Section 17 of RFC 3261 defines several SIP Timers
17 Transactions
17.1 Client Transaction
17.1.1 INVITE Client Transaction
17.1.1.1 Overview of INVITE Transaction
17.1.1.2 Formal Description
17.1.1.3 Construction of the ACK Request
17.1.2 Non-INVITE Client Transaction
17.1.2.1 Overview of the non-INVITE Transaction
17.1.2.2 Formal Description
17.1.3 Matching Responses to Client Transactions
17.1.4 Handling Transport Errors
17.2 Server Transaction
17.2.1 INVITE Server Transaction
17.2.2 Non-INVITE Server Transaction
17.2.3 Matching Requests to Server Transactions
17.2.4 Handling Transport Errors
This table is a Summary of SIP Timers that are refined in Section 17 of RFC 3261.
Timer | Default value | Section | Meaning |
|---|---|---|---|
T1 | 500 ms | 17.1.1.1 | Round-trip time (RTT) estimate |
T2 | 4 sec | 17.1.1.2 | Maximum retransmission interval for non-INVITE requests and INVITE responses |
T4 | 5 sec | 17.1.1.2 | 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 for INVITE transactions |
Timer D | >32 sec for UDP 0 sec for TCP/TLS | 17.1.1.2 | Wait time for response retransmissions for INVITE transactions |
Timer E | initially T1 | 17.1.1.2 | Non-INVITE request retransmission interval, UDP only |
Timer F | 64*T1 | 17.1.1.2 | 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 0 sec for TCP/TLS | 17.2.1 | Wait time for ACK retransmissions |
Timer J | 64*T1 for UDP 0 sec | 17.2.2 | Wait time for retransmissions of non-INVITE requests |
Timer K | T4 for UDP 0 sec for TCP/TLS | 17.2.2.1 | Wait time for response retransmissions |