--- title: "Call Transfer: SIP REFER and Pro Transfer" slug: "call-transfer-using-sip-refer" updated: 2026-05-28T02:17:25Z published: 2026-05-28T02:17:25Z canonical: "kb.connecttoteams.com/call-transfer-using-sip-refer" --- > ## Documentation Index > Fetch the complete documentation index at: https://kb.connecttoteams.com/llms.txt > Use this file to discover all available pages before exploring further. # Call Transfer: SIP REFER and Pro Transfer ## **Call Transfer: Using SIP REFER** Microsoft Teams does not naturally send a REFER message to your PBX when a call is transferred or parked. This causes broken SIP flows or incomplete information for normal processing. ![](https://cdn.us.document360.io/312e5ae5-e3c1-465d-8e37-f253a7ba8eee/Images/Documentation/image-SQP19Y0M.png) To use REFER, you must opt in to that functionality on each direct route. Navigate to the Enterprise's Dashboard page, and in the **Direct Routing Connection Status** table, locate the row for the desired domain. In the **Forward REFER to PBX** column, click **Active**. The indicator will change from red (Inactive) to green (Active), confirming that the REFER is now enabled for that Direct Route. #### **Benefits of enabling REFER:** - Call parking and transferring will work as is typical. #### **Drawbacks of enabling REFER:** - Attended transfers will not work unless the PBX hairpins the transferred call back to Teams where the media is anchored. - The only supported codec is G.711 - In Netsapiens versions earlier than v43.2, there is a known compatibility issue with Netsapiens and Microsoft with transfers. Netsapiens does not send a NOTIFY to let Microsoft know the status of the transfer; it sends a BYE instead. The Netsapiens workaround is to NOT enable REFER in the ConnecttoTeams portal; this lets ConnecttoTeams' SBC handle processing of the REFER instead of asking the PBX to handle it (incorrectly). ## Pro Transfer **Pro Transfer** is an enhanced transfer option that allows the Direct Routing PBX Teams user to transfer calls in several ways: - **Transfer BY NAME** to another Teams user (whether or not that user is configured with a Direct Routing number or extension) - Transfer by PBX extension number - Transfer to PSTN number via the PBX Enabling the Pro Transfer requires some changes in both the Direct Routing setup and also on the PBX, as described below. #### On the ConnecttoTeams Side 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. > [!NOTE] > Note > > 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. To enable Pro Transfer for a Direct Route, navigate to the Enterprise's Dashboard page. In the **Direct Routing Connection Status** table, locate the row for the desired domain, and in the **Pro Transfer** column, click **Active**. The indicator will change from red (Inactive) to green (Active), confirming that Pro Transfer is now enabled for that Direct Route. ![](https://cdn.us.document360.io/312e5ae5-e3c1-465d-8e37-f253a7ba8eee/Images/Documentation/image-345XPF1X.png) #### 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 by-name who is NOT a DR user. We are able to “fix” transfers by-name to other Teams DR users so that they can be handled like any other transfer. 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` . For example: ```plaintext Refer-To: ``` There is also a `x-refer-id` param which would be helpful to include on the resulting `INVITE`, but isn’t strictly necessary. **Routing rules on the PBX** must be configured to recognize this 0770 prefix and process the call as described below. The resulting `INVITE` should be created in the typical way but routed to `edge.connecttoteams.com`: ```plaintext INVITE sip:0770xxxxxxxxxxx@edge.connecttoteams.com SIP/2.0 Via: SIP/2.0/UDP 37.27.0.198:5060;branch=z9hG4bK75a620bf Max-Forwards: 70 From: ;tag=as51cbf31a To: ``` When we get that `INVITE` with the 0770 prefix we are able to reconstruct the necessary headers and send the `INVITE` to Teams to complete the transfer. #### Example Configuration for Asterisk These are example changes for Pro Transfer for an Asterisk PBX. In `extensions.conf` (Dialplan): ```plaintext exten => _0770X.,1,Dial(PJSIP/${EXTEN}@edge.connecttoteams.com) ``` In `pjsip.conf`: ```plaintext [edge.connecttoteams.com] type=endpoint aors=edge.connecttoteams.com disallow=all allow=ulaw [edge.connecttoteams.com] type=aor contact=sip:edge.connecttoteams.com:5060 ```