The INVITE client transaction state machine as redrawn in RFC 6026 shows that from the Calling state, Timer B firing or a transport error leads to informing the transaction user and terminating.
Checked 2026-10-02
Timer B fires / or Transport Err. / inform TU
- Vendor
- not restricted
- Product
- not restricted
- Subsystem
- SIP INVITE client transaction
- Deployment
- any
- Region
- not restricted
- Release range
- RFC 6026, current as of 2026-10-02
- Checked
- 2026-10-02
Sources
- RFC 6026: Correct Transaction Handling for 2xx Responses to Session Initiation Protocol (SIP) INVITE Requests — IETF / RFC Editor · tier 1 standards and regulators · Section 8.4, updated Figure 5 (INVITE client transaction)
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-rfc6026-timer-b-informs-tu. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-408-timeout-troubleshooting-rfc6026-timer-b-informs-tu
BibTeX
@misc{warmtransfer-claim-sip-408-timeout-troubleshooting-rfc6026-timer-b-informs-tu,
title = {Troubleshooting SIP 408 Request Timeout and calls that get no response: source note sip-408-timeout-troubleshooting-rfc6026-timer-b-informs-tu},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-408-timeout-troubleshooting-rfc6026-timer-b-informs-tu},
note = {Source note sip-408-timeout-troubleshooting-rfc6026-timer-b-informs-tu, checked 2026-10-02}
}