Bandwidth
Bandwidth is the capacity of a network connection to move information
(the size of the pipe, so to speak). Bandwidth is measured in Kbps
(kilobits per second) for slow connections, Mbps (megabits per second)
for faster connections such as DSL, cable, or Ethernet LAN connections,
and Gbps (gigabits per second) for the kinds of connections used
by huge corporations and Internet providers.
Bandwidth is a shared resource. If a network connection is
capable of transferring data at, say, 1.5 Mbps, and two
users simultaneously download large files, each will only
have roughly 0.75 Mbps (or 768 Kbps) of bandwidth at
their disposal.
Ethernet-based local networks can transfer data at up to 1,000 Mbps.
High-speed T1, DSL, and cable modem connections typically transfer
data up to 1.0 to 6.0 Mbps, while the fastest analog modems communicate
at a glacial 56 Kbps, or 0.056 Mbps.
To translate a bandwidth measurement into more practical terms, you??™ll
need to convert bits to bytes. There are 8 bits to a byte, so you can
determine the theoretical maximum data transfer rate of a connection
by simply dividing by 8. For example, a 384 Kbps connection transfers
384/8 = 48 kilobytes of data per second, which should allow you to
344 | Chapter 7: Networking and Internet
transfer a 1 megabyte file in a little more than 20 seconds. However,
there is more going on than just data transfer (such as error correction), so
actual performance will always be slower than the theoretical maximum.
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