Networks

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• Describe the characteristics and relative advantages of network and stand-alone environments.

• Describe the difference between a Local Area Network (LAN) and a Wide Area Network (WAN).

• Describe the required elements of network environments including hardware, software, communications and topology.      

Links

• Local Area Networks & Wide Area Networks.• Software.• Topology.• Peer to Peer, Client Server.• Hardware.• Transmission Media.• Ethernet & Token Ring.

A Network System

• There are three parts to a network system:• 1. a sender of information;• 2. a communications link;• 3. a receiver of information.

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Types

• There are two types of computer network: • 1. a wide area network (WAN) – computers are

linked city to city, or country to country.• 2. a local area network (LAN) – computers are

linked from office to office, or building to building.• 3. a metropolitan area network (MAN) – not a

WAN but may link computers in different parts of a city, not a LAN but may link computers from building to building.

Networked Computers in a Call-Centre

Typical NetworkConfiguration

Local Area Network

• A local area network (LAN) is normally used for sharing of resources such as a printer or files of data.

• LAN’s are usually confined to a single site, such as a school, but may extend to groups of buildings stretched across a city, such as a university campus.

• Each computer (workstation) on the network is linked by cable to a central server using one of a number of systems.

Wide Area Network

• A wide area network is normally used to link groups of computers across long distances.

• A multinational company in New York will have its own LAN, but to link with its Japanese offices LAN, it will need to make use of a WAN.

• The WAN will be made up of telephone lines, radio and satellite links, all run by the local public providers. These will have their own charges.

• Alternatively the company may pay for a permanent link between offices, known as a leased line. The company pays a fixed rate for the permanently open connection.

Advantages of Networks

1. A common pool of data is shared among all the users, without duplication.

– Consider a catalogue telephone sales dept.– What is the system for entering sales into a

database from 50 operatives all using connected workstations?

– What is the system for entering sales into a database from 50 operatives all using stand alone PC’s?

2. Sharing of hardware resources such as printers, scanners, fax etc.

- Consider a school where many students need to print off their coursework.

- How would a whole class print off all their work in a single lesson from 24 networked workstations?

- How would a whole class print off all their work in a single lesson if only one PC is connected to the printer?

- Would an option of connecting a printer to each computer be feasible?

3. Software with a licence for x number of workstations on a network is available cheaper than single use licences. Most programs can be downloaded onto workstations from the server, saving time and money.

4. The back-up of data is done centrally by a network manager, daily or weekly, and copies kept for some time.- What are the consequences if left to individuals?

5. Better communication is achieved between users, the system may be linked to the Internet. - What is a company Intranet? - How would users communicate to each other?

6. Improved security from theft, destruction, spying.

- Where are the data files kept on a networked system?

- Where are the data files kept on a PC?

- How can some networked workstations operate without a hard drive?

7. As programs are kept on the server, upgrading and maintenance becomes one operation for all workstations that access these programs.

Advantages of Stand Alone PC’s

1. The setup of a stand alone system is cheaper, there are no special software, connections and cabling required.

2. The IT manager requires less knowledge than a network administrator.

3. Security problems are isolated such as a virus introduced by an infected floppy disk.

4. The system is not dependant on the running and maintenance of a central server, therefore is less expensive to run.

Network Software

• Special software is required to run the network. • Microsoft Windows NT Server 4.0 is a multipurpose

server operating system. A multipurpose operating system integrates a variety of network services. The services it provides are designed to address customer requirements and are managed in a single way.

• http://www.microsoft.com/ntserver/ProductInfo/features/Features.asp

• X11 for Mac OS X is another server operating system based on UNIX for Apple Macs.

• http://www.apple.com/macosx/newfeatures/

Topology• Topology is the way devices are linked in

a certain design either physically and / or logically.

• There are different topologies:– Bus;– Ring; – Star;– Mesh.

• There are different types of network:– Peer to Peer;– Client Server.

Bus Network

Terminal Central Cable

Workstations, File Server, Printer.

• Data is sent from the sender to all other devices (nodes), this may be the server or a workstation.• There is no computer in control but there may be a server that stores the data files.• Advantages: simple, reliable, cheap, short cabling.• Disadvantage: slow when busy or a large network, as only one computer at a time can transmit data.

Bus Network

What would happen to the network if a workstation breaks down?

X

Ring Network

• Data is sent from the sender, it goes around the ring being read by each computer, if it is not for that one, it gets sent to the next, until it reaches its destination.

• Data has to wait its turn before sending, special software (token) writes an address for sender and destination.

Workstationswith In and Out Connections.File server and Printer.

Token Ring

Ring NetworkWhat would happen to the network if a workstation breaks down? X

Advantage: all nodes can access the Token equally, high speed.

Disadvantage: all on one path, therefore maintenance is highfor faults and failures.

Star Network

Data is controlled bya central server, messages sent and received are read by the controller.Each workstation hasIts own dedicated link.

Advantages: fast withhigh volumes of data, extra nodes added withoutany disconnections.

Central Controller Node

Workstations

Star NetworkWhat would happen to the network if a workstation breaks down? XDisadvantages: if theCentral controller fails thewhole system is down, large amounts of cableare required, so it may get expensive.

Mesh Network

Data sent from node to node goes by a direct link.Possible to leave out some paths as there aremany alternative routes.

Advantages: very fast, and fault tolerant.Disadvantages: very largeamounts of cabling, resultingIn higher maintenance costs.

Mesh NetworkWhat would happen to the network if a workstation breaks down?

X

Peer to Peer Network

• File storage and printing facilities are not accessed from the central server, but from any of the computers on the network.

• Any workstation can use the others facilities, i.e. hard disk, CD drive, printer, etc.

• These networks are easy to install and run, but become slow if being used for a large network of over 20 stations.

• These networks need a network interface card (nic), cable, and network operating system software to work.

Peer to Peer

• Advantages: – ordinary equipment only, – no need for an administrator, – easy to get started,– cheap to connect,– user sets up their own defaults, more

personal,– user controls their own resources,– no costly maintenance and repair, no reliance

on one main computer.

Peer to Peer

• Disadvantages:– no central organisation of data, bit are kept on

different hard disks, archiving haphazard,– back-ups are done individually each of the

users, not done in one go centrally,– users have to run their own computers in line

with company policy, need more skills,– security may be more easily compromised

without a user name and password system.

Peer to Peer

How does thelaptop user printout her work?

Client Server Network

• The server is a powerful computer containing the files, the programs, the maintenance, the printer and other resources.

• The server contains high processing power (some have several CPU’s), and high storage capacity, with back up facilities.

• A hub or switch is needed to control the flow of traffic in the network so that signals do not interfere with each other.

• The software is a network operating system capable of Internet gateway facilities.

Data Control

• Files are stored on the central server, where they are available for everyone with access to use.

• Some parts of the file are kept on the server, other parts are available for the client, these are the parts that can be read, written, amended, deleted etc.

• The updated file is then returned to the server when saved.

• The amount of data that is sent and returned is kept to a minimum allowing other users file transfer time.

The Clients

• The client is the workstation being used to access the data held on the server.

• All the client computers work independently from each other, so any that are faulty or taken off the network for maintenance do not affect the performance of the system.

Advantages

• Advantages over peer to peer:– speed of transfer as only part of the files need

be sent by dedicated servers,– all users work on the same piece of data,– the running and maintenance is done by a

specialist, users don’t need this knowledge,– security is centralised through user access

and passwords, and files are stored centrally,– back-up of files are done for all files regularly

and centrally.

Disadvantages

• Disadvantages:– Entirely dependant on the server, the system

is down if the server has a fault.– a more costly system to run, with expensive

equipment, needing a specialist network administrator,

– software is more expensive as it is dedicated to network use.

Client Server

How many deviceshave access to theprinter?