is used when sending requests over UDP. If the response is not received within this interval, the request is retransmitted. The retransmission interval is doubled after each retransmission.

• max timer: is the maximum retransmission interval for non-INVITE requests. It corresponds to Timer T2 in RFC 3261.

  The retransmission interval is doubled after each retransmission. If the resulting retransmission interval exceeds the max timer, it is set to the max timer value.

• trans expire: is the transaction expiration timer. This value is used for timers B, D, F, H and J as defined in RFC 3261.
• invite expire: defines the transaction expiration time for an INVITE transaction after a provisional response has been received. This corresponds to timer C in RFC 3261.

  If a final response is not received within this time, the INVITE is cancelled. In accordance with RFC 3261, the timer is reset to the invite expire value when any additional provisional responses are received.

• Inactive dynamic conn timer defines the idle time of a dynamic TCP connection before the connection is torn down. Idle is defined as not transporting any traffic. There is no timer in RFC 3261 corresponding to this function.