AT&T MERLIN LEGEND Release 4.0 Feature Reference page 416

Feature Reference
the FTS2000 network prompts the user to enter the code from the
telephone dialpad.
The system allows an restriction code to be entered with the Account
Code Entry feature. This is especially useful for data calls.
Station Identification/Automatic Number Identification (SID/ANI) as
Calling Party Number (Release 2.0 and later). 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 is
called SID/ANI and results in a more PBX-like performance from the
system.
T1
A DS1 facility programmed as a T1 trunk uses 24 channels, sometimes referred
to as DS0 channels, each with a capacity of 64 kbps. Signaling must be in-band
signaling however, which limits the data rate per channel to 56 kbps when the
channels are programmed for Switched 56.
T1 channels can be programmed to emulate the following types of connections:
Loop-Start
Ground-Start
Switched 56 (56 kbps data)
E&M Tie Trunk
Direct Inward Dialing
The following benefits are provided by T1 service:
Speed. Data calls to outside destinations can be made using by
programming a channel for T1 Switched 56 Data. This service must be
supported on the far end. By supporting high-speed digital data
transmission, T1 provides the capability for video conferencing and
Group IV (G4) fax.
Improved Toll Restriction. The ways that toll restriction can be
bypassed are limited on T1 lines/trunks. Specifically, three types of toll
abuse are eliminated with T1 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 send dialed digits directly through
the system to the trunk.
Without T1 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 T1
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Primary Rate Interface (PRI) and T1