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SIP timer summary

Request for Comments (RFC) 3261, "SIP: Session Initiation Protocol," specifies various timers that SIP uses.
Table 1 summarizes for each SIP timer the default value, the section of RFC 3261 that describes the timer, and the meaning of the timer.

SIP timers." id="rsip_reftimesumm__table_timers" border=1 > Summary of SIP timers. This table lists a summary of SIP timers.

Timer Default Section Meaning
T1 500 ms 17.1.1.1 Round-trip time (RTT) estimate
T2 4 sec. 17.1.2.2 Maximum retransmission interval for non-INVITE requests and INVITE responses
T4 5 sec. 17.1.2.2 Maximum duration that a message can remain in the network
Timer A initially T1 17.1.1.2 INVITE request retransmission interval, for UDP only
Timer B 64*T1 17.1.1.2 INVITE transaction timeout timer
Timer D > 32 sec. for UDP 17.1.1.2 Wait time for response retransmissions
0 sec. for TCP and SCTP
Timer E initially T1 17.1.2.2 Non-INVITE request retransmission interval, UDP only
Timer F 64*T1 17.1.2.2 Non-INVITE transaction timeout timer
Timer G initially T1 17.2.1 INVITE response retransmission interval
Timer H 64*T1 17.2.1 Wait time for ACK receipt
Timer I T4 for UDP 17.2.1 Wait time for ACK retransmissions
0 sec. for TCP and SCTP
Timer J 64*T1 for UDP 17.2.2 Wait time for retransmissions of non-INVITE requests
0 sec. for TCP and SCTP
Timer K T4 for UDP 17.1.2.2 Wait time for response retransmissions
0 sec. for TCP and SCTP


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