# Two B-Channel Transfer

## Description

Two B-Channel Transfer (TBCT; also known as Release Line Transfer) allows a MiVoice Business set user to transfer an external call to another external destination and have the two external parties connected through the trunks at the Central Office (CO) or SIP service provider. Because the calls are connected at the CO or SIP service provider instead of MiVoice Business, the incoming and outgoing trunks on MiVoice Business that would normally be required to connect the external parties are available for use.

TBCT is supported for Bellcore and 5ESS variants of the NI-2 protocol for the embedded ISDN offerings of MiVoice Business, as well as for SIP solutions.

NOTE: SIP TBCT is not supported for EHDUs.

The following figure illustrates a TBCT for ISDN.

TBCT for ISDN

## SMDR Recording

MiVoice Business supports the tagging of TBCT calls by the CO or SIP Service Provider. You can enable SMDR to record these tags and then use the tags to track the costs of TBCT calls.

### ISDN Model

When the user initiates the transfer and the system releases the trunks, the CO sends MiVoice Business a unique tag. SMDR appends this tag to the call record of the incoming trunk call. After the external call clears down, the CO then sends the same tag again to the system. SMDR then generates another record with this tag to identify when the external call cleared down. See SMDR Examples.

NOTE: Calls are charged as if the transfer had not taken place.

If the two ISDN trunks are located on the same system, the SMDR records for both of the ISDN trunks will contain the tag. In the case of a network transfer, the ISDN trunks are located on different systems and the systems are connected via DPNSS or IP trunks. In this case, the tag is written into the SMDR records of both trunks (ISDN and DPNSS or IP trunk) on the system that hosts the ISDN trunk that was on hold at the time that the transfer was initiated.

### SIP TBCT

SIP supports the initial SMDR recording, but it does not support sending a message from the service provider when the TBCT call ends, so there is no SMDR recording for SIP TBCT call termination. Service provider's billing records must be used to determine the true length of the call.

NOTE: SIP sends a REFER message to perform SIP TBCT.

## Conditions and Feature Interactions

- You must purchase support for TBCT from the CO.

- TBCT must be enabled at the CO. If the feature is not enabled, a TBCT request from MiVoice Business is ignored and the trunks are connected together through MiVoice Business.

- TBCT only works on trunks that are in the same Central Office PRI group. It does not work between Central Offices.

- TBCT functions on a local MiVoice Business system or across a private MSDN/DPNSS network.

- Currently, the maximum number of active transfers supported by the CO is 127. If the maximum number of active transfers is already in use, a TBCT request from MiVoice Business is ignored and the trunks are connected together through MiVoice Business.

- Interconnect, Tenanting, and COS restrictions that currently prevent CO trunk calls from being transferred together also prevent TBCT calls.

- For SIP networks, TBCT can be initiated when at least one of the two external calls is answered and the other call:

- if outgoing, may be either answered or alerting

- if incoming, must be answered.

- SIP TBCT is only allowed to the same service provider from the same MiVoice Business.

## Programming

1. Class of Service Options form

- Enable "Two B-Channel Transfer Allowed" in the COS of the device (attendant console or set).

2. SMDR Options form

To enable SMDR recording of TBCT calls, set the following options to "Yes":

- SMDR Extended Reporting Level 2

- Two B-Channel Transfer Recording

If TBCT is being performed in a network, also set the following options to "Yes":

- Standardized Call ID Format

- Standardized Network OLI

## Device Support

A user can initiate a TBCT from any device that can transfer a trunk call or form a trunk-to-trunk conference.

## Operation

See Transfer