AT&T MERLIN LEGEND Release 4.0 Feature Reference page 418

Feature Reference
To connect the 100D module to an outside DS1 facility, a channel service unit
(CSU) is used. The CSU regulates the transmission into and out of the 100D
module so that the module matches the transmission of the outside facility.
Both ends of the DS1 facility must be able to communicate. To ensure this, the
following options are set during system programming to match the transmission
of the outside DS1 facility:
Type of service (T1 or PRI)
Framing format
Line coding
Channel service unit
Line compensation
Clock synchronization
Signaling mode (for T1 service only)
NOTE:
Most of these settings are dependent upon the central office and the type of
service (T1 or PRI) you subscribe to.
Type of Service
The system supports two types of service for DS1 facilities: T1 and PRI. The
100D module can be programmed to operate in either type of service. T1
service transmits and receives voice and analog data, as well as digital data in
Release 4.0 communications systems; PRI transmits and receives voice, analog,
and digital data. Any combination of the following AT&T Switched Network
(ASN) Services can be provided through a T1 or a PRI line/trunk:
Megacom WATS service for domestic outgoing long-distance voice calls
Megacom 800 service for domestic toll-free incoming voice calls
Software-Defined Network (SDN) for voice and circuit-switched data calls
MultiQuest for 900 service numbers
PRI interacts with the ACCUNET Switched Digital Service for 56-kbps, 64-kbps
restricted, and 64-kbps clear circuit-switched data calls. T1 supports ACCUNET
Switched Digital Service or other circuit-switched data service at 56 kbps in
Release 4.0 and later.
T1 and PRI support Shared Access for Switched Services (SASS), which allows
both Megacom and Megacom 800 services to be offered over the same line.
This eliminates the need to have separate incoming and outgoing trunks when
these services are chosen.
418
Primary Rate Interface (PRI) and T1