MERLIN LEGEND Communications System Release 5.0
Feature Reference
555-650-110
Issue 1
June 1997
Features
Page 451
Primary Rate Interface (PRI) and T1
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Direct Inward Dial
T1 service provides the following benefits:
■
Speed. Data calls to outside destinations can be made by programming a
channel for T1 Switched 56 Data. This service must be supported on the
far end. By allowing high-speed digital data transmission, T1 provides the
capability for videoconferencing and Group IV (G4) fax.
■
Improved Toll Restriction. The ways in which toll restriction can be
bypassed are limited on T1 lines/trunks. Specifically, three types of toll
abuse are eliminated with T1 service:
— Because dialing is in the form of out-of-band messages that must be
generated by the system, a user cannot use a touch-tone generating
device, such as a pocket dialer, to send dialed digits directly through the
system to the line/trunk.
— Without T1 service, toll restriction can be deceived by dialing digits on a
loop-start line before the far-end switch applies dial tone. These initial
digits may indicate a local call to the system’s toll-restriction checking
while the subsequent digits, those actually recognized by the far-end
switch, may produce a toll call. This is not possible with T1 service
because every digit screened and passed on by the system’s toll
restriction is guaranteed to be received by the far-end switch.
— A T1 line’s far-end disconnect signal provides a reliable indication when
a call ends, and a new call cannot be initiated until the line has been
released from the prior call on both ends. This prevents a user on a
loop-start line, waiting off hook for the restoration of dial tone after a
previous call, from placing a second call before toll restriction is
reapplied.
■
Reliable Indication of Far-End Disconnect. This prevents an incoming
call from being blocked because a line is not released when a call is ended.
T1 supports routing by dial plan on Switched 56 data channels. Routing by dial
plan supports call handling similar to Direct Inward Dial (DID). It performs digit
analysis on incoming calls, matches to Called Party Numbers (CdPNs), and
delivers the calls to the destinations based on the respective Called Party
Numbers. It also allows multiple calls to the same directory number. That is,
multiple concurrent incoming calls with the same Called Party Number can be
delivered to a destination simultaneously.
DS1 Facility Options
3
0
A Digital Signal Level 1 (DS1) facility is a transmission system that transports
digital signals in the DS1 format. The interface that allows the connection of DS1
facilities to the system is the 100D module. Through this module, voice and data
calls can be made or received using a DS1 facility.
Twenty-four Digital Signal Level 0 (DS0) channels, each operating at 64 kbps,
plus framing bits, are multiplexed, forming a DS1 signal of 1.544 Mbps. Each DS0
