By Kim Young Jun IGCSE1

 Computer network  Common types of network  Ring, bus, star and tree  Local are networks  Wide are networks  Wireless LANs (WLANs)  Network device  The internet  Intranet  Network security  Communication methods

Most computer systems are now connected together in some way to form what is known as a network. This ranges from the basic school/home network of only a few computers to large network such as the internet which effectively allows any computer connected to it to communicate with any other computer similarly connected.

 File servers, which allows users to save and load data/files.  Application servers, which deal with the distribution of applications software to each computer.  Printer servers, which ensure printing from devices on the network is done in a queue.  Proxy servers, which are used as a buffer between WANs and LANs.

Ring networks Being less popular. Every computer in the network is connected in a ring, including server. Bus networks Each computer or device is connected to a common central line. Data travels along this central line until it reaches the computer or device that requires it.

Star networks With a star network, each computer or device is connected via a central hub or switch. Data is sent to the hub which then sends out data along every cable to every computer or device. Tree network A tree network has a central line connecting together a series of star networks. The sever is also connected to this central line. Because of flexibility.

A local area network (LAN) is usually within on e building or certainly not over a large geographical area. A typical LAN will consist of a number of computers and devices which will be connected to hubs or switches.

A wide area network (WAN) is basically formed by a number of LANs being connected together through either a router or a modem. Some companies will set up private WANs. This is expensive but comes with the advantage of much enhanced security. It is more common to use an internet service provider (ISP) for connections to the internet and communicate via this network system.

WLANs are similar to LANs but there are no wires or cables. They provide wireless network communications over fairly short distances.

Modem means modulator and is a device which converts a computer’s digital signal into an analogue signal for transmission over an existing telephone line. It also does the reverse process, in that it converts analogue signals from a telephone line into digital signals to enable the computer to process the data.

Network hubs are hardware devices that can have a number of devices/computers connected to them. Its main task is to take any data received via one of the ports and then send out this data from all of the ports.

Switches are similar to hubs but are more efficient in the way they distribute data. Data packets sent to the switch will have a mac address giving the source and giving the source and receiving device.

Routers inspect the data packages sent to if from any computer on any of the networks connected to it. The router is able to send the data package to the appropriate switch and it will then be delivered using the mac destination address in the data packet.

Bridges are device that connect one LAN to another LAN that use the same protocol. They decode whether a message from a user is going to another user on the same LAN or to a user on a different LAN.

The internet is worldwide collection of networks which allows a subscriber to send and receive s, chat (using text or voice) or browse the world wide web. The world wide web (WWW or web) is the part of the internet which the user can access by way of a web browser.

The web is made up of millions of these websites and millions of web pages. Web pages are documents on a computer screen which may consist of text, pictures, sounds animation or video.

There are three common ways of accessing the internet offered by service providers:  Dial-up internet access  Cable internet access  Digital subscriber line (DSL) (broadband) internet access.

Many companies use an intranet as well as the internet. The simple definition of an intranet is a computer network based on internet technology that is designed to meet the internal needs for sharing information within a single organization/company.

The security problems when using networks such as the internet are well documented. There are various security threats to networks and there are many equally varied ways of combating the threat.  User ID  Password  Encryption  Authentication techniques

When logging on to any network system, a user will be asked to type in a user ID. This assigns the user privileges once the logon procedure is successful, who is able to set passwords, delete files from the server, etc. whilst a user privilege may only allow access to their own work area.

After keying in the user ID user will then be requested to type in their password. This should be combination of letter and numbers which would be difficult for somebody else to guess. When the password is typed in it often shows on the screen as******* so nobody overlooking can see what the user ca see what the user has typed in.

Encryption is the converting of data into a code by scrambling it or encoding it. This is done by employing encryption software. Since the data is all jumbled up it appears meaningless to a hacker or anyone who illegally accesses the data.

This is called authentication, and type of authentication is used in the banking example that follows. Most systems adopt the following authentication logic:  Something you know-e.g. PIN/password  Something belonging to you-e.g. your bank card  Something unique to you-e.g. your fingerprints.

Many methods of communication using networks exist. These include fax, , video conferencing and VOIP.

The term fax is short for the word facsimile. With the this system, documents are scanned electronically and converted into a bit map image. This is transmitted as a series of electrical signals through the telephone network. The receiving fax machine converts this electronic image and prints it out on paper.

This is an electronic method for sending text and attachments from one computer to another over a network.

This is a method of communication between people at two separate locations. This is done in real time and makes use of a LAN, if internal, or through a WAN. The system also uses special software such as:  CODEC, which converts and compresses analogue data into digital data to send down digital lines.  Echo cancellation software, which allows talking in real time and synchronises communications.

Voice over internet protocol (VOIP) is a method used to talk to people using the internet. VOIP converts sound into discrete digital packets which can be sent to their destination via the internet. The most prominent security issues over VOIP are:  Identity and service theft  Viruses and malware  Spamming  Phishing attacks