Trunk failover on outbound calls - Microsoft Teams

Publisher

Microsoft

URL

https://learn.microsoft.com/en-us/microsoftteams/direct-routing-trunk-failover-on-outbound-call

Published

2025-05-06

Updated

unknown

Accessed

2026-09-25

HTTP status

200

License

Microsoft Learn terms of use; no-redistribution; short excerpts and locators only

Source notes citing this source

• The list of SBC response codes that trigger outbound failover is set per gateway with Set-CsOnlinePSTNGateway -FailoverResponseCodes, and any non-2xx final code can be configured. in context
• In Direct Routing, the default SBC final response codes that trigger retry of an outbound call on another SBC in the voice route are 408, 503 and 504. in context
• 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. in context
• If Direct Routing cannot connect to a trunk (connection refused, TLS timeout or other network error), it retries the same trunk from a different Microsoft datacenter, which may be in another geographic region. in context
• 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 in context
• If Direct Routing cannot connect to a trunk, it retries from a different Microsoft datacenter, possibly in another region, so an SBC ACL that omits some Direct Routing datacenter IP addresses can cause connection failures. in context
• By default Direct Routing retries an outbound call on another SBC in the voice routing policy when the first SBC returns 408, 503 or 504; the list is set with the FailoverResponseCodes parameter. in context
• Direct Routing fails over on a configured response code only if the SBC has sent no non-100 provisional response, which avoids double ringing on the telephone network. in context
• A turn-up failover test is only valid if it reproduces the trigger the platform actually acts on: missing OPTIONS for Direct Routing SBC health or CUBE dial-peer busyout, a configured final response code before any 18x for Direct Routing SIP-code failover, and no SIP response within 4 seconds for Twilio origination. inferred in context

Cite this source record

APA

WarmTransfer. (2025, May 6). Trunk failover on outbound calls - Microsoft Teams. WarmTransfer. https://warmtransfer.net/knowledge/sources/ms-learn-dr-trunk-failover-outbound

BibTeX

@misc{warmtransfer-ms-learn-dr-trunk-failover-outbound,
  title  = {Trunk failover on outbound calls - Microsoft Teams},
  author = {{WarmTransfer}},
  year   = {2025},
  url    = {https://warmtransfer.net/knowledge/sources/ms-learn-dr-trunk-failover-outbound},
  note   = {Microsoft, accessed 2026-09-25}
}