Source note · SIP 503 and trunk out-of-service failures
Direct Routing fails an outbound call over to another SBC only if the first SBC has sent no non-100 provisional response, to avoid double ringing.
Checked 2026-09-25
Note that failover will only happen in the absence of non-100 provisional responses from the SBC, to prevent double ringing telephony network.
- 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
- 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)', first paragraph
Cite this note
APA
WarmTransfer. (2026, September 25). SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-dr-failover-no-provisional. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-dr-failover-no-provisional
BibTeX
@misc{warmtransfer-claim-sip-503-trunk-failures-dr-failover-no-provisional,
title = {SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-dr-failover-no-provisional},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-dr-failover-no-provisional},
note = {Source note sip-503-trunk-failures-dr-failover-no-provisional, checked 2026-09-25}
}