NetworksNetworks

Learning ObjectivesLearning ObjectivesExplain the client-server model of networked computers.Give examples of applications which use the client-server model.Describe what is meant by the World Wide Web (WWW) and the InternetExplain how hardware is used to support the Internet: networks, routers, gateways, servers.Explain how communication systems are used to support the Internet: The Public Service Telephone Network (PSTN), dedicated lines, cell phone networkExplain the benefits and drawbacks of using copper cable, fibre-optic cabling, radio waves, microwaves, satellites.Show understanding of bit streaming (both real-time and on-demand)Show understanding of the importance of bit rates/broadband speed on bit streaming.

Stand-alone machines

A computer: cannot communicate with and is not

connected to other computers. with all devices connected directly to it.

Disadvantages of stand-alone machines

Users cannot easily share information Every computer needs to be connected to a printer.

With these problems in mind, it was realised at an early stage that connecting these computers together would overcome many of these disadvantages.

Servers and Workstations / Terminals

Workstations / Terminals: A computer connected to other computers.

Servers: A computer that 'serves‘ and store files for the

workstations. They are often more powerful than a standard

computer because they need to store a vast amount of data. 

Communications software

Necessary to allow computers to communicate.

Computer Networks Advantages

A user can access their files from any workstation / terminal. Files and software can be shared by users.

Also some software can installed on all workstations from the server which makes installation quicker and easier.

Users can communicate with others on the network.Individual workstations do not need a printer, one high quality printer can now be shared by everyone, thus cutting costs. Networks provide security:

A user must have the correct Password and User ID in order to be able to access the information on the network.

Computer Networks Disadvantages

Networks can be expensive to set up: They often involve taking up floors and ceilings to lay

hundreds of metres of cables. The Server needs to be a powerful computer, which often means that it is expensive. Networks are vulnerable to security problems:

Hackers, disgruntled employees or even competitors might try to break into the system to read or damage crucial information.

Much effort is spent preventing unauthorised access to data and software.

Computer Networks Disadvantages

If the main Server breaks down, then the whole system becomes useless and no-one can carry on working. Because networks are often complicated, they need expensive expert staff to look after them. As the number of users increase on the network, the performance of the system can be affected and things start to slow down.

WorldWorld Wide Web / Wide Web / InternetInternetThe Internet is worldwide and intended to be accessed by The Internet is worldwide and intended to be accessed by anybody.anybody.A global network connecting millions of computers. A global network connecting millions of computers. The best “known” network.The best “known” network.More than 100 countries are linked into exchanges of data, More than 100 countries are linked into exchanges of data, news and opinions.news and opinions.The World Wide Web, or just "the Web," as ordinary people The World Wide Web, or just "the Web," as ordinary people call it, is a subset of the Internet. The Web consists of pages call it, is a subset of the Internet. The Web consists of pages that can be accessed using a Web browser.that can be accessed using a Web browser.The Internet is the actual network of networks where all the The Internet is the actual network of networks where all the information resides. information resides.

Things like Telnet, FTP, Internet gaming, Internet Relay Chat (IRC), Things like Telnet, FTP, Internet gaming, Internet Relay Chat (IRC), and e-mail are all part of the Internet, but are not part of the World and e-mail are all part of the Internet, but are not part of the World Wide Web. Wide Web.

http://techterms.com/definition/wwwhttp://techterms.com/definition/www

Advantages

Convenience:Convenience: accessible at home, work, or through a wireless accessible at home, work, or through a wireless

devicedevice

Easy to contact other people no matter where Easy to contact other people no matter where they are. they are. Access to other cultures Access to other cultures Access to a vast amount of information Access to a vast amount of information Can be used Night or Day - it never stops Can be used Night or Day - it never stops Can be used to learn (or teach) Can be used to learn (or teach) Makes it possible to Telework Makes it possible to Telework Possible to buy and sell things online Possible to buy and sell things online

Advantages

Can present their work more neatly

Pupils can share ideas

Less waste of paper

Disadvantages

Must have a home computerMust have a home computer

Transmission of virusesTransmission of viruses

Must have Internet / ModemMust have Internet / Modem

Must remember passwords / usernamesMust remember passwords / usernames

Pupils can copy off othersPupils can copy off others

DisadvantagesDisadvantages

Undesirable sites may be accessedUndesirable sites may be accessedHave to pay for internet accessHave to pay for internet accessMay receive unsolicited e-mails from May receive unsolicited e-mails from undesirable charactersundesirable charactersHealth reasonsHealth reasonsDemand on equipmentDemand on equipmentCan waste time exploring unreliable sitesCan waste time exploring unreliable sitesCan get distracted playing gamesCan get distracted playing games

Transmission Media Transmission Media (cables)(cables)

Presented in order of performancePresented in order of performance(increasing expense, (increasing expense, speed of communication, level of traffic that can be speed of communication, level of traffic that can be

managedmanaged, difficulty and usable length of installation and decreasing , difficulty and usable length of installation and decreasing susceptibility to interference)susceptibility to interference)

http://members.tripod.com/barhoush_2/cabling.htmhttp://fcit.usf.edu/network/chap4/chap4.htmhttp://www.ecst.csuchico.edu/~sim/547/Old547/notes/NOTE4.htm

CopperCopper - UTP & Shielded TP- UTP & Shielded TP

UUnshielded nshielded TTwisted wisted PPair (air (UTPUTP) ) Two conductors, enclosed in a Two conductors, enclosed in a

plastic sheath, twisted together. plastic sheath, twisted together.

Shielded Shielded TTwisted wisted PPairair Has a grounded screen around the Has a grounded screen around the

conductors to shield the cable from conductors to shield the cable from extraneous electromagnetic extraneous electromagnetic radiation. radiation.

Used in pre-existing telephone networks.Used in pre-existing telephone networks.

Changing current denotes different signals.Changing current denotes different signals.

CopperCopper - Coaxial cable - Coaxial cable

Baseband coaxial:Baseband coaxial: Single copper braid shield.Single copper braid shield.

Broadband coaxial:Broadband coaxial: Two shieldsTwo shields

1 - aluminium & 1 - copper.1 - aluminium & 1 - copper.

Central conductorPlastic insulators

Copper screen conductor

A central conductor enclosed in a plastic sheath A central conductor enclosed in a plastic sheath surrounded by a copper sheath which is surrounded by a copper sheath which is surrounded by a plastic coating.surrounded by a plastic coating.

Used in pre-existing telephone networks.Used in pre-existing telephone networks.

Changing current denotes different signals.Changing current denotes different signals.

Optical FiberOptical Fiber- Used as backbones (- Used as backbones (fast route)fast route) for LANs for LANs

or in WANsor in WANs

Contains many optical fibers:Contains many optical fibers: Glass or plastic fibers designed Glass or plastic fibers designed

to guide light along them.to guide light along them. Signals transmitted as light Signals transmitted as light

pulses so travel at the speed of pulses so travel at the speed of light with the highest bandwidth light with the highest bandwidth currently possible.currently possible.

Separate fibres can be used for Separate fibres can be used for separate signals. separate signals.

Wireless Communication

Radio signals: Satellite communications.

Microwave signals: Communication must be a straight line from sender to

receiver.

Wireless communication allows for mobile communication.

what-when-how.com/data-communications-and-networking/communication-media-data-communications-and-networking

RoutersRouters

LAN Router Public network

Router LAN

RoutersRouters

Connect different types of network Connect different types of network together.together. Stores logical IP addresses and can deal with Stores logical IP addresses and can deal with

complex networks where there is more than complex networks where there is more than one possible path to a destination by one possible path to a destination by calculating the optimum route at the time.calculating the optimum route at the time.

i.e. Directs packets across a packet switched i.e. Directs packets across a packet switched network.network.

Is software based as it uses its own operating Is software based as it uses its own operating system to make its decisions.system to make its decisions.

RoutersRouters

Directs messages down different routes Directs messages down different routes according to their desired destinations.according to their desired destinations. Use Use network addressesnetwork addresses and and addresses of other addresses of other

routersrouters to create a route between two networks so to create a route between two networks so must keep tables of addresses. must keep tables of addresses.

These tables are copied between routers using These tables are copied between routers using routing information protocol (RIP). routing information protocol (RIP).

Often used to connects LANs & WANs e.g. connect a Often used to connects LANs & WANs e.g. connect a LAN to the internet using one IP address.LAN to the internet using one IP address.

Operates at all layers up to the transport layer of OSI.Operates at all layers up to the transport layer of OSI.

Routing AlgorithmRouting Algorithm

1.1. Router receives a network level packet.Router receives a network level packet.

2.2. Network destination address is checked.Network destination address is checked.

3.3. Packet is sent to the appropriate Packet is sent to the appropriate network.network.

GatewayGateway

A gateway is a network point/router that acts as an A gateway is a network point/router that acts as an entrance to another network.entrance to another network.On the Internet, a node/router or stopping point can be On the Internet, a node/router or stopping point can be either a gateway node or a host (end-point) node/router. either a gateway node or a host (end-point) node/router. Both the computers of Internet users and the computers Both the computers of Internet users and the computers that serve pages to users are host nodes. that serve pages to users are host nodes. The computers that control traffic within your company's The computers that control traffic within your company's network or at your local Internet service provider (ISP) network or at your local Internet service provider (ISP) are gateway nodes/routers.are gateway nodes/routers.In the network for an enterprise, a computer server In the network for an enterprise, a computer server acting as a gateway node is often also acting as a proxy acting as a gateway node is often also acting as a proxy server and a firewall server.server and a firewall server.

http://en.wikipedia.org/wiki/Default_gatewayhttp://en.wikipedia.org/wiki/Default_gateway

Proxy ServerA proxy server is a computer setup to share a resource, usually an Internet connection.Other computers can request a web page via the proxy server. The proxy server will then get the page using its Internet connection, and pass it back to the computer who asked for it.Proxy servers are often used instead of router since additional software can be easily installed on the computer such as anti-virus, web filtering etc.

www.igcseict.info/theory/4/hware/index.html

Bit / Baud Rate

The speed at which a given amount of data can be transmitted. The number of bits that can be sent in one

second is known as the BIT RATE. The units used to measure the bit rate are BAUD.

1 baud = 1 bit per second.

Transmitting Pictures / Graphics

Pictures take up a lot of memory because each pixel must be defined.High resolution (quality) means more pixels and more colours.There is a limit to the amount of information that can be transmitted in a given time down the phone line.

Choice 1:Have as much detail as possible and accept that it will take a long time to transmit it.

Choice 2:Limit the resolution (quality) of the picture, meaning that there is less information to send so that the message will be sent more quickly.

Transmitting Text

Text files contain a relatively small amount of data (compared to pictures / graphics / video) because each character only takes one byte. Text files are not time sensitive.

They can still be read even if the bit / baud rate is slow and they get sent pretty quickly anyway due to their relatively small size.

Transmitting Video

Large amount of data which must be transmitted in a standard time frame. A video cannot be run (watched) without a

high bit / baud rate.

Importance of Bit / Baud Rate

More important the more data there is. Due to the increasing time required for transfer.

Different volumes per second mean that different transfer rates are appropriate.

Videos demand a high bit / baud rate Contain a large amount of data.Must be transmitted in a standard time frame.

Pictures take a long time without a high bit / baud rate.

Large amount of data because each pixel must be defined. Text doesn’t need a high bit / baud rate.

Small amount of data.Not time sensitive.

Bit Streaming

Multimedia that is constantly received by and presented to an end-user while being delivered by a provider.

Video on demand:Systems which allow users to select and watch/listen to video or audio content when they choose to, rather than having to watch at a specific broadcast time.

https://en.wikipedia.org/wiki/Video_on_demand Real-time:

Refers to content delivered live over the Internet.Requires a form of source media (e.g. a video camera, an audio interface, screen capture software) and an encoder to digitize the content, a media publisher, and a content delivery network to distribute and deliver the content.

https://en.wikipedia.org/wiki/Streaming_media

PlenaryPlenary

What are the advantages and disadvantages of using the Internet?

Advantages

Allows communication.Allows communication.

Pupils can share ideas.Pupils can share ideas.

Large amounts of educational material.Large amounts of educational material.

Allows students to access information to Allows students to access information to help with studies and to enjoy their help with studies and to enjoy their learning.learning.

Allows student to learn at own speed / at Allows student to learn at own speed / at own times.own times.

Disadvantages

Many sites do not give accurate information.Many sites do not give accurate information.

Many sites give access to inappropriate material Many sites give access to inappropriate material (downloading music / ordering drugs / watching (downloading music / ordering drugs / watching pornography).pornography).

Health and Safety problems.Health and Safety problems.

Sites available to buy coursework / helps to Sites available to buy coursework / helps to cheat in examinations.cheat in examinations.

May allow hacker into your system / viruses May allow hacker into your system / viruses prevalent.prevalent.

DisadvantagesDisadvantages

Undesirable sites may be accessedUndesirable sites may be accessedHave to pay for internet accessHave to pay for internet accessMay receive unsolicited e-mails from May receive unsolicited e-mails from undesirable charactersundesirable charactersHealth reasonsHealth reasonsDemand on equipmentDemand on equipmentCan waste time exploring unreliable sitesCan waste time exploring unreliable sitesCan get distracted playing gamesCan get distracted playing games

PlenaryPlenary

Explain the part played in network Explain the part played in network systems by:systems by:

SwitchesSwitches RoutersRouters BridgesBridges ModemsModems

PlenaryPlenary

SwitchesSwitches A device that allows many terminals all to use the A device that allows many terminals all to use the

same communications line at different times.same communications line at different times.

RoutersRouters Connects different types of network together.Connects different types of network together. Software at a node (on the network).Software at a node (on the network). Which directs messages down different routes.Which directs messages down different routes. According to their desired destination.According to their desired destination.

PlenaryPlenary

BridgesBridges Links two LANs (which may or may not be similar).Links two LANs (which may or may not be similar). Uses address information in packets.Uses address information in packets. Has the ability to learn the layouts of the networks.Has the ability to learn the layouts of the networks. Can control access from one part of the network to Can control access from one part of the network to

the other.the other.

ModemsModems Necessary if communication link is analogue.Necessary if communication link is analogue. Converts digital signals to analogue for Converts digital signals to analogue for

transmission.transmission.

Plenary

Explain the importance of bit rates to communication.

Importance of Bit / Baud Rate

More important the more data there is. Due to the increasing time required for transfer.

Different volumes per second mean that different transfer rates are appropriate.

Videos demand a high bit / baud rate Contain a large amount of data.Must be transmitted in a standard time frame.

Pictures take a long time without a high bit / baud rate.

Large amount of data because each pixel must be defined. Text doesn’t need a high bit / baud rate.

Small amount of data.Not time sensitive.