Slide 1

What is a Computer Network?

• A computer network is a linked set of computer systems capable of sharing computer power and resources such as printers, large disk drives, CD-ROM and other databases.

• There are two types of network: Local Area Network (LAN) Wide Area Network (WAN)

Slide 2

Local Area Networks

• A local area network is a computer network across one building or site.

Fileserver

Printer

Work Station

Network Cable

Slide 3

Peer to Peer Network

• This describes a very simple network structure where shared resources such as printers are available but where there are very few other facilities.

• All computers on the network have similar specification and status.

Slide 4

Client-Server Network

• This method of network organisation requires one or more servers to which a number of clients may obtain services.

• The servers act as central resource managers for the network.

• A star topology is often used for this form of network.

Slide 5

Network Hardware

• Network hardware will include: stations servers

• file, print, web passive components

• cables, connections, etc active components

• repeaters, hubs, switches

Slide 6

Network Stations

• The network station (often called the client) will normally comprise: PC Network interface card (NIC).

• The NIC allows the computer to communicate with the network

Network Operating Systems• eg. Windows 95/98, Windows NT,

Appleshare, etc

Slide 7

Network Servers

• A network server is a computer which acts as a central storage point for files and applications.

• Servers also act as a connection point to shared peripherals such as printers.

Slide 8

Active Components

• Active components are required for all but the simplest of networks.

• These include: repeaters hubs switches

Slide 9

Repeaters

• Due to loss of signal strength it is often necessary to use a repeater to boost the signal.

• A repeater is a hardware device to link together two cable segments.

• The repeater amplifies the signal it receives before passing it on.

Slide 10

Hubs

• A hub is a device which allows the interconnection of a group of users. A hub will forward any packet of data it receives over one port from one station to all of the remaining ports.

• Hubs are used in the star topology.

Slide 11

Switches

• A switch is “smarter” than a hub and offers more bandwidth. A switch forwards data packets only to the appropriate port for the intended recipient.The switch establishes a temporary connection between the source and the destination.

Slide 12

Routers

• A router receives packets of data transmitted over a network, and using their IP address, forwards them to the correct destinations over the most efficient available path.

Slide 13

Network Topologies

• The network topology is the theoretical arrangement of components on a network.

• There are four network topologies which you need to be aware of: bus star Ring mesh

Slide 14

Bus Topology

• Each device is connected to a main communications line called a bus.

Slide 15

Star Topology

• In the star topology all stations are connected to a central node, called a hub.

Slide 16

Ring Topology

• Each device is connected to a ring around which signals are sent. The devices are connected to the ring via spurs, or the connection may pass through the interface card

Slide 17

Mesh Topology

• A mesh network is the most expensive type of network to install

Slide 18

Protocols

• A protocol is a standard set of rules used to ensure the proper transfer of data between devices.

• In network design it is vital that a recognised protocol is used.

Slide 19

TCP/IP

• TCP/IP is a protocol which allows computer on different networks to communicate.

• TCP/IP is a pair of protocols TCP - transmission control protocol IP Internet Protocol

Slide 20

IP Addressing

• Every computer station on the internetwork must have an IP address.

• This IP address must be unique but is not encoded in the network interface. It is set by software in the computer.

Slide 21

Internetwork Hardware

• Connecting LANs together will require extra hardware: bridges routers gateways

Slide 22

Bridges

• A bridge acts as a link between LANs.

• This will allow two LANs to appear to users as though they are a single LAN.

Slide 23

Routers

• A router is a device which receives data packets and sends them on via an appropriate route.

• It will have a number of network interface ports to allow connection to different segments to which data packets may be directed.

Slide 24

Gateways

• A gateway is a link between two dissimilar networks..

• The communications between the networks are usually via public telecommunications networks.

• A gateway will normally be used to connect a LAN to the Internet.

Slide 25

Implications of Networks

• Computer networks have developed as a result of a perceived need and as a result of economic and technical factors.

• Computer networks have social, legal and ethical implications

Slide 26

Economic Factors

• The cost of communication technology equipment costs are continually reducing and

improving features mean that more is available for the same money.

• Access to expensive equipment printers and mass storage are expensive so it makes

sense to share them.

• Geographic spread of organsiations video-conferencing and email, etc allow

organisations to cope with geographic isolation.

Slide 27

Technical Factors

• Adoption of Internet technology TCP/IP

• Adoption of International Standards ISO OSI

• Development of Communication Technology fast modems, ISDN, etc

Slide 28

Social Implications

• Individuals may become withdrawn from society

• Personal privacy may be compromised as a result of monitoring network use

• People may not have to move from rural communities to find

• Home working may allow strengthening of family life (?)

Slide 29

Ethical Implications

• Bogus doctors could easily offer medical advice over the Internet.

• Availability of unacceptable and inappropriate material within education

• Antisocial, criminal, racist or other prejudiced material may be distributed freely.

Slide 30

Legal Implications

• Copyright law British law makes it illegal to copy

someone elses copyright material. A lot of material on web pages is copyright Sometimes the breaking of this law is unwitting but in others it is deliberate (eg MP3 files of commercial recordings)