Wireless LANS

Wireless LANSWireless LANS

Justin ChampionJustin ChampionRoom C208 - Tel: 3273Room C208 - Tel: 3273

www.staffs.ac.uk/personal/engineering_and_technology/jjc1www.staffs.ac.uk/personal/engineering_and_technology/jjc1


ContentsContents What is a LANWhat is a LAN Types of wireless LANTypes of wireless LAN

AdHocAdHoc InfrastructuredInfrastructured

Infrared CommunicationsInfrared Communications Uses of these technologiesUses of these technologies


What is a LANWhat is a LAN There are two main types of network There are two main types of network

infrastructuresinfrastructures Local Area Network (LAN)Local Area Network (LAN) Wide Area Network (WAN)Wide Area Network (WAN)

The classification for these types of networks is The classification for these types of networks is the distance that the data has to travelthe distance that the data has to travel There is no exact formula to classify when a LAN There is no exact formula to classify when a LAN

becomes a WAN in a wired network!becomes a WAN in a wired network! Consider Staffordshire university is the email server part of a Consider Staffordshire university is the email server part of a

WAN as it is located in Stoke?WAN as it is located in Stoke? Or a LAN as it is all one networkOr a LAN as it is all one network


LANLAN The network in this campus is a example of a The network in this campus is a example of a

LANLAN All machines are attached and located close to All machines are attached and located close to

each othereach other Distance in network terms is classified by the number Distance in network terms is classified by the number

of hops travelled between one device and anotherof hops travelled between one device and another Hops are the stages that information has to travel Hops are the stages that information has to travel

through to get to the destination.through to get to the destination.


LANLAN Within a wireless network this is easierWithin a wireless network this is easier There is a physical limit to any wireless LAN There is a physical limit to any wireless LAN

technology.technology. Bluetooth – 10 MetresBluetooth – 10 Metres Infrared – 1 metreInfrared – 1 metre

After these physical limitsAfter these physical limits The Bit Error Rate (BER) becomes too high for realistic The Bit Error Rate (BER) becomes too high for realistic

communications to take placecommunications to take place The BER indicates what percentage of bits sent arrive at the The BER indicates what percentage of bits sent arrive at the

destination in errordestination in error


Types of networksTypes of networks In wired networks there is always an In wired networks there is always an

infrastructureinfrastructure Even if two people bring together laptops for a game, Even if two people bring together laptops for a game,

there will be a cable and a device to repeat the signalthere will be a cable and a device to repeat the signal A Hub, Router or Switch on EthernetA Hub, Router or Switch on Ethernet

WirelessWireless This may not be the caseThis may not be the case The devices may only be able to communicate for a The devices may only be able to communicate for a

few seconds and then they are out of rangefew seconds and then they are out of range People may come together for a meeting and then People may come together for a meeting and then

move away againmove away again


Types of networksTypes of networks AD-HOCAD-HOC

No pre planning of the network takes placeNo pre planning of the network takes place Communications may happen for hours or secondsCommunications may happen for hours or seconds

Using the Nokia N-Game with friends is an example of thisUsing the Nokia N-Game with friends is an example of this Business men in a meeting exchanging dataBusiness men in a meeting exchanging data

Difficulty in routing data to these devicesDifficulty in routing data to these devices

InfrastructuredInfrastructured The network has been plannedThe network has been planned The structure would not changeThe structure would not change

A office would be a good example of thisA office would be a good example of this


Ad-HocAd-Hoc These networks work as the devices come within the These networks work as the devices come within the

transmission distance of each othertransmission distance of each other When these devices can be used to extend a networkWhen these devices can be used to extend a network

In this diagram device B can not reach the printerIn this diagram device B can not reach the printer

Device B

Device A

Printer

Wireless LANSWireless LANS Ad-HocAd-Hoc

One device can be used to reach the device you actually One device can be used to reach the device you actually requirerequire The packet is sent from device B to A and then to the printerThe packet is sent from device B to A and then to the printer

Device B

Device A

Printer

Wireless LANSWireless LANS Ad-HocAd-Hoc

These networks are an active research areaThese networks are an active research area The technology works nowThe technology works now The difficulty is working out a route through the networkThe difficulty is working out a route through the network

The route change all of the timeThe route change all of the time Each time a packet is sent to sort out a route this takes battery Each time a packet is sent to sort out a route this takes battery

power on all devicespower on all devices With enough devices nothing but routing information will be sentWith enough devices nothing but routing information will be sent

Ad-Hoc protocolAd-Hoc protocol Mobile Ad-hoc Networks (MANET)Mobile Ad-hoc Networks (MANET)

This group is standardising the IP routing protocolsThis group is standardising the IP routing protocols (www.ietf.org/html.charters/manet-charter.html)(www.ietf.org/html.charters/manet-charter.html)

Wireless LANSWireless LANS InfrastructureInfrastructure

This would be used to supplement the current This would be used to supplement the current networknetwork This allows for laptopsThis allows for laptops Reduces the amount of cablesReduces the amount of cables

This reduces infrastructure costsThis reduces infrastructure costs Allows workers to operate where they want in the buildingAllows workers to operate where they want in the building

Usually combined with wired infrastructureUsually combined with wired infrastructure Examples would be central high power printersExamples would be central high power printers

Planning is requiredPlanning is required Remember that a radio signal from one device is just Remember that a radio signal from one device is just

interfering noise to another deviceinterfering noise to another device The more interfering devices the less successful communications The more interfering devices the less successful communications

that can take placethat can take place

Wireless LANSWireless LANS InfrastructureInfrastructure

Planning is required to minimise the amount of Planning is required to minimise the amount of interferenceinterference This can be done by increasing the distance between This can be done by increasing the distance between

high users of a systemhigh users of a system Different rooms for the devicesDifferent rooms for the devices

Some building materials will dampen the signalSome building materials will dampen the signal Staffordshire University Octagon is an example of this kind Staffordshire University Octagon is an example of this kind

buildingbuilding


The TechnologiesThe Technologies


Before we start on this course clarification of a Before we start on this course clarification of a widely used term the “Packet”widely used term the “Packet” All data which is transported on a network (wired All data which is transported on a network (wired

or wireless) is broken into smaller partsor wireless) is broken into smaller parts These parts are referred to as packetsThese parts are referred to as packets

Each packet is then sent to the recipientEach packet is then sent to the recipient The packets are then reassembled into the original dataThe packets are then reassembled into the original data Packets usually consist ofPackets usually consist of

Control informationControl information The data which is being transportedThe data which is being transported A checksum to ensure the packet is not corruptedA checksum to ensure the packet is not corrupted


InfraredInfrared Large installation baseLarge installation base

Most devices install these portsMost devices install these ports PhonesPhones LaptopsLaptops PrintersPrinters

Not widely used!Not widely used! Question becomes why?Question becomes why?

Standards defined ByStandards defined By Infrared Data Association (IRDA)Infrared Data Association (IRDA)

www.irda.orgwww.irda.org


Infrared – Operates by line of sightInfrared – Operates by line of sight


InfraredInfrared The data is encoded into pulses of Infrared (IR) lightThe data is encoded into pulses of Infrared (IR) light

Your television remote control works in the same mannerYour television remote control works in the same manner Technology is suited to Technology is suited to

Short distances with all devices within a roomShort distances with all devices within a room It is purposely designed to operate at about 1 meterIt is purposely designed to operate at about 1 meter

This give IR security built in in respect that no one can ‘listen’ to that This give IR security built in in respect that no one can ‘listen’ to that conversionconversion

Data RatesData Rates Although IR is considered to be a slow technology it is developingAlthough IR is considered to be a slow technology it is developing

Serial IR Serial IR – – 115.2 Kbps115.2 Kbps Medium IDMedium ID – – 1.152 Mbps1.152 Mbps

Rarely UsedRarely Used Fast IR Fast IR – – 4 Mbps4 Mbps

Latest phones, cameras, etc support this standardLatest phones, cameras, etc support this standard Very Fast IR Very Fast IR – – 16 Mbps16 Mbps

Microsoft Windows XP supported onlyMicrosoft Windows XP supported only


InfraredInfrared Advantage of the line of sight problem is that the Advantage of the line of sight problem is that the

communications are not sharedcommunications are not shared The devices need to be within a 30The devices need to be within a 3000 arc of each other arc of each other

Once the receiver and sender have agreed a Once the receiver and sender have agreed a transmission speed very little can interfere with thistransmission speed very little can interfere with this

This reduces the overhead on communicationsThis reduces the overhead on communications Collisions do not need detectingCollisions do not need detecting Secure communications layer does not need addingSecure communications layer does not need adding


What is a Stack?What is a Stack? The term stack refers to the The term stack refers to the Open System Open System

Interconnection (Interconnection (OSI) StackOSI) Stack This is a network standard that defines what communications This is a network standard that defines what communications

should take at which stageshould take at which stage There are 7 layers to the stack as shown belowThere are 7 layers to the stack as shown below Each layer carries out a specific taskEach layer carries out a specific task Each layer can only communicate to the layer above or belowEach layer can only communicate to the layer above or below All other network protocols map to this stackAll other network protocols map to this stack

Not all layers are used with every protocolNot all layers are used with every protocol

PhysicalData LinkNetwork

TransportSession

PresentationApplication


Communication between devices using the stackCommunication between devices using the stack Packet of information going from device 1 to device 2Packet of information going from device 1 to device 2


TransportSession



TransportSession


Device 1 Device 2Logically


Infrared Communication StackInfrared Communication Stack Only the layer above and below can communicate with Only the layer above and below can communicate with

a point in the stacka point in the stack

IAS

irLMP

irLAP

Physical

TinyTP

irLAN OBEX irCOMM

Required

Optional


PhysicalPhysical Defines encoding/decoding of data and transmission of the Defines encoding/decoding of data and transmission of the

signalsignal IRLAPIRLAP

Link Access ProtocolLink Access Protocol Responsible for ensuring a reliable transport of dataResponsible for ensuring a reliable transport of data

IRLMPIRLMP Link Management ProtocolLink Management Protocol

Multiplexes services and application together to use the one Multiplexes services and application together to use the one connection for transportconnection for transport

IASIAS Information Access ServiceInformation Access Service

Allows knowledge of the capabilities/services of the deviceAllows knowledge of the capabilities/services of the device

Wireless LANSWireless LANS Optional uses of IROptional uses of IR

TinyTPTinyTP This is a version of transport protocol designed specifically for IRThis is a version of transport protocol designed specifically for IR

Flow control is offered ensuring that device buffers do not overflowFlow control is offered ensuring that device buffers do not overflow Maximum packet sizes are agreed by devicesMaximum packet sizes are agreed by devices Large packets can be broken into smaller partsLarge packets can be broken into smaller parts

irOBEXirOBEX Object exchange protocolObject exchange protocol

Allows transfer of files easily between devicesAllows transfer of files easily between devices

irCOMMirCOMM Allows emulation of serial and parallel portsAllows emulation of serial and parallel ports

The applications do not need to know that they are using IRThe applications do not need to know that they are using IR Legacy applications will work with this a printer is an example Legacy applications will work with this a printer is an example

irLANirLAN Allows LAN access for the devicesAllows LAN access for the devices

Mainly used to allow LAN access through a device which is already connected Mainly used to allow LAN access through a device which is already connected to the networkto the network

Wireless LANSWireless LANS So why is not widely usedSo why is not widely used

Although newer versions of the technology are fast Although newer versions of the technology are fast the image is still for a slow technologythe image is still for a slow technology

Sun lightSun light The sun gives off IR and as such in bright light this will effect The sun gives off IR and as such in bright light this will effect

the operationthe operation Makes operation in the open awkwardMakes operation in the open awkward

Positioning Positioning The devices need to be in line of sight, which means that The devices need to be in line of sight, which means that

they need moving from there normal positionthey need moving from there normal position The distance between the devices can effect the rate of The distance between the devices can effect the rate of

transfertransfer Too close can be as bad as too far!Too close can be as bad as too far!


SummarySummary What is a LANWhat is a LAN OSI StackOSI Stack PacketPacket Infrared communicationsInfrared communications

Documents

Wireless LANS