7/27/2019 How Does a T1 Line Work

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How does a T1 line work?  

Most of us are familiar with a normal business or residential line from the phone

company. A normal phone line like this is delivered on a pair of copper wires (seeHow Telephones Work) that transmit your voice as an analog signal (see How

Analog and igital !ecording Works for details). When you use a normal modem ona line like this" it can transmit data at perhaps #$ kilobits per second (#$"$$$ bits

per second).

The phone company moves nearly all voice traffic as digital rather than analog

signals. %our analog line gets converted to a digital signal by sampling it &"$$$times per second at &'bit resolution ("$$$ bits per second). *early all digital data

now flows over fiber optic lines" and the phone company uses different designationsto talk about the capacity of a fiber optic line.

+f your office has a T, line" it means that the phone company has brought a fiberoptic line into your office (a T, line might also come in on copper). A T, line can

carry - digitied voice channels" or it can carry data at a rate of ,./ megabitsper second. +f the T, line is being used for telephone conversations" it plugs into the

office0s phone system. +f it is carrying data it plugs into the network0s router.

A T, line can carry about ,1-"$$$ bytes per second '' roughly $ times more data

than a normal residential modem. +t is also e2tremely reliable '' much more reliablethan an analog modem. epending on what they are doing" a T, line can generally

handle 3uite a few people. 4or general browsing" hundreds of users are easily ableto share a T, line comfortably. +f they are all downloading M5# files or video files

simultaneously it would be a problem" but that still isn0t e2tremely common.

A T, line might cost between 6,"$$$ and 6,"/$$ per month depending on who

provides it and where it goes. The other end of the T, line needs to be connected to

an +75 (see How the +nternet Works)" and the total cost is a combination of the feethe phone company charges and the fee the +75 charges.

A large company needs something more than a T, line. The following table shows

some of the common line designations8

• 7$ ' kilobits per second

• +7* ' Two 7$ lines plus signaling (, kilobytes per second)" or ,-&

kilobits per second

• T, ' ,./ megabits per second (- 7$ lines)

• T# ' #.-#- megabits per second (-& T,s)

• 9:# ' ,// megabits per second (& T,s)

• 9:,- ' -- megabits per second ( 9:#s)• 9:& ' -./ gigabits per seconds ( 9:,-s)

• 9:,1- ' 1. gigabits per second ( 9:&s)

Here are three interesting links8