Higher Computing

Networking

What we need to know!• Comparison of LANs, WANs, Intranet and Internetwork in terms of transmission media,

bandwidth, geographical spread and functions.• Distinction between a mainframe with terminals and a network of computers • Descriptive comparison of peer-to-peer networks and client server networks • Description of the functions of file, print and web servers • Description of a node and a channel • Description of bus, star, ring and mesh topologies using the terms node and channel • Description of the consequences for each of the above topologies of node and channel

failure • Simple description of the functions and uses of a hub, switch and router • Identification of the need for a network interface card (NIC) • Description and explanation of the trends towards higher bandwidth and

wireless communications • Description of the following technical reasons for the increasingly widespread use of

networks: advances in computer hardware, including processors, main memory capacity, backing storage, data transfer rates improved network related software, including browsers and network operating systems

• Description of the misuse of networks for the following illegal purposes: breaching copyright, hacking and planting viruses

• Description of the application of the Computer Misuse Act, the Copyright Designs and Patents Act and the Data Protection Act to the misuse of networks

Definitions

• A Network is 2 or more computers linked together is such a way that the can communicated with each other.

• A Local Area Network (LAN) covers a small area such as a room or building.

• A Wide Area Network (WAN) covers a widespread geographical area.

• An Intranet is a private network belonging to a company or organisation.

• An Internetwork is a collection of 2 or more Local Area Networks.

Definitions Cont.

• Terminals are composed of a monitor and keyboard with little or no memory/processing power. A terminal is used as an access point to a mainframe.

• Mainframes are powerful computer systems designed to provide:– High Capacity I/O capability (to deal with many

users)– High speed processing.– Centralised storage– High Availability (24 hours a day)– Thorough backup, recovery and security systems.

Local Area Networks

• Functions– Sharing of data files, peripherals, enabling

communication via emails.

• Geographical Spread– Limited to 1 building such as a school, office block or

factory.

• Transmission media– Twisted-pair copper cable, fibre-optic cable, co-axial

cable.

• Bandwidth– LANs have high bandwidth, typically 100-1000Mbps

although this depends on the transmission media.

Wide Area Networks• Functions

– Supports transfer of files, communication via email, shared use of multi-user databases, conferencing.

• Geographical Spread– No limit to the spread. I could cover a city/country or the world.

• Transmission media– The media may be a combination of twisted-pair copper cable,

fibre-optic cable and wireless.

• Bandwidth– The bandwidth available depends on the nature of the link. If you

are connected to a WAN using a dial-up modem you are limited to 56kbps. An ISDN line supports 64Kbps and a leased telecoms T3 line supports a 44.7Mbps transmission.

Intranet

• Functions– Internal email, sharing data files, web pages. E.g.

internal job adverts or sharing designs of products.• Geographical Spread

– No limit to the spread. I could cover a city/country or the world.

• Transmission media– Intranets use the same technologies as WANs to

cover large distances.• Bandwidth

– Intranets use the same technologies as WANs to cover large distances.

Internetwork• Functions

– An internetwork consists of several networks joined by devices such as routers or switches. The functions available are the same as those on a LAN.

• Geographical Spread– An internetwork can vary in its geographical spread from

linking LANs in a factory to linking WANs across several countries.

• Transmission media– This depends on the configuration of the internetwork. If it

connects several LANs in the same location then it may use a high speed backbone such as fibre-optic cable. If it covers a wide area then it would use a form of broadband.

• Bandwidth– Fibre-optic cable would allow a bandwidth up to 100Gbps.

Using broadband connections would give the performance of a WAN.

Peer-to-peer Network

• In this network, computers are managed independently. • They all have equal status for sharing resources and key

operations E.g. Validating users.• Each workstation can make its resources

(files/printers/disks) available so others can access them transparently.

• There is no centralised storage.• Backup can therefore be very difficult as each

workstation is independent.• Security is difficult to implement as no workstation can

take control of others. Each workstation can setup Usernames/Passwords.

• This network is best suited where everybody trusts each other. E.g. a family home.

Client-server Network• This network is made up of a client (A

workstation operated by a user) and a Server (a computer which controls a resource on the network).

• All resources are managed by the servers which provide the client with access.

• Data is normally stored centrally on a file server.• Centralised storage means it is easy to organise a

backup regime.• A server can hold all usernames/Passwords and

details of users access privileges.• Client-server networks are usually found in

businesses and organisations.

File Server

• A file server– Stores data files for all users on the network.– Holds information that lists the files each user

has access to.– Holds information about the access privileges

each user has and whether the user has both read and write access to a folder.

Print Server

• A print server– Receives print jobs from clients.– Queues the jobs.– Spools the jobs to disk while they are in the

queue.– Sends them, in turn, to the printer.

Web Server

• A web server– Enables HTML pages and other HTTP

documents to be shared and accessed by systems using a standard browser.

More Definitions

• A node is any device that is attached to a network, E.g. A workstation, a server, a printer.

• A Channel is a path over which data is transmitted between one computer and another.

Bus Topology

• All nodes are connected to a single channel.

• Used in LANs.• Workstations broadcast

to all nodes on the network.

• Each node recognises and accepts only its own message.

• Advantage– If a node breaks, the

network still operates.• Disadvantage

– A break in the channel disrupts all communications.

Ring Topology• Each node is

connected to a single channel, which is joined into a circle.

• Data travels in one direction only, each node passes the packet on until it reaches the destination.

• Advantages– High transfer rate.– Stable.

• Disadvantages– Cost.– Failure in one node can cause the

network to crash.

Star Topology

• All nodes are connected to 1 central device called a hub.

• All data is sent to the hub, which broadcasts it to all nodes.

• Advantages– A node or channel failure will

not disable network.

• Disadvantages– Cabling Cost.– Failure in central node will

crash the network.

Mesh Topology

• Multiple channels between nodes.

• Data can be sent through several routes.

• Advantages– A node or channel

failure will not disable network.

• Disadvantages– Cabling Cost.

Network Hardware

• A hub connects all the nodes of a network.– When they receive a signal from 1 node it is

broadcast to all nodes on the network.– Modern hubs amplify the signal before

broadcasting it across the network.– The more nodes on the network the poorer the

performance.

Network Hardware Cont.

• A switch operates like a ‘smart’ hub. A switch divides a network into separate segments.– More than one machine can speak at once and

only the intended recipient will receive the data.

– This cuts down on network traffic, improving performance.

Network Hardware Cont.• A router is a device which links two or

more networks.

• It’s function is to look at the destination of the packets and decide which route each packet should take.

• A router determines the next network point to which data on the network should be forwarded.

Network Hardware Cont.

• A Network Interface Card (NIC) is a small circuit board connected to the motherboard to allow the computer to communicate with a network.

• The NIC also provides a computer with a unique network address. This number is known as a Media Access Control address or MAC address.

Developing Trends

• Higher bandwidth– Bandwidth is a measure of the quantity of data

that may be carried through a channel at one time.

– The demands on network bandwidth are constantly increasing in order to:

• Run more complex software.• Transmit larger files.• Support video conferencing.

Developing Trends

• Wireless Communication– More and more devices have wireless

functions in order to access networks without a physical connection.

– Areas within the range of wireless base stations are known as hotspots.

– Problems can occur with interference, Hackers and Piggy Backing (unauthorised users on the network).

Advances in Computer Hardware

• Processors have become faster and one trend is to increase the number of processors on a single chip.

• Main memory capacity has tended to increase as the cost of RAM chips falls. This has allowed more complex Network operating systems to be developed.

Advances in Computer Hardware Cont.

• Backing storage capacity has increased as the cost of storage falls. Large capacity hard disk drives make it possible to store the data from many networks on a single file server.

• Data transfer rates are also increasing. A 10Mbps Ethernet is being replaced by 100Mbps which will then be replaces by 1000Mbps.This improved bandwidth allows larger files to be transferred in less time.

Advances in Computer Software

• Modern browsers have extended functionality with the addition of various plug-ins. These allow other types of data such as animated graphics and streamed video.

• A network operating system controls all the devices on a network so that resources can be shared efficiently. The network operating system also allows– Setting up user groups– Assigning access privileges– Implementing a security policy– Implementing a backup and recovery regime

Networks and the Law

• Networks are very powerful communication tools and used properly they support our businesses, schools, colleges and hospitals and enable us to communicate with people across the world.

• Unfortunately they are also used maliciously to damage computer systems, to steal and to cheat.

The Copyright & Patents Act• Most published material (including text, images, video, music,

software etc) is protected by the Copyright, Design and Patents Act 1988.

• Copyright may be infringed if, without the prior permission of the copyright owner, you– Copy a work (including scanning or storing electronically) – Issue copies to the public – Perform, show or play the work in public – Broadcast the work or include it in a cable programme – Make an adaptation of the work

• If you do any of these without permission, you are liable to be held personally responsible. Infringing the law may be a criminal offence.

The Computer Misuse Act

• This law makes it illegal to access a computer system without permission– Unauthorised access

– Unauthorised access with intent to commit an offence

– Unauthorised modification of data

– Persistently trying to guess or steel another's password

• Hacking and writing computer viruses are both made illegal by this act.

The Data Protection Act

• The data subject has the right to:– to inspect information held about them– have incorrect information changed– to apply for compensation if incorrect

information has causes distress.

What we should now know!• Comparison of LANs, WANs, Intranet and Internetwork in terms of transmission media,

bandwidth, geographical spread and functions.• Distinction between a mainframe with terminals and a network of computers • Descriptive comparison of peer-to-peer networks and client server networks • Description of the functions of file, print and web servers • Description of a node and a channel • Description of bus, star, ring and mesh topologies using the terms node and channel • Description of the consequences for each of the above topologies of node and channel

failure • Simple description of the functions and uses of a hub, switch and router • Identification of the need for a network interface card (NIC) • Description and explanation of the trends towards higher bandwidth and wireless

communications • Description of the following technical reasons for the increasingly widespread use of

networks: advances in computer hardware, including processors, main memory capacity, backing storage, data transfer rates improved network related software, including browsers and network operating systems

• Description of the misuse of networks for the following illegal purposes: breaching copyright, hacking and planting viruses

• Description of the application of the Computer Misuse Act, the Copyright Designs and Patents Act and the Data Protection Act to the misuse of networks