تاريخ التسجيل: 2007-07-23
مشاركات: 483
الجامعة: حلب
الاختصاص: هندسة شبكات
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Wide Area Network
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Chances are you are an experienced
wide area network (WAN)
user and don’t even know it. If
you have ever connected to the Internet, you have used the largest WAN on the planet. A WAN
is any network that crosses metropolitan, regional, or national boundaries. Most networking
professionals define a WAN as any network that uses routers and public network links. The
Internet fits both definitions.
WANs differ from LANs in the following ways:
WANs cover greater distances.
WAN speeds are slower.
WANs can be connected on demand or permanently connected; LANs have permanent
connections between stations.
WANs can use public or private network transports; LANs primarily use private network
transports.
WANs can use either full- or half-duplex communications. LANs have typically used halfduplex
communications, although many local area networks today use full-duplex communications
(see the sidebar “Full-Duplex vs. Half-Duplex Communications”).
The Internet is actually a specific type of WAN. The Internet is a collection of networks that
are interconnected and, therefore, is technically an
internetwork
(
Internet
is short for the word
internetwork
).
A WAN can be centralized or distributed. A centralized WAN consists of a central computer (at
a central site) to which other computers and dumb terminals connect. The Internet, on the other
hand, consists of many interconnected computers in many locations. Thus, it is a distributed WAN.
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Local Area Network
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By definition, a
local area network (LAN)
is limited to a specific area, usually an office, and cannot
extend beyond the boundaries of a single building. The first LANs were limited to a range
(from a central point to the most distant computer) of 185 meters (about 600 feet) and no more
than 30 computers. Today’s technology allows a larger LAN, but practical administration limitations
require dividing it into small, logical areas called workgroups.
A
workgroup
is a collection of individuals (a sales department, for example) who share the
same files and databases over the LAN. Figure 1.1 shows an example of a small LAN and its
workgroups.
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