Appendix C Transaction Timers

T1 

500 milliseconds 

17.1.1.1 

RTT Estimate 

T2 

4 seconds 

17.1.2.2 

Maximum retransmit interval for non-INVITE requests and INVITE responses

T4 

5 seconds 

17.1.2.2 

Maximum duration that a message remains in the network 

Timer A 

T1 

17.1.1.2 

INVITE request retransmit interval, for UDP only

Timber B 

64*T1 

17.1.1.2 

INVITE transaction timeout timer

Timer C 

> 3 minutes 

16.6 (bullet 11) 

Proxy INVITE transaction timeout

Timer D 

> 32 seconds for UDP, 0 for TCP/SCTP 

17.1.1.2 

Wait time for response retransmits 

Timer E 

T1 

17.1.2.2 

Non-INVITE request retransmit interval, for UDP only

Timer F 

64 * T1 

17.1.2.2 

Non-INVITE transaction timeout timer

Timer G 

T4 for UDP, 0 for TCP/SCTP 

17.2.1 

INVITE response retransmit interval

Timer H 

64 * T1 

17.2.1 

Wait time for ACK receipt

Timer I 

T4 for UDP, 0 for TCP/SCTP 

17.2.1 

Wait time for ACK retransmits

Timer J 

64 * T1 for UDP, 0 for TCP/SCTP 

17.2.2 

Wait time for non-INVITE request retransmits

Timer K 

T4 for UDP, 0 for TCP/SCTP 

17.1.2.2 

Wait time for response retransmits