Under RFC 3261 a fatal transport error (such as a fatal ICMP error over UDP or a TCP connection failure) is treated by the UAC as a 503 Service Unavailable, not as a 408.
Checked 2026-10-02
- Vendor
- not restricted
- Product
- not restricted
- Subsystem
- SIP transaction layer
- 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 8.1.3.1 Transaction Layer Errors
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-transport-err-as-503. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-408-timeout-troubleshooting-rfc3261-transport-err-as-503
BibTeX
@misc{warmtransfer-claim-sip-408-timeout-troubleshooting-rfc3261-transport-err-as-503,
title = {Troubleshooting SIP 408 Request Timeout and calls that get no response: source note sip-408-timeout-troubleshooting-rfc3261-transport-err-as-503},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-408-timeout-troubleshooting-rfc3261-transport-err-as-503},
note = {Source note sip-408-timeout-troubleshooting-rfc3261-transport-err-as-503, checked 2026-10-02}
}