ADTRAN TSU LT User Manual download pdf (Page 13)

61202.060L2-1 TSU LT User Manual 1

Chapter 1

Introduction

T1/FT1 OVERVIEW

T1 digital communication links have been used by the telephone companies

(telcos) for voice transmission since the early sixties. The D4 channel bank is

an example of a T1 digital carrier system that was introduced in the mid-sev-

enties and is still widely used by the telcos. Communication demands of busi-

nesses continued to grow to the point that the telcos began offering T1 service

directly to the public. D4 channel banks began to be used for T1 in corporate

network topographies for voice. The technological advances in computer de-

velopment also created a demand for T1 data communication which now is a

large part of the T1 traffic.

T1 Service Offerings

T1 is a digital service that is delivered to the user over two pairs of wires from

the service provider. The signal operates at 1.544 mega bits per second (Mbps)

and is usually extended by repeaters that are installed about every mile after

the first 6000 feet. The T1 signal is divided into 24 time slots or digital signal

level zeros (DS0s) which operate at 64 kilo bits per seconds (kbps). Each time

slot is occupied by digitized voice or by data.

The T1 signal originally used a type of framing known as D4 Superframe

which identifies how the T1 is multiplexed. Extended Superframe (ESF) is an

enhancement of that framing format. ESF provides a non-disruptive means of

full time monitoring on the digital facility. It was originally used by the service

provider to monitor the performance of their service offering. Since the intro-

duction of ESF, equipment that is installed in private networks can also pro-

vide the same performance information to the user.

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ADTRAN TSU LT User Manual Page 13