Transferring an In-Progress Call to a CommPeak DID

CommPeak supports the Session Initiation Protocol SIP REFER method across all of its global Points of Presence (PoPs). This article walks you through transferring an established call to one of your CommPeak Direct Inward Dialing (DID) numbers from your Private Branch Exchange (PBX) or a third-party AI agent, handing off call routing directly to the CommPeak network.

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IMPORTANT
To use SIP REFER transfers, you need at least one Active CommPeak DID provisioned on your account. To order one, see the Ordering DID Numbers page.

How the transfer works

When CommPeak receives a valid in-dialog REFER request, it validates the transfer and performs a blind transfer:

CommPeak's originates a new call to the configured destination of the target DID.
The remaining party on your call is bridged to the new call. Media stays anchored on CommPeak, so your side does not need to renegotiate media.
CommPeak sends NOTIFY messages back to you, reporting the transfer progress: 100 Trying, 200 OK, and the final status.

CommPeak presents the transferring party's identity as the From header of the new call.

Sending the REFER request

Send the REFER request within the existing dialog (same Call-ID and tags), with the Refer-To header pointing at the target DID on did.commpeak.com:

REFER sip:… SIP/2.0
…
Refer-To: <sip:<DID>@did.commpeak.com>
Referred-By: <sip:[email protected]>; optional

The request must meet all of the following requirements:

<DID> is a numeric DID, with an optional leading + , for example, 447520640056 or +447520640056.
The DID is an Active CommPeak DID that you own.
The host in the Refer-To header is exactly did.commpeak.com.

Target SIP URI for the SIP REFER transfer: sip:[email protected]

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IMPORTANT
The DID shown in the sample above is a placeholder only. Replace it with an Active DID from your own CommPeak account; the transfer fails with 403 Forbidden if you do not own the target DID.

Response codes

After you send the REFER request, CommPeak returns one of the responses described in the table below.

Response	Meaning
`202 Accepted` + `NOTIFY` messages	The transfer is accepted and in progress.
`403 Forbidden`	You do not own the target DID.
`404 Not Found`	The DID is unknown, or the `Refer-To` user part is empty.
`480 Temporarily Unavailable`	The `Refer-To` value is not a valid numeric DID at `did.commpeak.com`.

Enabling SIP REFER on AI agent platforms

Most AI agent platforms do not send SIP REFER by default. Before your agent can transfer calls, you must explicitly enable a dedicated side tool, module, or advanced signaling flag in your AI provider's console.

Open your AI agent provider's console.
Locate the call transfer, SIP REFER, or advanced signaling option; the naming varies by platform.
Enable it, and set did.commpeak.com as the transfer target host where the platform requires one.

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NOTE
If your platform's transfers keep failing even though your SIP configuration is correct, check this setting first - a disabled transfer module is the most common cause.

Transfer limitations

Only in-dialog REFER requests - sent on an active call - are supported. Out-of-dialog REFER requests are rejected.
The Refer-To user part is validated as numeric. Non-numeric targets are rejected.

For DID or transfer configuration requests, submit a ticket to CommPeak support.