Source note · SIP 503 and trunk out-of-service failures
For Microsoft 365, Office 365 and GCC, the SBC should be configured with sip.pstnhub.microsoft.com, sip2.pstnhub.microsoft.com and sip3.pstnhub.microsoft.com in that priority order; GCC High and DoD each use a single FQDN.
Checked 2026-09-25
- Vendor
- Microsoft
- Product
- Teams Phone Direct Routing
- Subsystem
- SIP signalling failover
- Deployment
- multi-tenant
- Region
- not restricted
- Release range
- current as of 2026-09-25
- Checked
- 2026-09-25
Sources
- Plan Direct Routing — Microsoft (Microsoft Learn) · tier 2 current vendor documentation · Sections 'SIP signaling: FQDNs', 'SIP signaling: GCC High', 'SIP signaling: DoD'
Cite this note
APA
WarmTransfer. (2026, September 25). SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-dr-fqdn-priority. WarmTransfer. https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-dr-fqdn-priority
BibTeX
@misc{warmtransfer-claim-sip-503-trunk-failures-dr-fqdn-priority,
title = {SIP 503 and trunk out-of-service failures: source note sip-503-trunk-failures-dr-fqdn-priority},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/sip-503-trunk-failures-dr-fqdn-priority},
note = {Source note sip-503-trunk-failures-dr-fqdn-priority, checked 2026-09-25}
}