8018653 1.1 Introduction • 1-3
1.1
Mobile switching center
The MSC (see figure 1-2) contains an Alcatel 1000 System 12
distributed switching system that interfaces (via E1 trunk circuits) with
one or more base station controllers, providing connections between
them and the public switched telephone network (PSTN).
The MSC processes all requests for calls, controls access to system
features, and performs all switching functions. It controls subscriber
functions of registration, authentication, and records management using
the home location register (HLR) and visitor location register (VLR).
The HLR is a permanent database of all subscribers that is integrated into
a national network of subscriber databases to improve call delivery and
prevent fraud.
The VLR is a semi-permanent, fast-access database that contains sub-
scriber ID, location, and feature information for those users who are, or
recently have been, active in the service area.
Figure 1-2. Alcatel 1000 System 12 distributed switching system (typical)
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