| 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 that transmit your voice as an analog signal. When you
use a normal modem on a line like this, it can transmit data
at perhaps 30 kilobits per second (30,000 bits per second).
The phone company moves nearly all voice traffic as digital
rather than analog signals. Your analog line gets converted to
a digital signal by sampling it 8,000 times per second at
8-bit resolution (64,000 bits per second). Nearly all digital
data now flows over fiber optic lines, and the phone company
uses different designations to talk about the capacity of a
fiber optic line.
If your office has a T1 line, it means that the phone
company has brought a fiber optic line into your office (a T1
line might also come in on copper). 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 or video files
simultaneously it would be a problem, but that still isn't
extremely common.
A T1 is a dedicated phone connection supporting data rates
of 1.544Mbits per second. A T-1 line actually consists of
24individual channels, each of which supports 64Kbits per
second. Each 64Kbit/second channel can be configured to carry
voice or data traffic. Most telephone companies allow you to
buy just some of these individual channels, known as
fractional T-1 access. It is a standard
for digital transmission in North America. A digital
transmission link with a capacity of 1.544 Mbps (1,544,000
bits per second.) T1 lines are used for connecting networks
across remote distances. Bridges and routers are used to
connect LANs over T1 networks.
A T1 is a digital transmission link with a capacity of
1.544 Mbps (1,544,000 bits per second). T1 uses two pairs of
normal twisted wires, the same you use in your house. T1
normally can handle 24 voice conversations with each
conversation being digitized at 64 Kbps. But, with more
advanced digital voice encoding techniques, it can handle more
voice channels.
A high-speed communications line, sometimes called T-1
carrier, originally developed to carry multiple conversations
over standard twisted-pair telephone wiring. Currently, T1
provides digital communications and Internet access at the
rate of 1.54 Mbps. T1 speed is attained through multiplexing
24 separate 64 kbps channels into a single data stream.
A large company needs something more than a T1 line. The
following list shows 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)
|