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.
David Christie is MD at NSTUK Ltd, a Technical Training and Consultancy company based in the Northeast of England. David delivers technical training in the area of Data Communications and Telecoms and also provides consultancy and Training Needs Analysis. The company runs an ecommerce website specialising in the sale of Networking hardware and consumer electronics. Website: http://www.ipexpress.co.uk
