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Wide area networks (WANs) connect computers and
other devices separated by very large distances.
WANs support data transmission between cities,
states, and/or countries. For example, a
multinational corporation with offices in New
York and Seattle might use a WAN to connect two
or more LANs. Although WANs support transmission
of many of the same types of applications as
MANs, they typically do so at a much lower
speed. For example, two of the more common line
speeds used in WANs are 1.544 Mbps (T1)17
and 44.746 Mbps (T3).18
17
T1 — United States digital communication line
operating at 1.544 Mbps.
18
T3 — United States digital communication line
operating at 44 Mbps.
Private19
WANs have steadily grown in popularity because
they offer flexibility, security, and control
over internal data communications. During the
late 1960s through the 1970s, WANs based on
IBM’s SNA, and TCP/IP or X.25 packet switching
dominated the corporate scene. WANs built at
this time were comprised of such components as
terminals, processors, modems, multiplexers,20
concentrators,21
and communications links. Efficiency and speed
were less important in these early WANs than
cost-effective connectivity. The most common
applications involved connecting users to remote
resources to perform tasks like database
retrieval and maintenance, batch file
processing, on-line data entry, and so on. These
applications are much less time sensitive than
the demanding applications of today (e.g.,
videoconferencing). The most commonly used
communication link was the T1, which was used to
build large corporate WAN backbone networks. A
“backbone” typically consists of a collection of
high-speed lines — i.e., T1s — that transmit and
consolidate traffic from a number of other lines
operating at lower speeds. The lower-speed,
dedicated lines were typically used to transmit
data to and from mainframes and dumb terminals,
at a rate of 9.6 Kbps or 19.2 Kbps. The
consolidation of traffic onto lines with a
larger capacity offered many throughput and cost
advantages over many lines with smaller
capacity. WAN networks such as these flourished
as T1 costs steadily declined over the years.
19
Private — Communications facilities that are
used exclusively by the organization that owns
or leases them.
20
Multiplexer — Also known as a “mux,” this is a
device that allows more than one signal to be
sent over a channel simultaneously.
21
Concentrator — A device that consolidates
traffic coming from a number of circuits onto
a smaller number of circuits; used to reduce
costs.
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