# Supplementary services under NI2

This section provides an overview of the supplementary services available with the NI2 variant and how these services operate in the network architecture. It describes:

- The National ISDN 2 (NI2) variant

- Using supplementary services

- PRI two B channel transfer

- Call identification services

## National ISDN 2 (NI2) variant

NI2 specifications describe a protocol designed to access network services from an intelligent user terminal. The protocol is not symmetric, and requires two distinct roles, the user side and the network side. NMS ISDN supports both sides for basic call control, but NMS ISDN supplementary services only support the user side.

## Using supplementary services

Under NI2, most supplementary services require subscription. Subscription services are optional services provided by the network operator by request. When you request network services from a provider, you can also request one or more subscription services. These services are not available unless the interface is provided with them.

Note: Some supplementary services may not require subscription.

## PRI two B channel transfer

The two B channel transfer (TBCT) service allows an application at the user side to request the transfer of two independent calls. To use the service, the user should be subscribed to TBCT.

The following table lists call transfer operations that can be performed under NI2:

Operation | Description
--- | ---
Invoke two B channel transfer | The application sends a request to the network to transfer two independent calls.
Two B channel transfer notification | The network notifies the application that the call previously transferred by TBCT has been cleared. To receive this notification, the user should be subscribed to the notification to controller feature.

## Call identification services

All of the call identification services for the ETS 300 variant are also implemented for NI2. In addition, the following identification services are implemented in NMS ISDN:

Service | Usage
--- | ---
Calling name identification presentation (CNIP) | The called party receives the name of the calling party. Available only under the NI2 and Q.SIG variants.
Connected name identification presentation (CONP) | The calling party receives the name of the called party. Available only under the NI2 and Q.SIG variants.