Background
With most Teams telephony solutions, transferred calls present a dilemma. When a Teams user transfers an external call to another Teams user, the external telephony platform is not aware that the call has been transferred and the transferor’s call status remains busy for the duration of the transferred call. ConnecttoTeams solves this problem by syncing the Teams transfer status with the external telephony platform so that the transferor becomes available as soon as the call is transferred. This means that call queues and ring groups can wok optimally to route inbound calls to the intended recipient unhampered by the unreliable transfer handling exhibited by many Teams telephony integrations. Importantly, the ConnecttoTeams Pro Transfer solution works even in cases where the transferee is not a phone system licensed user.
Pro-Transfer, also referred to as Enhanced Transfer or B-Profile Transfer, is a feature that enables advanced call transfer capabilities, especially useful for Microsoft Teams integrations and advanced call handling scenarios.
Key aspects of Pro-Transfer include:
Functionality : It allows for enhanced consultative call transfers within Microsoft Teams. When enabled, it ensures that all transfers, including those initiated by searching a user's name, are routed through the Private Branch Exchange (PBX), allowing for proper voicemail handling if a call is unanswered.
Configuration : Enabling Pro-Transfer typically involves updating the relevant voice trunk or Session Border Controller (SBC) domain to a "B profile". This is a backend feature that needs to be enabled by support for each tenant and may require specific call handling on your PBX to recognize Pro-Transfer calls.
Benefits : It resolves issues where transfers to internal Teams users do not complete as expected or where the original caller's line remains engaged after a transfer. It also ensures that unanswered calls are properly routed to PBX voicemail.
Implementation : The process often involves a DNS change to cause the Direct Route domain to resolve to a different profile on the SBC. It is recommended to first create a separate Direct Route for testing before applying the change to the main direct route domain.
Requirements
On the ConnecttoTeams Side
Pro Transfer must be enabled per tenant by a Support request. We make a DNS change to cause the Direct Route domain to resolve to a different profile on the SBC that is configured to deal with the Pro Transfer calls.
Since this will impact ALL transfers made on that Direct Route, we suggest first creating a separate Direct Route on your internal Enterprise for testing your PBX handling of the Pro Transfer scenario. A couple of test users can be assigned to that direct route to test the various transfer scenarios. Once that works, then we can make the change to your main direct route domain.
On the PBX
The only difference in call handling on the PBX will involve transfers by a Teams Direct Routing user to another Teams user who is NOT a Direct Routing user. In the case of a transfer to a non-DR user, we will construct a Refer-To header with a special prefix 0770 and a special domain edge.connecttoteams.com
Refer-To: <sip:[email protected];x-refer-id=fa7016f8-d4a1-11ef-aa21-0022482b9ee7>
There is also a x-refer-id param which would be helpful to include on the resulting INVITE, but isn’t strictly necessary.
When the PBX receives this REFER message, it must route the resulting INVITE to edge.connecttoteams.com (maintaining the prefix of 0770):
INVITE sip:[email protected] SIP/2.0
Via: SIP/2.0/UDP 19.27.0.198:5060;branch=z9hG4bK75a620bf
Max-Forwards: 70
From: <sip:[email protected]>;tag=as51cbf31a
To: <sip:[email protected]>
When we receive that INVITE with the 0770 prefix we are able to reconstruct the necessary headers and send the INVITE to Teams to complete the transfer.