Source note · SIP 503 and trunk out-of-service failures
A Direct Routing outbound call that draws a 503 from the SBC after the SBC has already sent 180 or 183 will not fail over to another SBC even though 503 is a default failover code.
inferred · Checked 2026-09-25
- Vendor
- Microsoft
- Product
- Teams Phone Direct Routing
- Subsystem
- outbound trunk failover
- Deployment
- multi-tenant
- Region
- not restricted
- Release range
- current as of 2026-09-25
- Status
- inferred
- Checked
- 2026-09-25
Sources
- Trunk failover on outbound calls - Microsoft Teams — Microsoft · tier 2 current vendor documentation · Section 'Failover of specific SIP codes received from the Session Border Controller (SBC)'
Cite this note
APA
WarmTransfer. (2026, September 25). SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-inf-503-after-ringing. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-inf-503-after-ringing
BibTeX
@misc{warmtransfer-claim-sip-503-trunk-failures-inf-503-after-ringing,
title = {SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-inf-503-after-ringing},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-inf-503-after-ringing},
note = {Source note sip-503-trunk-failures-inf-503-after-ringing, checked 2026-09-25}
}