MERLIN LEGEND Communications System Release 6.1
Feature Reference
555-661-110
Issue 1
August 1998
Features
Page 498Primary Rate Interface (PRI) and T1
â– Speed. Data calls to outside destinations can be established on the same
B-channels used for voice calls if the service allows. Dedicated,
conditioned lines/trunks are not needed. By supporting high-speed digital
data transmission, PRI provides the capability for videoconferencing and
Group IV (G4) fax.
â– Dynamic B-Channel Assignment. An individual B-channel can be
removed from service without blocking ISDN calls to or from any extension.
â– Improved Toll Restriction. The ways that toll restriction can be bypassed
are limited on PRI lines/trunks. Specifically, three types of toll abuse are
eliminated with PRI 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 PRI 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 PRI 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 PRI 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.
â– 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.
The system’s implementation of PRI provides the following features:
■Support for Caller Identification. The system supports AT&T’s INFO2
Station Identification/Automatic Number Identification (SID-ANI) Service
and, in Release 4.2 and later systems, similar services from MCI and local
exchange carriers. Customers who subscribe to one of these services can
identify the incoming caller on a PRI line/trunk by either telephone number
or billing number. The Calling Party Number (CPN) in Release 1.0 is
facility-based, whereas it can be extension-based in Release 2.0 and later,
if so programmed. Extension-based CPN results in a more PBX-like
performance from the system.
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