Instruction manual

Features
PRI Benefits
The following benefits are provided by PRI service:
■ Speed: Data calls to outside destinations can be established on the
same B-channels used for voice calls if the service allows. Modems and
dedicated, conditioned lines/trunks are not needed.
■ AT&T’s INFO2 station identification/automatic number identification
(SID/ANI) service: number identification service Customers who
subscribe to this service can identify the caller on an incoming call on a
PRI line/trunk by either telephone number or billing number.
NOTE:
The availability of the caller identification information may be limited by
local-serving (caller’s) jurisdiction, availability, or telephone company.
■ Dynamic B-channel assignment: An individual B-channel can be
removed from service without blocking calls to or from any other B-
channels.
■ 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:
— Since 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 bypass a loop-
start or ground-start trunk and send dialed digits in-band directly
through the system to the trunk.
— Without PRI service, toll restriction can be deceived by dialing
digits on a loop-start trunk 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 trunk, 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 trunk has not been released when a
call is over due to a falsely reported far-end disconnect signal or an
electronic disturbance that simulates the signal.
Additionally, by supporting high-speed digital data transmission, PRI provides
the capability for video conferencing and Group IV (G4) Fax.
Primary Rate Interface (PRI)
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