T1 Lines

There can be two different lines offered from a phone company: a normal business line/ residential line & a T1 line. A normal phone line is usually a pair of copper wires that transmit voice as an analog signal. When you use a normal modem on a line like this, it can transmit data at 30 kb/second.

Now a days, all voice traffic is digital rather than analog signals and flows over fiber optic lines with different designations of capacity.

A T1 line means that the phone company has brought a fiber optic line into your office. A T1 line can carry 24 digitized voice channels, or it can carry data at a rate of 1.544 megabits per second. If the T1 line is being used for telephone conversations, it plugs into the office's phone system. If it is carrying data it plugs into the network's router.

A T1 line can carry about 192,000 bytes per second -- roughly 60 times more data than a normal residential modem. It is also extremely reliable -- much more reliable than an analog modem. Depending on what they are doing, a T1 line can generally handle quite a few people. For general browsing, hundreds of users are easily able to share a T1 line comfortably. If they are all downloading MP3 files or video files simultaneously it would be a problem, but that still isn't extremely common.

Here are some of the common line designations:

• DS0 - 64 k­ilobits per second
• ISDN - Two DS0 lines plus signaling (16 kilobytes per second), or 128 kilobits per second
• T1 - 1.544 megabits per second (24 DS0 lines)
• T3 - 43.232 megabits per second (28 T1s)
• OC3 - 155 megabits per second (84 T1s)
• OC12 - 622 megabits per second (4 OC3s)
• OC48 - 2.5 gigabits per seconds (4 OC12s)
• OC192 - 9.6 gigabits per second (4 OC48s)

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