Consultation Call Transfer

The device supports Consultation Call Transfer. For analog interfaces: It supports Consultation Call Transfer using the SIP REFER message and the Replaces header.

The common method to perform consultation transfer is described in the following example, which assumes three call parties:

■ A = transferring party
■ B = transferred party
■ C = transferred to party
1. A Calls B.
2. B answers.
3. A presses the hook-flash button and places B on-hold (party B hears a hold tone).
4. A dials C.
5. After A completes dialing C, A on-hooks the phone to transfer the call so that the call is established between B and C.

The transfer can be initiated at any of the following stages of the call between A and C:

■ Immediately after A completes dialing C (transfer at call setup)
■ While A hears a ringback (transfer from alert)
■ While A speaks to C (transfer from active)

For FXS interfaces: The device can also handle call transfers using SIP INVITE and re-INVITE messages, instead of REFER messages. This is useful when communicating with SIP UAs that do not support the receipt of REFER messages. This feature is applicable to FXS interfaces. To enable this support, use the EnableCallTransferUsingReinvites parameter.

For BRI interfaces: The device also supports attended (consultation) call transfer for BRI phones (user side) connected to the device and using the Euro ISDN protocol. BRI call transfer is according to ETSI TS 183 036, Section G.2 (Explicit Communication Transfer – ECT). Call transfer is enabled using the EnableTransfer and EnableHoldtoISDN parameters.

➢ To configure call transfer for connected BRI phones:
1. Open the Supplementary Services Settings page (Setup menu > Signaling & Media tab > Gateway folder > DTMF & Supplementary > Supplementary Services Settings).
2. From the 'Enable Hold to ISDN' drop-down list (EnableHoldtoISDN), select Enable.
3. From the 'Enable Transfer' drop-down list (EnableTransfer), select Enable.
4. Click Apply.

The Explicit Call Transfer (ECT, according to ETS-300-367, 368, 369) supplementary service is supported for BRI and PRI trunks. This service provides the served user who has two calls to ask the network to connect these two calls together and release its connection to both parties. The two calls can be incoming or outgoing calls. This service is similar to NI-2 Two B-Channel Transfer (TBCT) Supplementary Service. The main difference is that in ECT one of the calls must be in HELD state. The ECT standard defines two methods - Implicit and Explicit. In implicit method, the two calls must be on the same trunk. BRI uses the implicit mechanism. PRI uses the explicit mechanism.