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Call control procedures
Introduction
A telephone call consists of a signaling component and a voice and data
component. The voice and data component contains the information
transferred between callers. The signaling component contains the
supervisory and address signals that switching offices use to control the
setting up, monitoring, and taking down of the call.
This chapter describes the basic call control procedures used to set up and
take down PRI calls. PRI calls are controlled by a sequence of signaling
messages that flow across the user-network interface. For more information
about the meaning of signaling messages and their role in call processing,
see Chapter 4, "Message structure and functions."
DMS-250 switch functions and services
The DMS-250 switch provides the following functions and services:
Switch network parameter
In any PRI connection, one end functions as the user and the other end as the
network. The IFCLASS parameter in table TRKSGRP specifies whether the
authorization of the call by collection and validation of
— authorization codes (authcodes)—multidigit codes used to identify a
subscriber, to bill a call, and to screen against unauthorized access to
the MWC network
— personal identification number (PIN) digits—a unique number along
with an access code used to activate a service
— supplementary codes or account codes (optional)—multidigit codes
that allow charge back of calls to projects, departments, or accounts
translation and call screening
user tones and announcements
routing of calls to their destination
call detail records for billing purposes
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
5-1
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