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 Types Client 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 Types Peer 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 Server Peer 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 required Infrastructure may be required. Server failures have more impact

Network Hardware Servers Application Servers Communication 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.