Source note · SIP 503 and trunk out-of-service failures
Direct Routing Microsoft response code 560503 with SIP 503 means the 503 came from the SBC (maintenance or temporary overload); Microsoft says to check SBC logs, confirm the SBC is licensed for the concurrent sessions, and see whether the failures are tied to one destination country, region or corridor.
Checked 2026-09-25
- Vendor
- Microsoft
- Product
- Teams Phone Direct Routing
- Subsystem
- call failure codes
- Deployment
- multi-tenant
- Region
- not restricted
- Release range
- current as of 2026-09-25
- Checked
- 2026-09-25
Sources
- SIP 503 and Microsoft response codes - Microsoft Teams — Microsoft · tier 2 current vendor documentation · Section '560503 503 Service unavailable. SBC undergoing maintenance or temporarily overloaded'
Cite this note
APA
WarmTransfer. (2026, September 25). SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-dr-560503-sbc. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-dr-560503-sbc
BibTeX
@misc{warmtransfer-claim-sip-503-trunk-failures-dr-560503-sbc,
title = {SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-dr-560503-sbc},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-dr-560503-sbc},
note = {Source note sip-503-trunk-failures-dr-560503-sbc, checked 2026-09-25}
}