Under the documented in-service rule, a far end that answers OPTIONS with an error other than 408 or 503 (for example 404 or 405) would still keep the destination in service.
inferred · Checked 2026-10-02
- Vendor
- Cisco
- Product
- Unified Communications Manager
- Subsystem
- SIP OPTIONS ping
- Deployment
- on-premises
- Region
- not restricted
- Release range
- 8.5(1) design guidance; later releases not verified
- Status
- inferred
- Checked
- 2026-10-02
Sources
- Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide, Release 8.5(1)) — Cisco Systems · tier 2 current vendor documentation · SIP OPTIONS Ping
Cite this note
APA
WarmTransfer. (2026, October 2). Troubleshooting Unified CM SIP trunks that show No Service: source note cucm-sip-trunk-no-service-troubleshooting-non-503-4xx-up. WarmTransfer. https://warmtransfer.net/knowledge/claims/cucm-sip-trunk-no-service-troubleshooting-non-503-4xx-up
BibTeX
@misc{warmtransfer-claim-cucm-sip-trunk-no-service-troubleshooting-non-503-4xx-up,
title = {Troubleshooting Unified CM SIP trunks that show No Service: source note cucm-sip-trunk-no-service-troubleshooting-non-503-4xx-up},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/cucm-sip-trunk-no-service-troubleshooting-non-503-4xx-up},
note = {Source note cucm-sip-trunk-no-service-troubleshooting-non-503-4xx-up, checked 2026-10-02}
}