Source note · SIP 503 and trunk out-of-service failures
If several missed calls appear for one declined call, the SBC or PSTN provider retry logic is misconfigured, and the SBC must be set to stop retrying on a 603 response.
Checked 2026-09-25
- Vendor
- Microsoft
- Product
- Teams Phone Direct Routing
- Subsystem
- retry behaviour
- Deployment
- multi-tenant
- Region
- not restricted
- Release range
- current as of 2026-09-25
- Checked
- 2026-09-25
Sources
- Teams Phone System Direct Routing: SIP protocol — Microsoft · tier 2 current vendor documentation · Section 'Handling retries (603 response)'
Cite this note
APA
WarmTransfer. (2026, September 25). SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-dr-603-stop-retry. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-dr-603-stop-retry
BibTeX
@misc{warmtransfer-claim-sip-503-trunk-failures-dr-603-stop-retry,
title = {SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-dr-603-stop-retry},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-dr-603-stop-retry},
note = {Source note sip-503-trunk-failures-dr-603-stop-retry, checked 2026-09-25}
}