A computer
data network is comprised of a number of components, including the computers
and other associated network attached devices. The computers and other
peripherals are usually connected to each other through a network switch or hub
and by means of copper electrical connections, fibre or by means of wireless.
The hubs or
switches normally provide local connectivity for the computer devices, in what
is normally referred to as a LAN (Local Area Network). LANs are normally
interconnected by means of routing devices, whether they are in a private
network or indeed the Public Internet. The purpose of a computer data network
is one of sharing and collaboration, where resources are made available by some
of the devices on the network for use by other devices.
In Peer-to-Peer
networks, individual devices offer resources to other peers on the network, but
there is no central control of these resources. Each peer can offer resources
such as disk space, files, or even processing power.
The Client
Server network model clearly distinguishes between client devices and server
devices. All clients, or selected clients can have access to resources hosted
on specific network servers, for example, an email server, http server or file
server. The client does not host any services, but merely requests a service
from a particular server device. Some servers often host and offer multiple
services to clients.
Data networks
are to be found in virtually every environment, not least of all our homes, as
most of us now have a connection to the Internet and run a small local network
ourselves. Almost all businesses also run data networks to provide employees
with connections to the Internet and to other sites owned by the business.
Components within a computer network fall into 4 main areas, and these are: the
computers and servers (sometimes referred to as host devices), interconnections
(comprising the cables or wireless medium), switches or hubs (which provide the
local connectivity and routers that enable Local Area Networks to communicate
with each other.
The purpose of
the computers is to host the private user information and also to provide a
data interface to the network itself, in order to be able to communicate with
other computers, or to connect to servers that provide information or provide
some other service to the client computer devices. There are many different
services or applications, with the most common coming under the headings of
Email, File Transfer, Collaboration, Instant Messaging, Voice and Media over IP
as well as the ability to access websites through the use of HTTP.
The Servers
allow the user to host a particular service such as a website with content for
clients to download, email system, information service, such as a database or a
storage system, where files can be made available for download.
The
interconnections predominantly fall into two main categories, Wired and
Wireless. Modern day wired connections between end user devices and the network
components are normally in the form of copper twisted pair cable, but coaxial
cable or fibre optic cable can also be used. Fibre optic cable is becoming more
popular, but at present it is normally used to provide higher bandwidth
connections between switches and routers in the network. The communications
fibre can provide extremely high bandwidth, when required and has the added
benefit of being virtually immunie from electromagnetic interference.
Most wireless
interconnections are governed by the IEEE 802.11 standards, and users will
normally access a wireless network by means of a wireless router or wireless
access point. Wireless local area networks (WLANs) are becoming extremely
popular, mainly due to the fact that the user is freed from the cumbersome cable
connection, but wireless networks also have their drawbacks. Because most
wireless networks use the unlicensed ISM (Industrial, Scientific and Medical)
frequency bands, interference from other users can be a problem at times, even
other adjacent wireless networks.
Data switches
forward the data traffic between end users and servers by using a unique
identification feature known as the MAC Address, allocated to each user
interface. A data switch builds up a table of all the connected user devices by
reading the MAC Address in the Ethernet frames sent by each device. The table
indicates to the switch the specific port of connection that each unique device
is attached to. The switch can therefore ensure data is forwarded to the
correctly addressed device. Some switches can provide a greater degree of
sophistication by allowing the configuration of a variety of features, such as
Quality of Service (QoS), port security, creation of Virtual Local Area
Networks (VLANs), port forwarding and many more.
Routers are
designed to provide interconnectivity between different networks or
sub-networks. This is achieved by addressing each device with a logical
address, the most common of which is the IP (Internet Protocol) address. A
router will build up a picture or map of all the available networks and router
IP packets between different networks by reading the destination IP address
within each data packet. In order to achieve this, local devices within a local
area network must have addresses that are within the same unique range. In
other words, they must have the same common network or sub-network identity.
Routers can also provide a greater degree of security by filtering traffic
between different local area networks or between different individual devices
on the network. 7
There are many
other devices on modern computer data networks, such as Firewalls, Proxy
Servers, Intrusion Detection Systems, Intrusion Prevention Systems to name just
a few.
We have come a
long way since those early networks back in the early 1980s, and today's
networks are becoming more and more sophisticated as time goes by. Real time
media and multimedia over data networks would be been near impossible 20 years
ago, but nowadays voice and video are common media carried across our computer
data networks.
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