AT&T II ユーザーズマニュアル

Your local telephone company provides a block of Centrex lines that are used
with your telephones. When you connect these lines to your equipment
controller and supply electrical power, the controller automatically assigns one
Centrex line to each extension. The only exception is the phone connected to
extension jack 10, which is assigned  all of the lines in your system, to permit a

receptionist to answer calls for users if they do not pick up immediately. (For
more information on call coverage, see “Call Coverage Options” in Chapter 4.)

By default, the primary line for an extension is set for immediate ringing and any
secondary lines are set for delayed ringing. When a call comes in on a line, it
rings immediately at the extension where the line is assigned as a primary line;
after about 20 seconds it also begins to ring at any extensions where the line is
assigned as a secondary line (for example, at the receptionist’s extension).

The equipment controller passes Centrex ringing patterns through to each

phone (for example, Centrex ringing patterns are usually different for outside

and inside calls).

Each Centrex line is identified by a seven-digit telephone number (for example,

555-1212). When someone outside your system calls a Centrex telephone

number (an outside call), the call rings at the extension where that number is
assigned as the primary line.

Users who are on the same Centrex system can generally dial another extension
(an inside call)  using the  Centrex extension number.  The Centrex extension
number is typically the last digits of the telephone number—the number of digits
is determined by the local telephone company, but in most cases the last four or

five digits of the telephone number are used. For example, the Centrex
extension number for 555-1212 might be 1212 or 51212. (Some Centrex
systems may also provide a one-or two-digit “Centrex extension ID” that can be

used to dial other extensions.)

Although users will identify extensions by the Centrex extension number, the
equipment controller tracks lines and extensions using two other numbers,

based on the physical connections at the equipment controller. When your
premises equipment was installed (see Chapter 2), the following connections

were made:

■

Each Centrex line comes into your building from your local telephone
company and terminates at a network interface jack; each network

interface jack is then connected to a line jack on the equipment controller.
Each line jack on the controller is identified by a line jack number. Line

jack numbers run from 01 through 24 (if you have the maximum number
of lines that can be used with your premises equipment).

Using the Equipment