sip media · stub
SIP retransmission timers and transaction state
Verified 2026-09-15 · 6 claims · sources tier 1
Also known as T1, Timer H.
Stub. This topic has 6 verified claims and no published article. The claims below are exactly what the corpus holds today.
So far, no summary has been generated for this topic. The claims below are what the corpus currently holds.
See also
Part of
- SIP transactions and dialogs — When a repeat happens where this topic carries what it means
Related to
- SIP response codes — A provisional response stops retransmission
Claims
| # | Claim | Status | Confidence | Verified |
|---|---|---|---|---|
| 1 | RFC 3261 names 8 lettered timers: A and E set a request retransmit interval starting at the round trip estimate B and F set a transaction timeout at 64 times it C sets a proxy timeout above 3 minutes G sets a response retransmit interval H sets the wait for an acknowledgement at 64 times the estimate and D I J and K set wait times for retransmissions to die out. RFC 3261 — SIP: Session Initiation Protocol · RFC 3261 appendix A, the timer table | fact | 0.90 | 2026-09-15 |
| 2 | Timer C is the only transaction timer given as an absolute duration rather than a multiple of the round trip estimate and it is stated as greater than 3 minutes. RFC 3261 — SIP: Session Initiation Protocol · RFC 3261 sections 16.6 and appendix A | fact | 0.90 | 2026-09-15 |
| 3 | Timer G sets the interval at which a server retransmits an INVITE response starting at the round trip estimate and capped by the 4 second maximum. RFC 3261 — SIP: Session Initiation Protocol · RFC 3261 sections 17.2.1 and appendix A | fact | 0.90 | 2026-09-15 |
| 4 | Three constants underlie every SIP transaction timer: a round trip estimate defaulting to 500 milliseconds a maximum retransmit interval of 4 seconds for non-INVITE requests and INVITE responses and a maximum network lifetime of 5 seconds for a message. RFC 3261 — SIP: Session Initiation Protocol · RFC 3261 appendix A, the timer table | fact | 0.90 | 2026-09-15 |
| 5 | Timer H sets the wait for an acknowledgement at 64 times the round trip estimate and its expiry is what ends a server transaction that never received one. RFC 3261 — SIP: Session Initiation Protocol · RFC 3261 sections 17.2.1 and appendix A | fact | 0.90 | 2026-09-15 |
| 6 | Four timers are scoped to an unreliable transport and become 0 on a reliable one: A and E do not retransmit at all and D I J and K wait 0 seconds instead of their unreliable values. RFC 3261 — SIP: Session Initiation Protocol · RFC 3261 appendix A, the timer table | fact | 0.90 | 2026-09-15 |
Sources
tier 1 standards and regulators
RFC 3261 — SIP: Session Initiation Protocol
Cite this page
APA
WarmTransfer. (2026, September 15). SIP retransmission timers and transaction state. WarmTransfer. https://warmtransfer.net/knowledge/sip-retransmission-timers
BibTeX
@misc{warmtransfer-sip-retransmission-timers,
title = {SIP retransmission timers and transaction state},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/sip-retransmission-timers},
note = {Verified 2026-09-15}
}