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This topic considers the various ways in which computers can be connected to each other to communicate, share data and peripherals.

Four categories of network are covered in the course:

1. LAN

3. Internet

4. Intranet

2. WAN

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a. Transmission media

c. Geographical spread

d. Functions

b. Bandwidth

In looking at the four categories of networks we will compare them using the following four characteristics:

Refers to the type of cabling or wireless method used to transfer data.

Relates to the speed at which data can be transferred throughout the network.

Looks at the size of the area which the network covers.

Considers what tasks the network can carry out for the users.

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1. LAN

2. WAN

3. Internet

4. Intranet

a. Transmission media

c. Geographical spread

d. Functions

b. Bandwidth

Fibre-optic cable, Unshielded twisted pair(UTP) cable, co-axial cable (as used in a tv aerial.)

This depends on the cabling and hardware used. UTP cable allows data transfer at 10 – 100 Mbps

Physical cabling is laid to connect the network. Usually one building, school, office, factory. Typically up to about two km.

Peripheral sharing, electronic mail, data sharing.

http://fcit.usf.edu/network

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1. LAN

2. WAN

3. Internet

4. Intranet

a. Transmission media

c. Geographical spread

d. Functions

b. Bandwidth

Telecommunications systems covering large areas.

Slower than LAN. Depends on the link used. Modem dial-up up to 56 Kbps. ADSL up to 9 Mbps, dedicated line up to 45 Mbps.

WANs can cover any size of area. They use telecommunications which covers most of the earth.

Electronic mail, data sharing, conferencing.

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1. LAN

2. WAN

3. Internet

4. Intranet

a. Transmission media

c. Geographical spread

d. Functions

b. Bandwidth

Telecommunications systems covering large areas.

Same as WAN. Depends on the link used. Modem dial-up up to 56 Kbps. ADSL up to 9 Mbps, dedicated line up to 45 Mbps.

The Internet can cover any size of area. They use telecommunications which covers most of the earth.

Electronic mail, information sharing using WWW, File sharing using FTP.

An internet is a network of networks

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1. LAN

2. WAN

3. Internet

4. Intranet

a. Transmission media

c. Geographical spread

d. Functions

b. Bandwidth

Telecommunications systems covering large areas.

Slower than LAN. Depends on the link used. Modem dial-up up to 56 Kbps. ADSL up to 9 Mbps, dedicated line up to 45 Mbps.

Intranet can cover any size of area using telecommunications links which cover most of the earth. The Council has its own intranet.

An intranet is like the internet but confined to one organisation.

Electronic mail, information sharing using WWW, File sharing using FTP.

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A mainframe is a very large computer which provides processing power and backing storage facilities to users working at terminals.

A terminal is a monitor and keyboard with little or no processing power and no storage facility.

Mainframes were popular for large scale computing ventures but many have been replaced by newer client server networks.

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Mainframes offer the following facilities:

High capacity input/output. Can access and store data for thousands of users simultaneously

Powerful processing capability. Can process data for thousands of users simultaneously

Centralised storage, processing and management of large amounts of data.

Comprehensive backup, recovery and security for the system

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Unlike a mainframe, a network is a collection of independent computers connected together.

Each of the computers has its own processing power and backing storage capability and is capable of functioning as a standalone computer.

In the Higher course we will look at two types of network:

1. Peer-to-peer network.

2. Client Server network.

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In a peer-to-peer network all the computers have equal status.

Each computer can choose to share its resources with the other computers. Resources include printers, backing storage devices, data files.

There is no centralised backing storage as each computer stores its own data and applications. A system for backups is therefore difficult to implement.

Security is difficult to maintain as resources, user names and passwords are not centrally managed.

Most home networks are peer to peer.

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In a Client Server network some computers are clients. People use these to access the network.

Backing storage is centralised and all user files are stored on a file server. It is easy to make backups on the file server.

The server holds a database of all user names, passwords and access rights. Security is easy to maintain as it is centrally managed.

The school network is an example of a client server network.

A server is a computer which controls a resource that is made available to clients on the network. Resources might include applications, data files, printers, email or internet access.

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• Backing storage is centralised and all user files are stored on a file server. It is easy to make backups on the file server.

• The server holds a database of all user names, passwords and access rights. Security is easy to maintain as it is centrally managed. Can allow different levels of access for different users

• Reports about users and computer use can be easily generated.

Advantages of a client-server network

• Easy to update software as it is done centrally

• Easy to manage and control use of resources such as printers, internet.

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File ServerStores users’ data files.Controls file access. Each user has access to certain files.

Controls the type of access. e.g. read only, write, create

Print Server

Handles all printing requests from clients.Queues jobs, spools them to disk and sends to printer when printer is ready.

1. File Server

2. Print Server

3. Web Server

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Web Server

Requests for internet access including Web pages, email and file sharing are dealt with by this server.

1. File Server

2. Print Server

3. Web Server

Web Server advantages

• Pages can be held locally(cached) which allows faster access to pages.

• Use of the internet can be monitored more easily when all internet access goes through the web server.

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The topology of a network refers to the shape of the network, how the computers are physically connected together.

A node is any device which is attached to the network.

A channel is the way in which data is transferred from one node to another.

e.g. a computer, printer, server, router.

This could a cable or some form of wireless technology.

Four topologies are covered in the Higher Course.

node

channel

Network topology diagrams must always be labelled with the words node and channel

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1. Bus

2. Star

3. Ring

4. Mesh

Used in LANS.

All nodes are connected to a single channel.

A communication from one node is seen by all the other nodes.

Each node will recognise and accept communications which are addressed to it.

or

nodechannel

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1. Bus

2. Star

3. Ring

4. Mesh

Node Failure

Channel Failure

There is typically a mechanism to bypass a failed node so failure of one node will only affect that node. Rest of network will still function.

A channel failure will cause the whole network to fail.

ornodechannel

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1. Bus

2. Star

3. Ring

4. Mesh

Used in LANS.

Each node has its own channel to the central node.

The whole network depends on the proper functioning of the central node.

Cabling cost is high because each node has its own channel but it is easy to extend the network.

nodechannel

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1. Bus

2. Star

3. Ring

4. Mesh

Node Failure

Channel Failure

A failure of one node will only affect that node. Failure of the central node will disable the entire network.

A channel failure will only affect the outer node on that channel.

nodechannel

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1. Bus

2. Star

3. Ring

4. Mesh

Used in LANS.

Channels and nodes form a ring.

Only one node can transmit at a time and data passes between nodes until it reaches its destination.The network has to be disrupted when a new node is added. Designing and extending the network is more difficult than with a star network.

nodechannel

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1. Bus

2. Star

3. Ring

4. Mesh

Node Failure

Channel Failure

A channel failure will disable the entire network.

nodechannel

There is typically a mechanism to bypass a failed node so a failure of one node will only affect that node.

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1. Bus

2. Star

3. Ring

4. Mesh

Used in WANS. e.g. telephone grid.

There are alternative channels between nodes.

Several nodes can transmit at a time and data can be redirected when some channels are busy.

The extra cabling makes this an expensive type of network to set up but it is very robust.

nodechannel

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1. Bus

2. Star

3. Ring

4. Mesh

Node Failure

Channel Failure

The failure of one node will only affect that node.

A channel failure will have no effect as alternative channels are available. It may, however, slow down traffic on the network.

nodechannel

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Some nodes on a network are devices which are there to manage the flow of data.

When data is sent it includes a destination address.

Each node on the network has its own address to uniquely identify it.

1. Hub

2. Switch

3. Router

Three common devices used for managing the flow of data are:

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Stackable hubs with 8, 16 or 24 ports can be linked to form large LANS.

Nodes are connected to a hub via channels.

When data is received from a node it is broadcast to all the other ports.

It may also amplify the signal if long distances are involved.

This is inefficient as the data is intended for only one of the other nodes.

1. Hub

2. Switch

3. Router

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A switch is sometimes known as an intelligent hub.

When data is received from a node it is examined and then sent directly to the destination known.

Switches are more complex than hubs and are therefore more expensive.

This is more efficient than a hub as the data goes directly to the destination node.

1. Hub

2. Switch

3. Router

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Faster NIC(Network Interface Cards) could also improve technical performance.

How can you improve the technical performance of a network which uses a hub?

A Switch would be more efficient than a Hub in that it doesn’t broadcast data to all nodes on the network

Higher specification cabling could improve technical performance.

1. Hub

2. Switch

3. Router

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They connect LANS to telecommunications lines and the Internet.

Routers connect different networks together.

They control and manage the flow of data over the different networks.

They cope with the differences in topologies and transmission media.

They connect smaller networks into larger internetworks.

1. Hub

2. Switch

3. Router

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Each device on a network requires an interface to allow it to connect.

A Network interface card (NIC) is usually slotted into the motherboard of the device.

Wireless interface cards can also be used. These can use USB or PCMCIA cards to allow devices to connect.

The NIC converts the data to and from a format that can be transmitted over the network .

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Higher Bandwidth

Technology is improving rapidly and improvements in bandwidth increase the rate of data transfer.

Higher bandwidth allows the possibility of transferring video, graphics and audio and will allow live streaming of data.

• Play network multi-user games with high resolution graphics.

• Video conferencing.

• Transmit large data files.

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Wireless Communications

Wireless communication increases flexibility of use and is becoming more popular for home, office and public spaces.

• No wiring required and ability to move around.

• Can be affected by electrical interference.

• Easy to hack into unless firewall security is enabled.

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There are many technical reasons for the increasingly widespread use of networks. These include:

• Advances in computer hardware.

• Network interface cards (NIC) are now built into most computers

• Wireless technology makes it easier to work on a network.

• Higher bandwidth and faster connection speeds make networking more attractive

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• Improvements in network related software.

There is a standard protocol for communication – (TCP/IP)

Networking software is now built into common operating systems e.g. Windows Vista, Linux and Windows XP

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The use of networks which can be local, national or even international poses legal problems for governments.

Three Acts in particular are relevant for possible network misuse.

Computer Misuse ActThis Act makes it illegal to breach network security for any reason.

“Hackers” can be fined or imprisoned for gaining access and looking at or altering data and also for introducing viruses.

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Copyright, Designs & Patents Act

This Act makes it illegal to make unauthorised copies of material.

Offenders can be fined or imprisoned for being involved in this activity and FAST(The Federation Against Software Theft) have had many companies and individuals prosecuted.

It is very easy on a network to transfer audio, video and text at high speed. This has led to a huge increase in the unauthorised pirating of music, films and books.

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Data Protection Act(1998)

The Act gives individuals(Data Subjects) rights to:

• gain access to their data.

• seek compensation if inaccurate information causes damage.

• "opt-out" of having their data used for direct marketing.

• "opt-out" of fully automated decision-making about them.

The principles of this Act also apply to network use.

http://www.informationcommissioner.gov.uk/

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Data Protection Act(1998)

Organisations processing personal data ("controllers") must comply with the data protection principles. These require data to be:

• fairly and lawfully processed.

• processed for limited purposes.

• adequate, relevant and not excessive.

• Accurate.

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Data Protection Act(1998)

• not kept longer than necessary.

• processed in accordance with individuals' rights.

• kept secure.

• not transferred to non-EEA (European Economic Area) countries without adequate protection.