ADTRAN 1204006L1 Manual do Utilizador descarregar pdf (Página 34)

Chapter 1. Introduction

1-4 TSU IQ+ User Manual 61200275L1-1

T1/FT1 OVERVIEW

The telephone companies (telcos) have used T1 digital

communications links for voice transmission since the early sixties.

The D4 channel bank is an example of a T1 digital carrier system

that was introduced inthe mid-seventies and is still widely usedby

the telcos. Communication demands of businesses continued to

grow to the point that the telcos beganoffering 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 development 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 the service providers deliver to the user

over two pairs of wires. The signal operates at 1.544 Mbps and is

usually extended by repeaters that are installed about every mile

after the first 6000 feet. The T1 signal isdivided into 24 time slots or

digitalsignal level zeros(DS0s)which operateat 64kbps.Each time

slot is occupied by digitizedvoice 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

facility datalink (FDL). Theservice providers originally usedESF to

monitor the performance of their service offering. Since the

introduction of ESF, equipment that is installed in private networks

can also provide the same performance information to the user.

Fractional T1

Fractional T1(FT1) lets the buyerpurchase less thana fullT1 circuit

between two points. Most carriers offer fractional T1 in increments

of 56or 64kbps. Connection is made to thesamenetwork elements.

The network allows multiple users to share the same interoffice T1

bandwidth.

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ADTRAN 1204006L1 Manual do Utilizador Página 34