Computer communication

Networks

Specification Requirements

Candidates should be able to: • describe the hardware needed to connect

stand-alone computers into a local area network, including hub/switches, wireless access points

• explain the different roles of computers in a client-server and a peer-to-peer network

• describe, using diagrams or otherwise, the ring, bus and star network topologies

Network Hardware

Network interface card: • A network adapter such as a network

interface card (NIC) is needed to connect computers and other peripherals to a network, either by cable or wirelessly. Each connected device is allocated an IP address to uniquely identify it on a TCP/IP network.

Network Hardware

• Terminator– Device attached to the end of bus network– Prevents signals from bouncing

Network Hardware

• Repeaters– Signals can lost integrity, become attenuated

over long distances– Repeaters clean the signal up, then sends it

on.

Network Hardware

• Hubs– Effectively repeaters– Sends signal to all devices connected to it– Only intended receiver will process it– Used in star networks– Not good for large networks – collisions– Whole network goes down if Hub is broken

Network Hardware

• Bridges– Connects different network segments together– Can speed up a networks performance– Only sends on to different segments,

determined by reading MAC address– If not different segment then packet is

discarded clearing up traffic.

Network Hardware

• Switches– High Speed Bridge– Has a dedicated CPU– Intelligently determines route of packet to

destination

Network Hardware

• Twisted pair Cables– are the most common and is often called

Ethernet cabling. Category 5 (Cat5) twisted-pair cables can carry 100Mb per second over distances of up to 100 metres.

Network Hardware

• Coaxial cable– is better at resisting electrical interference so

it can be installed over longer lengths, but it is not as flexible.

Network Hardware

• Fibre Optic Cable– has a central glass core and transmits signals

using light at extremely high speeds over huge distances. It can be used outside buildings but it is significantly more expensive to purchase and install.

Network TypesClient Server• On a client-server network there are two types of computers with two distinct

roles. One or more server computers have the role of controlling access to shared resources like files and printers. Multiple client computers are then connected to the server computers and these are where the user works.

• The user typically logs onto a client computer which then connects to the server, verifies the user and then allows them access to the files and software stored on the server that they have permission to access.

• All the data is stored on the servers, which generally have far greater security controls than the client computers. Since data storage is centralised, security is easier to manage, updates to the data are far easier to administer and it is far easier to backup the data centrally.

• Some servers may have a more specialised role such as a print server, dedicated to controlling access to shared printers on the network and queuing print jobs in the order that they were sent by the users.

Network TypesPeer to Peer• In a peer-to-peer network computers are simply linked together, either using

cables and a hub or wirelessly.

• Such networks do not have computers with particular roles, instead, each computer can simultaneously act as both a client and a server, and each has equivalent responsibilities and status.

• This means that any computer on the network can load information from the hard disk of any other computer and a computer on the network can use any printer connected to any other computer.

• A peer-to-peer network will be cheaper to set up and, provided there are only a small number of computers, will be easier to manage than server based networks.

• However they are less secure and peer-to-peer networks are used mainly by home users and small companies who do not have the necessary technical staff to maintain a client-server network.

Network Types

Peer to Peer Vs Client ServerPeer to Peer Client Server

No network wide security Central control of security.

Soon become unworkable Easier to supervise network performance

Machines slow down when being accessed by others

Easier to perform software upgrades

Machines holding data being accessed can be restarted

Faster performance – fewer data collisions

Difficult to keep track of who has what information

Client machines freed up

Backup becomes complicated Easier to perform back-ups

Expensive to set up and good expertise requiredInfrastructure may be required.

Server failures have more impact

Network Hardware

• Servers– Application Servers

• DBMS Systems and other software

– Communication Servers• Entry point to network for external users

– File and Print Servers• Stores of data and access to printers

– Mail Servers• Access to email.

– Web servers• Allows intranets• Contains devices such as webcams, routers etc.