Page 293 - Optical Communications Essentials

Optical Networks

Optical Networks 283

campus. Here the word campus refers to any group of buildings that are
within reasonable walking distance of each other. For example, it could be
the collocated buildings of a corporation, a large medical facility, or a uni-
versity complex. LANs usually are owned, used, and operated privately by
a single organization, which is referred to as an enterprise.
2. Metropolitan-area networks (MANs) span a larger area than a LAN. The
size of a MAN could range from interconnections between buildings cov-
ering several blocks within a city or it could encompass an entire city and
the metropolitan area surrounding it. There is also some means of inter-
connecting the MAN resources with communication entities located in
both LANs and wide-area networks. MANs are owned and operated by
many organizations. They commonly are referred to as metro networks.
3. Wide-area networks (WANs) span a large geographic area. The links can
range from connections between switching facilities in neighboring cities
to long-haul terrestrial transmission lines running across a country or
between countries. WANs are owned and operated by either private enter-
prises or telecommunication service providers.
4. Undersea networks (not shown explicitly in Fig. 17.1) use undersea cables
to connect continents. These cables could be several thousand kilometers
in length, such as those running across the Atlantic Ocean between North
America and Europe or those crossing the Pacific Ocean.
When a network is owned and deployed by a private enterprise, it is referred
to as an enterprise network. The networks owned by the telecommunication
carriers provide services such as leased lines or real-time telephone connections
to other users and enterprises. Such networks are referred to as public
networks.

17.1.2. Network terminology
Before we examine network details, let us define some terms, using Fig. 17.2 for
guidance.

■ Stations. Collections of devices that users employ to communicate are called
stations. These may be computers, terminals, telephones, or other equipment
for communicating. Stations are also referred to as data terminal equipment
(DTE) in the networking world.
■ Networks. To establish connections between these stations, one deploys trans-
mission paths running between them to form a collection of interconnected
stations called a network.
■ Node. Within this network, a node is a point where one or more communica-
tion lines terminate and/or where stations are connected. Stations also can
connect directly to a transmission line.
■ Trunk. The term trunk normally refers to a transmission line that runs
between nodes or networks and that supports large traffic loads.

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