ISDN Bearer Connection Independent Supplementary Services

Overview

Provision for ISDN Bearer Connection Independent Supplementary Services is implemented using the FACILITY message through the ISDN GCR component (0x09) with optional facility information element (IE) contents. All that is required for these services is the ability to transmit and receive FACILITY messages with a dummy call reference IE.

Existing support for FACILITY messages and both normal and global Call Reference IEs are not affected. ISDN FACILITY messages are sent from the host using the PPL Event Request (0x44). The host is notified of the receipt of the incoming ISDN FACILITY message using PPL Event Indication (0x43).

Implementing incoming calls

Implementation of ISDN Bearer Connection Independent feature for incoming calls requires the following configuration:

• Enable the sending of the FACILITY INDICATION message to the host.

• Set PPL Config Byte 3 of the Global Call Reference component (0x09) to 0x01 (Enable) using PPL Configure (0xD7)

Example incoming call flow

The following indicates the call flow for an incoming FACILITY message with dummy call reference:

1. The network sends a FACILITY message with CR = null to the CSP.

2. The CSP sends a PPL Event Indication (FACILITY) to the host.

Important! The Call Reference IE ICB is not sent to the host in the PPL Event Indication message.

Implementing outgoing calls

The Call Reference Information Element is used in the ISDN Formatted IEs ICB in the PPL Event Request message to send a Call Reference value to the CSP. The format of the ISDN Formatted IEs ICB and the Call Reference IE are shown below:

ISDN Formatted IEs
(Subtype 0x10)

Call Reference IE Format
Data[0] IE Type 0x01
Data[1] Length
Data[2+] Data

To request a dummy call reference, enter the following:

Data[0] IE Type 0x01 Call Reference
Data[1] Length - 0x00
Data[2] There is no data

To send a 1-octet Call Reference value, enter the following:

Data[0] IE Type 0x01 Call Reference
Data[1] Length - 0x01
Data[2] Call Reference value

To send a 2-octet Call Reference value, enter the following:

Data[0] IE Type 0x01 Call Reference
Data[1] Length - 0x02
Data[2] Call Reference value octet 1
Data[3] Call Reference value octet 2

Example outgoing call flow

The following indicates the call flow for an outgoing FACILITY message with dummy call reference.

1. The host sends a PPL Event Request (FACILITY message) to the CSP with a Formatted IEs ICB [null CR IE].

2. The CSP sends to the network a FACILITY message with CR = null.