Call Transfer; Consultation Call Transfer; Consultation Transfer For Qsig Path Replacement - AudioCodes Mediant 800B User Manual

User's Manual
26.5

Call Transfer

This section describes the device's support for call transfer types.

26.5.1 Consultation Call Transfer

The device supports Consultation Call Transfer using the SIP REFER message and
Replaces header. The common method to perform a consultation transfer is described in
the following example, which assumes three call parties:

Party A = transferring

Party B = transferred

Party C = transferred to
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 can perform the transfer by on-hooking the A phone.
6. After the transfer is complete, B and C parties are engaged in a call.
The transfer can be initiated at any of the following stages of the call between A and C:

Just after completing dialing C phone number - transfer from setup

While hearing ringback – transfer from alert

While speaking to C - transfer from active
Note:
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.
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.
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, and PRI the explicit mechanism.

26.5.2 Consultation Transfer for QSIG Path Replacement

The device can interwork consultation call transfer requests for ISDN QSIG-to-IP calls.
When the device receives a request for a consultation call transfer from the PBX, the
device sends a SIP REFER message with a Replaces header to the SIP UA to transfer it to
Version 7.0
For FXS interfaces, the device can also handle call transfers using SIP
26. Configuring Supplementary Services
535 Mediant 800B Gateway and E- SBC