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Networking
Technologies
CERTIFICATION OBJECTIVES
1.01
Networks
Two-Minute Drill
Q&A
Self Test
1.02
Topologies
1.03
Network Types
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Chapter 1: Networking Technologies
T
his chapter offers a brief introduction to networking and some basic networking terms
CERTIFICATION OBJECTIVE 1.01
Networks
A
network
is basically all of the components (hardware and software) involved in
connecting computers across small and large distances. Networks are used to provide
easy access to information, thus increasing productivity for users. This section covers
some of the components involved with networking, as well as the basic types of
topologies used to connect networking devices, including computers.
Components
One of the main components of networking is applications, which enable users to
perform various tasks. Many applications are
network-aware.
These applications allow
you to access and use resources that are not located on your local computer. Some of
the more common networking applications include e-mail (sending mail electronically),
FTP (transferring files), and WWW (providing a graphical representation to information).
The number of networking applications ranges in the thousands, but those listed are the
most commonly used.
To build a network, you need three types of devices or components: computers,
networking devices, and cabling. Computers—devices such as PCs and file servers
running Microsoft Windows, Macintosh OS, Unix (including Linux), or other
operating systems—are responsible for providing applications to the users. Networking
devices—such as hubs, bridges, switches, routers, firewalls, modems, NT1s (an ISDN
network termination device), and channel service units / data service units (CSU/
DSUs)—are responsible for moving information between computers.. Cabling, such
as copper or fiber cabling, is needed to connect the computers and networking devices
so that information can be shared between components. Wireless communication also
falls in this category.
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and concepts. This material should be a review of many already known concepts. You
should be familiar with the various networking topologies used in networks, as well as
different types of networks, such as local area networks (LANs) and wide area networks (WANs).
Topologies
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TABLE 1-1
Term
Definition
Networking
Locations
Small office/home office
(SOHO)
Users working from a home or small office (a handful of
people)
Branch office
A small group of users connected in a small area, called
a LAN, geographically separated from a corporate office
Mobile users
Users who can connect to a network from any location,
LAN or WAN
Corporate office
The location where most users in an organization and
their resources are located
Locations
Network components can be located in various locations. Table 1-1 shows some
common terms used to describe the location of network components.
CERTIFICATION OBJECTIVE 1.02
Topologies
When you are cabling up your computers and networking devices, various types of
topologies can be used. A topology defines how the devices are connected. Figure 1-1
shows examples of topologies that different media types use.
A
point-to-point
topology has a single connection between two devices. In this
topology, two devices can directly communicate without interference from other
devices. These types of connections are not common when many devices need to be
connected together. An example of a point-to-point topology is when you connect
two routers across a dedicated WAN circuit.
In a
star
topology, a central device has many point-to-point connections to other
devices. Star topologies are used in environments where many devices need to be
connected. An example of a media type that uses a star topology is 10BaseT Ethernet.
When connecting devices together, you connect your computers to a hub or switch
(the center of the star). An extended star topology is basically multiple star topologies
interconnected.
A
bus
topology uses a single connection or wire to connect all devices. Certain
media types, like 10Base5 and 10Base2 Ethernet, use a bus topology. Typically, special
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Chapter 1: Networking Technologies
FIGURE 1-1
Network topologies
types of connectors or transceivers are used to connect the cables in order to provide
the bus topology. In 10Base2, for example, each device connects to a single strand of
coaxial cable via a vampire tap. This device taps into the single strand of coaxial cable
and provides the physical connection from a networking device to the single strand
of cable.
In a
ring
topology, device one connects to device two, device two connects
to device three, and so on to the last device, which connects back to device one.
Ring topologies can be implemented with a single ring or a dual ring. Dual rings are
typically used when you need redundancy. For example, if one of the devices fails
in the ring, the ring can wrap itself, as shown in Figure 1-2, to provide a single,
functional, ring. Fiber Distributed Data Interface (FDDI) is an example of a media
technology that uses dual rings to connect computer devices.
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Topologies
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FIGURE 1-2
Dual rings and redundancy
Physical Versus Logical Topologies
A distinction needs to be made between physical and logical topologies. A
physical
topology describes how devices are
physically
cabled together. For instance, 10BaseT has
a physical star topology and FDDI has a physical dual ring topology. A
logical
topology
describes how devices communicate across the physical topology. The physical and
logical topologies are independent of each other. For example, any variety of Ethernet
uses a logical bus topology when devices communicate. This means that in Ethernet,
you might be using 10BaseT with a physical star topology to connect devices together;
however, these devices are using a logical bus topology to communicate.
Token Ring is actually a good example of a media type that has a different
physical topology from its logical one. Physically, Token Ring uses a star topology,
similar to 10BaseT Ethernet. Logically, however, Token Ring devices use a ring
topology to communicate. This can create confusion when you are trying to
determine how devices are connected together and how they communicate. FDDI,
on the other hand, is straightforward. FDDI’s physical and logical topologies are
the same: a ring. Table 1-2 shows common media types and their physical and
logical topologies.
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