Dialogic 6.2 Manual De Usuario

ISDN Call Processing Overview

November 2009

318

This subsection presents an overview of ISDN incoming and 

outgoing call setup and tear down and overlapped dialing. Switched 

56 calls use a similar mechanism. 

A typical incoming ISDN call is illustrated in 

. In this call 

scenario, the Brooktrout module is answering a call. The following 

message exchange is relative to the module:

1. Call arrival is indicated by receipt of a SETUP message from the 

network containing information about the call (calling party and 

called party numbers, etc.).

2. The module generates two messages upon receipt of the SETUP.

Š

CALL PROCEEDING message to the network indicating the 
call is being processed.

Š

L3L4mSETUP_IND message to the host indicating receipt of 
the SETUP message from the network; information about 

the call (calling party and called party numbers, etc.) is 

included in this message if received from the network.

3. If the incoming call is to be accepted, the host optionally sends an 

L4L3mALERTING_REQUEST message to the module.

4. Upon receipt of the L4L3mALERTING_REQUEST message, the 

module sends an ALERTING message to the network.

5. The host then sends an L4L3mCONNECT_REQUEST to the 

module, asking that the call be connected; the host can consider 

the call connected at this point unless an error indication is 

received.

6. Upon receipt of the L4L3mCONNECT_REQUEST message, the 

module sends a CONNECT message to the network.

7. The network immediately responds with a CONNECT 

ACKNOWLEDGE message and the call is connected.

This scenario does not use B-channel negotiation, which would 

require additional message exchanges between the module and host. 

B-channel negotiation is a feature that allows you to specify on 

which B-channel you want an incoming call to be established.