Content









2.2
Types
of Networks



2.2.2
Local-Area Networks (LANs)





Local-area networks (LANs) connect many
computers in a relatively small geographical area such as a home, an
office, a building, or a campus (see Figures
and
). The
network connects each computer to each of the others by using a
separate communications channel. A direct connection from one computer
to another is called a point-to-point link. If the network were
designed using point-to-point links, the number of links would grow
rapidly as new computers were added to the network. For each computer
added, the network would need a separate connection to each of the
other computers. This approach would be very costly and difficult to
manage.
Starting in the late 1960s and early
1970s, network engineers designed a form of network that enabled many
computers in a small area to share a single communications channel. By
allowing the computers to share a communications channel, LANs greatly
reduce the cost of the network. Point-to-point links are used to
connect computers and networks in separate towns, or cities, or even
across continents.
The general shape or layout of a LAN is
called its topology. When all the computers connect to a central
point, or a hub, the network is a star topology. Another topology
connects the computers in a closed loop, where a cable is run from one
computer to the next and then from the second to its neighbor until
the last one is connected back to the first. This forms a ring
topology. A third type, called a bus topology, attaches each computer
into a single, long cable. Each topology has its benefits and
drawbacks. Today, most LANs are designed using some form of star
topology, although ring and bus layouts are still used in some
installations.
Whatever the topology of the network,
all LANs require the networked computers to share the communications
channel that connects them. The communications channel that they all
share is called the medium. It is typically a cable that carries
electrical signals through copper, or it may be a fiber optic cable
that carries light signals through purified glass or plastic. In the
case of wireless networks, the computers may use antennas to broadcast
radio signals to each other.
On a LAN, the rules for coordinating
the use of the medium are called the Media Access Control (MAC). Since
there are many computers on the network but only one of them can use
the medium at a time, there must be some rules for deciding how they
will take turns to share the network. The MAC rules allow each
computer to have its turn to use the medium so that there is a fair
and efficient way to share the network. In the case of conflicts when
more than one computer is contending for the media, the rules ensure
that there is an agreed method for resolving the conflict. In later
sections of this chapter, the major types of LANs will be reviewed,
including their rules for sharing the medium.




















Interactive
Lab Activity 
(Flash, 366 KB) 



 


Identify LAN Topologies and Devices