A TOPOLOGY is a map of a network. LOGICAL TOPOLOGIES
define how data flows within a network. PHYSICAL TOPOLOGIES are used to describe
the layout of cables, workstations and other NETWORK COMPONENTS. CABLES or CONNECTORS
in a physical topology are termed NETWORK MEDIA.
The four most common physical topologies that
are applied to a computer network are:
THE FOUR MOST COMMON PHYSICAL
TOPOLOGIES
In a bus topology all computers, and other network devices are attached, by DROP CABLES to a single, continuous cable that terminates at both ends.
Any communication that travels along the wire is "seen" by all other computers on the wire as it passes. Although, the only computer that actually receives the data is the one to which it is addressed. Think of it as two people talking to one another across a crowded room in which everyone else is having their own conversation. Only the two people actually involved in our conversation would be listening to what the other is saying.
It's benefits are that it is easy to install and, because of the small amount of network media to implement, it is relatively inexpensive. It's main drawbacks are that it is difficult to troubleshoot and not easily reconfigured. It is LOW FAULT TOLERANT. This means that it doesn't have any redundant connections that would keep the network up if the central cable that connects all of the network devices together malfunctioned.
When a star topology is utilized, cables radiate from a central point. This central point is a piece of hardware called a HUB. This hub facilitates communication between all network devices attached to it. It is easily reconfigured and trouble shot. Another added advantage of this topology is its heightened fault tolerance. If a cable or network device malfunctions the entire network does not go down; hub malfunctions are extremely rare. Because, of the cost of the hub and additional cabling, the downside of this topology is that it is more expensive then others.
In a ring topology each computer is connected to the one next to it. Imagine a group of people holding hands and you'll be visualizing a physical ring topology. The good news with this sort of layout is its' ease of installation; the bad news is that it is the least fault tolerant of all physical topologies. If a single cable or computer goes down so does the entire network.
In its' purest form a mesh topology connects
each station to every other station on its' network.
A mesh topology is the most complex
type of physical topology in that the wiring and connections increase exponentially.
For every n stations you have n (n-1) / 2 connections.
Remembering that n equals the number of stations on the network it solves
like this:
On a network with six computers:
6 (6-1) / 2
6 (5) / 2
30 / 2 =
15 connections
On a network with ten computers:
10 (10-1) / 2
10 (9) / 2
90 / 2 =
45 connections
As you can see the addition of four computers on a network that has six results in THIRTY more connections. So, while this sort of network is the most fault tolerant it is also the most expensive and difficult to maintain.
A variation on this, called HYBRID MESH is used on the Internet and some WANs in a limited fashion. In this variation multiple connection can exist between locations for the purpose of redundancy and higher fault tolerance. It isn't a true mesh because a connection does not exist between each and every NODE (or computer) on the network.
BACKBONES and SEGMENTS are terms used to more
intelligently identify parts of a network.
A backbone is the main structural part of a
network. It is usually a high speed connection technology of some kind and as
the name implies it is the main pipeline through which a network's data flows.
Servers and segments are directly connected to, and run off of, a backbone.
A segment is a general
term for any short section of the network that connects a network device to
the backbone.
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Back to The Nest
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