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Short for
asymmetric digital subscriber line, a new technology that allows more data
to be sent over existing copper telephone lines (POTS).
ADSL supports data rates of from 1.5 to 9 Mbps when
receiving data (known as the downstream rate) and from 16 to 640 Kbps when
sending data (known as the upstream rate). |
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ADSL is growing in popularity as more areas around the world gain access. |
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POTS |
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Short for
plain old telephone service, which refers to the standard telephone
service that most homes use. In contrast, telephone services based on
high-speed, digital communications lines, such as ISDN and FDDI, are not
POTS. The main distinctions between POTS and non-POTS services are speed
and bandwidth. POTS is generally restricted to about 52 Kbps (52,000 bits
per second). |
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The POTS
network is also called the public switched telephone network (PSTN). |
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POTS should
not be confused with pot, an abbreviation of potentiometer. |
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Data
Transfer Rate |
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The speed with which data can be transmitted from one device to another.
Data rates are often measured in megabits (million bits) or megabytes
(million bytes) per second. These are usually abbreviated as Mbps and
MBps, respectively. |
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Mbps |
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(1) When
spelled Mbps, short for megabits per second, a measure of data transfer
speed (a megabit is equal to one million bits). Network transmissions, for
example, are generally measured in Mbps. |
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(2) When
spelled MBps, short for megabytes per second. |
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Kbps |
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Short for kilobits per second, a measure of data transfer speed. Modems,
for example, are measured in Kbps. Note that one Kbps is 1,000 bits per
second, whereas a KB (kilobyte) is 1,024 bytes. Data transfer rates are
measured using the decimal meaning of K whereas data storage is measured
using the powers-of-2 meaning of K. Technically, kbps should be spelled
with a lowercase k to indicate that it is decimal but almost everyone
spells it with a capital K. |
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Digital |
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(adj.)
Describes any system based on discontinuous data or events. Computers are
digital machines because at their most basic level they can distinguish
between just two values, 0 and 1, or off and on. There is no simple way to
represent all the values in between, such as 0.25. All data that a
computer processes must be encoded digitally, as a series of zeroes and
ones |
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The opposite
of digital is analog. A typical analog device is a clock in which the
hands move continuously around the face. Such a clock is capable of
indicating every possible time of day. In contrast, a digital clock is
capable of representing only a finite number of times (every tenth of a
second, for example). |
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Communications |
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The transmission of data from one computer to another, or from one device
to another. A communications device, therefore, is any machine that
assists data transmission. For example, modems, cables, and ports are all
communications devices. Communications software refers to programs that
make it possible to transmit data. |
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ISDN |
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Abbreviation of integrated services digital network, an international
communications standard for sending voice, video, and data over digital
telephone lines or normal telephone wires. ISDN supports data transfer
rates of 64 Kbps (64,000 bits per second). |
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There are two types of ISDN: |
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Basic Rate
Interface (BRI) -- consists of two 64-Kbps B-channels and one D- channel
for transmitting control information.
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Primary
Rate Interface (PRI) -- consists of 23 B-channels and one D-channel (U.S.)
or 30 B-channels and one D-channel (Europe).
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FDDI |
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Abbreviation
of Fiber Distributed Data Interface, a set of ANSI protocols for sending
digital data over fiber optic cable. FDDI networks are token-passing
networks, and support data rates of up to 100 Mbps (100 million bits) per
second. FDDI networks are typically used as backbones for wide-area
networks. |
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An extension
to FDDI, called FDDI-2, supports the transmission of voice and video
information as well as data. Another variation of FDDI, called FDDI Full
Duplex Technology (FFDT) uses the same network infrastructure but can
potentially support data rates up to 200 Mbps |
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NEXT ... |
