Source note · SIP 503 and trunk out-of-service failures
Because proxies are told not to relay 503 upstream and Teams reports whether a 503 came from Microsoft (540998) or the SBC (560503), the first troubleshooting step for a 503 is to find which hop generated it before blaming the far-end carrier.
inferred · Checked 2026-09-25
- Vendor
- multi-vendor
- Product
- SIP
- Subsystem
- troubleshooting method
- Deployment
- any
- Region
- not restricted
- Release range
- current as of 2026-09-25
- Status
- inferred
- 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 · Synthesis of rfc-5390 section 4 and ms-learn-troubleshoot-dr-sip-503 sections 540998 and 560503
Cite this note
APA
WarmTransfer. (2026, September 25). SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-inf-503-origin-hop. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-inf-503-origin-hop
BibTeX
@misc{warmtransfer-claim-sip-503-trunk-failures-inf-503-origin-hop,
title = {SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-inf-503-origin-hop},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-inf-503-origin-hop},
note = {Source note sip-503-trunk-failures-inf-503-origin-hop, checked 2026-09-25}
}