Forum Discussion
MS Teams Direct Routing - Internal call transfer failure
It's both. If your SBC can't handle REFERs - it's a workaround. If it can - you still can prohibit REFERs and use INVITEs as per SIP RFC.
Here's an official explanation:
https://docs.microsoft.com/en-us/microsoftteams/direct-routing-protocols-sip
Section 'Call Transfer':
Call transfer
Direct Routing supports two methods for call transfer:
Option 1. SIP proxy processes Refer from the client locally and acts as a Referee as described in section 7.1 of RFC 3892.
With this option, the SIP proxy terminates the transfer and adds a new Invite.
Option 2. SIP proxy sends the Refer to the SBC and acts as a Transferor as describing in Section 6 of RFC 5589.
With this option, the SIP proxy sends a Refer to the SBC and expects the SBC to handle the Transfer fully.
The SIP proxy selects the method based on the capabilities reported by the SBC. If the SBC indicates that it supports the method “Refer”, the SIP proxy will use Option 2 for call transfers.
Lt_Flash Suddenly having this issue one of remote sbc. We have proxy-remote sbc configuration. All other remote SBC can handle internal call transfer but only one fails. All remote SBCs have same configs. So not sure why it is failing for only one SBC. It has the same unable to purse RURI message from Teams.
- As I wrote a little while ago - we have figured out how to use REFER from MS Teams so currently we're using that method instead of prohibiting it on 'Allow:' level. Works fine witout any issues.
- We're using MS supported Oracle AP3900 SBCs with recent firmware, I would be surprised if REFER is not supported. I think we have more digging to do.
