This guide will cover the following areas.
Introduction: The two main types of network
A computer network is the linking of two or more devices
for the purpose if effective communication.
There are two main types of computer network - both have a number of
elements in common. Each device on
the network is considered a node and these nodes are connected in some way to
enable communication.
The first type of network that a new user is likely
to encounter is called a peer-to-peer network.
In this type, no node is considered more important than another is and
each one has equal access to network resources. There is no single node that is able to control the network.
Examples of peer-to-peer networks include:
- PC
to Printer
- PC
to PC, (i.e. Internet share cross-over link)
A peer-to-peer network is useful only up to a point.
After about the twelve-user mark the network will start to experience
increasing difficulties in administration and control.
However, for low traffic file sharing on small networks this type can be
ideal.
The second type of network that the user is likely
to encounter is a Client-Server network.
With this type, the network is controlled by one or more servers with
all other nodes acting as clients.
This networking type has distinct advantages allowing the
network to become much larger while adding to the functional benefit of a
network.
Some examples of Client-Server networks include:
The primary advantage of Client-Server is this: control
Client-Server allows control over users access to network
facilities and data. This
effectively means that networks, with the added security of control, are now a
viable, large-scale business tool.
Network Topologies
Any given network can be said to have a topology of one
sort or another. A network’s
topology is the logical layout of the connectivity of the nodes. The exact configuration of the topology will affect the type
of protocol or rules used in network communication.
For the purpose of this guide, we will consider that there
are five main types of network topology.
Bus
With a bus-topology, a single main line or backbone runs
the length of the network. Each node
connects to this backbone and all communication must happen over it.
This means that only one device can transmit at any given moment.
When more than one device transmits at the same time the message becomes
garbled and a data collision is said to occur.
[PC] [PC] [PC] [PC]
| | | |
|-+----+----+----+-|
At each end of the bus is a terminator that will indicate
the end of the line stopping messages from endlessly travelling up and down the
bus.
Having only one device able to transmit at a time clearly
limits the scalability of bus networks but this has not stopped bus style
architecture from enjoying a time of unrivalled success as the cheapest and most
efficient network architecture. It
was here that Ethernet standards developed.
Due to the drawbacks of bus architecture as an organisation
grows in size they must employ ever more ingenious methods of maintaining the
network or move to another architecture.
Ring
The ring-topology answers some of bus architectures biggest
drawbacks by adding a method of control.
Here is a simple ring:
[PC]----------[PC]
| |
[PC] [PC]
\____[PC]____/
Under the token-ring protocol, (the main implementation
of early rings), a token is passed from computer to computer giving each the
chance to transmit. This removes
the data collision, but for larger networks the data rate slowly drops with each
additional node.
Ring topology also suffers from another physical
limitation – just as a bus requires two terminators, the ring requires an
unbroken loop or effective communication is broken.
Mesh
The mesh-topology provides durability lacking in ring and
scalability lacking in bus. Under
a mesh-topology, each node is connected to many other nodes.
The main communication device must be a level three device capable of
making complex routing decisions for the delivery of data packets.
The main draw back is the financial practicality of
implementing a mesh network. There
is no centre of control and the network may become fragmented and
repetitious with infinite-loops, dead-ends and lost packets clogging up the
system.
Mesh-topology works best with MAN and WAN sized
networks like JANET, Kentish-MAN and the Internet.
-
MAN: Metropolitan Area Network
-
WAN: Wide Area Network
-
JANET: Joint Academic NETwork (a UK MAN formed between
leading universities)
-
Kentish-MAN: A MAN project in Kent, England
-
Internet: A network of networks that allows such things
as: the World Wide Web and universal email.
Star
Star-topologies solve the complexity of mesh while
maintaining some of its better features.
In a star-topology all of the nodes are connected to some
form of central hub this is usually a switch or sometimes a router, but in times
not so long passed it may have been a multiport repeater.
[PC]
|
[PC] |
\____[hub]___[PC]
/ \
/ \
[PC] [PC]
A star is limited only by the number of ports in the hub
device and the quality and aforethought of the rooms cabling.
Stars are perfect for networks that fit into a room or two.
The moderately gifted reader will recall that it has been
suggested that the better features of mesh are retained by star and this is true
for a hierarchy of computer systems can be created where are star network ends
not in a PC or similar node but with another star network.
In this way, a pyramidal hierarchy that sometimes closely mimics management
structure can be achieved.
Hybrid or Tree
However, when the powerful simplicity of star is combined
(with modern communications equipment) with the ideas of each of the other
topologies is the true power of networking realised.
This method is sometimes called tree as the diagram of bus
plus star looks very much like a tree.
In this illustration we can see five different servers
making use of a bus topology (some via a ring) in order to serve users on a star
network.
[Accounts]---[CAD]
[Users] | |
V | |
>+< [File]-+-[Mail]
| [WWW] |
\________|_________/
The device that makes this possible is called a bridge.
A bridge device (including many routers) links two networks and
translates between protocols.
In this situation it is important to realise that the bus
would not be the now redundant 10 Mega-bite Ethernet but is likely to be fibre
and running at a gigabit or more. Similarly,
the ring for the servers is likely to be notably faster than the upper limit
required by the network.
Network Operating Systems
- What
is a network operating system?
- Different
kinds of NOS and their respective traits.
What is a network operating system?
A network operating system (NOS) or “extended operating
system” is much like any other with respect to the workstation but it has
the added power to extend the influence of the computer onto the network.
A good NOS will cause the computer to become less like an independent
device and more a part of a great whole.
Different kinds of NOS and their respective traits.
There are a large number of network operating systems
available for the average computer.
- The
Windows Suite
- Linux,
Unix and the like
- Others
including Mac
The Windows Suite
This include NT, 2000 and the many different server
specific OS. The windows suit of
server applications and specialised server operating systems present a dazzling
array of choices to the inexperienced network manager. Most have some use, many are best forgotten and some are
actually worthwhile.
With so much potential power and so many specialised server
OS in the Windows range it is unsurprising that Windows is considered very
flexible and horribly vulnerable. The
situation is not as bad as it once was but huge gaps are discovered daily
meaning that implementation is usually steady, deliberate, carefully considered
and usually really quite simple.
Compared to the leading rival (Linux) windows is by far
the easiest to configure and clearly in second place security wise.
However, despite some shortcomings Windows is well documented and
supported. Windows also benefits
from being familiar to many users.
Linux, Unix and the like
Often simply called “*nix” this range of OS are
developed free of charge under the banner of open source development.
From the onset this range of OS were designed to be multi-user, network
operating systems.
Linux now comes in a number different “flavours” some
of which are better suited to different tasks.
Debian is generally considered
to make the best server. There is
no range of OS just one all purpose freely available and highly acclaimed OS. Debian Linux is considered to be the most stable and secure of the Linux
distributions. However many people
find the slower and more through pace of development not to their taste.
Others including Mac
There are other less well-known NOS including Novell Netware and Mac OS
for the Apple Mac range of PCs. (There
is also a Linux designed for Macs).
There will always be marginalized alternatives some of
which may gain popularity (or at least refuse to die like Novell netware) while others (like a certain abortive Apple-Linux) fall by the way side.
Almost all make use of the same protocols, (Namely TCP/IP), and are
designed to use hybrid and star topologies and do so more effectively than on
others.
Conclusion: Summary of networking
It can be said, therefore, that there are three main areas
of consideration with any network:
The choice in any category will influence heavily the
available choices that can be made in the others.
Further Reading:
The budding network designer may wish to additional review: