Dialogic 6.2 manual Isdn Call Processing Overview, Making an Isdn Incoming Call, November 318

ISDN Call Processing Overview

ISDN Call Processing Overview

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.

Making an ISDN Incoming Call

A typical incoming ISDN call is illustrated in Figure 48. 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.

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

ŠL3L4mSETUP_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.

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