For an INVITE client transaction over an unreliable transport, Timer A starts at T1 and the retransmission interval doubles each time Timer A fires.
Checked 2026-10-02
- Vendor
- not restricted
- Product
- not restricted
- Subsystem
- SIP INVITE client transaction
- Deployment
- any
- Region
- not restricted
- Release range
- RFC 3261, current as of 2026-10-02
- Checked
- 2026-10-02
Sources
- RFC 3261 — SIP: Session Initiation Protocol — IETF / RFC Editor · tier 1 standards and regulators · Section 17.1.1.2 Formal Description
Cite this note
APA
WarmTransfer. (2026, October 2). Troubleshooting SIP 408 Request Timeout and calls that get no response: source note sip-408-timeout-troubleshooting-rfc3261-timer-a-doubling. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-408-timeout-troubleshooting-rfc3261-timer-a-doubling
BibTeX
@misc{warmtransfer-claim-sip-408-timeout-troubleshooting-rfc3261-timer-a-doubling,
title = {Troubleshooting SIP 408 Request Timeout and calls that get no response: source note sip-408-timeout-troubleshooting-rfc3261-timer-a-doubling},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-408-timeout-troubleshooting-rfc3261-timer-a-doubling},
note = {Source note sip-408-timeout-troubleshooting-rfc3261-timer-a-doubling, checked 2026-10-02}
}