Verilink AS56/56Plus (896-502588-001) Product Manual - Manual (Page 15)

T1 Concepts
AS56 and AS56 Plus User Manual 1-3
T1 Concepts
A T1 digital transmission facility carries twenty-four 64 Kbps DS0
“channels,” for a total of 1.536 Mbps (plus 8K bps overhead to achieve
the well-known 1.544 Mbps). These DS-0s can be demultiplexed by
equipment such as Verilink’s Access Sys tem56 units, and groups of DS0s
can be assigned to specific connectors on the equipment to transport
computer information. In some cases, the user has access to the full 64
kbps per channel while, in other cases, the user is limited to 56 kbps per
channel. A detailed explanation is provided in Chapter 3, Configuring and
Installing the Access Syst em56.
The T1 facility itself can be a physical point-to-point circuit with all
twenty-four DS0s going from one site to another. The facility can also be
“Integrated Access,” that uses a Central Office DACS and one or more
Fractional-T1 (F-T1) links. This is a physical multipoint facility with
logical point-to-point links formed by groups of DS0s.
NMS (SNMP) Configuration, on page 6-29, describes examples of Access
System 56 usage with both point-to-point and Integrated Access,
Fractional T1 facilities.
Special Access
Syste m56 Features Built-In 56/64 kbps DDS CSU
Interfacing to 56/64 kbps digital data system (DDS) service requires a
DDS CSU (Channel Service Unit). The Access Syst em56 includes a
built-in 56/64 kbps DDS CSU as standard equipment.
Built-In T1 ESF CSU
Interfacing to T1 or Fractional T1 services requires a T1 CSU. The
Access Syst em56
Plus
includes a built-in T1 ESF CSU as standard
equipment. The superior ESF (Extended SuperFrame) CSU includes
provisions for continuous performance monitoring by both the user and
the telephone company central office. ESF provides a 4 Kbps link control
channel (transparent to user data) which allows the telephone company to
monitor the local loop, transmit and receive test messages and retrieve
performance data, all without interrupting normal operations.