The BCC IE is associated with the 'Setup Message' in the Main Message field. This is the layer three message used during call establishment and its function is seen in the signalling sequences used to control a call in various situations. See Tables 1, 2, 3, 4, 5, 6, 7, 8, 9 for different BCC IE configurations.

It has two key functions. These are implemented in a manner defined by the way its information fields are coded. The task of these information fields is to:

(i) select the Bearer Services in the network which are needed to support the application to be implemented after call establishment.

(ii) check destination terminal compatibility and also support connections to destination terminals in different networks.

Various examples of the way the information fields may be coded are shown in Tables 1, 2, 3, 4, 5, 6, 7, 8, 9.

The attributes of the BCC IE are contained in octets 3 and 4 and 5 (as well as octets 6 and 7 for X25 connections) of the IE. (Octet 1 lists the code which designates the BCC IE and octet 2 describes the number of octets to follow with the BCC IE information). The value of the attributes is determined by the application which is to be supported by the ISDN.

Octet 3 of the BCC IE contains information on the 'Information Transfer Capability' attribute and associated values, viz. speech, unrestricted digital information transfer (UDI) or restricted digital transfer (RDI), 3.1 khz audio, 7 khz audio or video.

Octet 4 of the BCC IE contains information about the 'Transfer Mode' attribute and associated values, i.e. circuit or packet mode, and also the 'Information Transfer Rate' attribute and associated values, i.e. 64 kbit/sec, 2x64 kbit/sec, 384 kbit/sec, 1536 kbit/sec or 1920 kbit/sec.

Octet 5 of the BCC IE describes the coding required at layer one for the information transfer capability, i.e. the coding format of B channel information implemented at layer 1. This information may be modified by the network (to allow interworking with another type of network, for example). It may be included with the Setup message at the start of call establishment by the originating terminal.