Incoming Calls on Ribbon SBC/Teams Direct Routing fails with 400 Bad Request

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Issue: Incoming Calls on Teams Direct Routing fails with 400 Bad Request

Error: Q.850; Cause=95=”some Uri; Invalid Contact Header: Parsing problem (No viable alternative)

Ribbon SBC 1000, Firmware 8.0.2v520

Invite to Teams:

After 100 Trying, Teams Trunk rejects the call with 400 Bad Request:

Why Teams Gateway rejecting this call?

If you carefully check the INVITE, there are duplicate port in the contact header causing this rejection:

How to fix it? The quick solution would be contact header connection in the Teams SIP Profile.

The snip bellow I have taken when it was not working:

In the above given snapshot, port 5061 was defined after sbc fqdn as static record which is causing this issue.


Make sure the sbc fqdn is correct if you are using static FQDN:



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