Networking: A Beginner's Guide
f you were to compare a computer network to the human body, the network cabling
system would be the nerves that make up the physical manifestation of the nervous
system. The network cabling system is what actually carries all the data from one
point to another and determines how the network works. How a network is cabled is of
supreme importance to how the network functions, how fast it functions, how reliable the
network will be as a whole, and how easy it will be to expand and change the network.
With any new network, your first task after assessing the needs for the network is to
determine how the network should be wired; all the other components of the network
are then built on that foundation. This is much like the OSI seven-layer model you
learned about in Chapter 3, in that the network cabling makes up layer 1 (the physical
layer), and all the upper networking layers rely on it.
Many people think that network cabling is relatively simple. After all, what could
be simpler than running a wire between two points? However, as you will see, the
topic of network cabling encompasses more than meets the eye, and it's an extremely
important area to get right. If you make mistakes selecting or installing network cable,
your network will likely be unreliable and may perform poorly. Because of the labor
costs involved in wiring a network, the best time to address any potential problems in
this area is well before they occur.
Understanding Cable Topologies
The word topology basically means shape, and the term network topology refers to the shape
of a network--how all of the nodes (points) of a network are wired together. Networks
may be wired in several different topologies, and the choice of a topology is often your
most important decision when you plan a network. The topologies have different costs
(both to install and maintain), levels of performance, and levels of reliability.
DEFINE-IT! Network Segment
The term network segment can mean somewhat different things depending on the
topology of the network, but the concept is simplest to understand when thinking
about a bus network, and is essentially the same for any topology. A segment is
a single length of cable to which all the nodes in that segment are connected. In
truth, a segment is not a single continuous length of cable, because it is broken at
each computer connection point with a connector that lets the node connect to the
network cable, but the cable is electrically one single cable.
In any given segment, all the network traffic is "seen" by all the nodes on that
segment. You need to take this into account when planning how many nodes you
will connect to any given segment. If you have 20 computers, all fully using that
segment at the same time, each computer will achieve only approximately one-
twentieth of the available maximum bandwidth. This is simplified; you will learn
more about how this works later in this chapter and in following chapters.