Source note · SIP 503 and trunk out-of-service failures
In SIP, 503 Service Unavailable means the server is temporarily unable to process the request because of temporary overloading or maintenance of the server.
Checked 2026-09-25
The server is temporarily unable to process the request due to a temporary overloading or maintenance of the server.
- Vendor
- IETF
- Product
- SIP
- Subsystem
- response codes
- Deployment
- any
- Region
- not restricted
- Release range
- RFC 3261 as quoted in RFC 5390; current as of 2026-09-25
- Checked
- 2026-09-25
Sources
- RFC 5390: Requirements for Management of Overload in the Session Initiation Protocol — IETF / RFC Editor · tier 1 standards and regulators · Section 4 (quotation of RFC 3261 section 21.5.4)
Cite this note
APA
WarmTransfer. (2026, September 25). SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-503-definition. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-503-definition
BibTeX
@misc{warmtransfer-claim-sip-503-trunk-failures-503-definition,
title = {SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-503-definition},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-503-definition},
note = {Source note sip-503-trunk-failures-503-definition, checked 2026-09-25}
}