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Wireless LANS. Justin Champion Room C208 - Tel: 3273 www.staffs.ac.uk/personal/engineering_and_technology/jjc1. Wireless LANS. Contents What is a LAN Types of wireless LAN AdHoc Infrastructured Infrared Communications Uses of these technologies. Wireless LANS. What is a LAN

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Wireless lans

Wireless LANS

Justin Champion

Room C208 - Tel: 3273


Wireless lans1
Wireless LANS

  • Contents

    • What is a LAN

    • Types of wireless LAN

      • AdHoc

      • Infrastructured

    • Infrared Communications

    • Uses of these technologies

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Wireless LANS

  • What is a LAN

    • There are two main types of network infrastructures

      • Local Area Network (LAN)

      • Wide Area Network (WAN)

    • The classification for these types of networks is the distance that the data has to travel

      • There is no exact formula to classify when a LAN becomes a WAN in a wired network!

        • Consider Staffordshire university is the email server part of a WAN as it is located in Stoke?

          • Or a LAN as it is all one network

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Wireless LANS

  • LAN

    • The network in this campus is a example of a LAN

    • All machines are attached and located close to each other

      • Distance in network terms is classified by the number of hops travelled between one device and another

      • Hops are the stages that information has to travel through to get to the destination.

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Wireless LANS

  • LAN

    • Within a wireless network this is easier

    • There is a physical limit to any wireless LAN technology.

      • Bluetooth – 10 Metres

      • Infrared – 1 metre

    • After these physical limits

      • The Bit Error Rate (BER) becomes too high for realistic communications to take place

        • The BER indicates what percentage of bits sent arrive at the destination in error

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Wireless LANS

  • Types of networks

    • In wired networks there is always an infrastructure

      • Even if two people bring together laptops for a game, there will be a cable and a device to repeat the signal

        • A Hub, Router or Switch on Ethernet

    • Wireless

      • This may not be the case

      • The devices may only be able to communicate for a few seconds and then they are out of range

      • People may come together for a meeting and then move away again

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Wireless LANS

  • Types of networks

    • AD-HOC

      • No pre planning of the network takes place

      • Communications may happen for hours or seconds

        • Using the Nokia N-Game with friends is an example of this

        • Business men in a meeting exchanging data

      • Difficulty in routing data to these devices

    • Infrastructured

      • The network has been planned

      • The structure would not change

        • A office would be a good example of this

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Wireless LANS

  • Ad-Hoc

    • These networks work as the devices come within the transmission distance of each other

      • When these devices can be used to extend a network

        • In this diagram device B can not reach the printer


Device B

Device A

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Wireless LANS

  • Ad-Hoc

    • One device can be used to reach the device you actually require

      • The packet is sent from device B to A and then to the printer

Device A


Device B

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Wireless LANS

  • Ad-Hoc

    • These networks are an active research area

    • The technology works now

    • The difficulty is working out a route through the network

      • The route change all of the time

      • Each time a packet is sent to sort out a route this takes battery power on all devices

      • With enough devices nothing but routing information will be sent

    • Ad-Hoc protocol

      • Mobile Ad-hoc Networks (MANET)

        • This group is standardising the IP routing protocols

          • (www.ietf.org/html.charters/manet-charter.html)

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Wireless LANS

  • Infrastructure

    • This would be used to supplement the current network

      • This allows for laptops

      • Reduces the amount of cables

        • This reduces infrastructure costs

        • Allows workers to operate where they want in the building

      • Usually combined with wired infrastructure

        • Examples would be central high power printers

    • Planning is required

      • Remember that a radio signal from one device is just interfering noise to another device

        • The more interfering devices the less successful communications that can take place

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Wireless LANS

  • Infrastructure

    • Planning is required to minimise the amount of interference

      • This can be done by increasing the distance between high users of a system

      • Different rooms for the devices

        • Some building materials will dampen the signal

        • Staffordshire University Octagon is an example of this kind building

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Wireless LANS

The Technologies

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Wireless LANS

  • Before we start on this course clarification of a widely used term the “Packet”

    • All data which is transported on a network (wired or wireless) is broken into smaller parts

    • These parts are referred to as packets

      • Each packet is then sent to the recipient

      • The packets are then reassembled into the original data

      • Packets usually consist of

        • Control information

        • The data which is being transported

        • A checksum to ensure the packet is not corrupted

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Wireless LANS

  • Infrared

    • Large installation base

      • Most devices install these ports

        • Phones

        • Laptops

        • Printers

      • Not widely used!

        • Question becomes why?

    • Standards defined By

      • Infrared Data Association (IRDA)

        • www.irda.org

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Wireless LANS

  • Infrared – Operates by line of sight

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Wireless LANS

  • Infrared

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

      • Your television remote control works in the same manner

    • Technology is suited to

      • Short distances with all devices within a room

      • It is purposely designed to operate at about 1 meter

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

    • Data Rates

      • Although IR is considered to be a slow technology it is developing

        • Serial IR – 115.2 Kbps

        • Medium ID – 1.152 Mbps

          • Rarely Used

        • Fast IR – 4 Mbps

          • Latest phones, cameras, etc support this standard

        • Very Fast IR – 16 Mbps

          • Microsoft Windows XP supported only

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Wireless LANS

  • Infrared

    • Advantage of the line of sight problem is that the communications are not shared

      • The devices need to be within a 300 arc of each other

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

    • This reduces the overhead on communications

      • Collisions do not need detecting

      • Secure communications layer does not need adding

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Data Link


Wireless LANS

  • What is a Stack?

    • The term stack refers to the Open System Interconnection (OSI) Stack

      • This is a network standard that defines what communications should take at which stage

      • There are 7 layers to the stack as shown below

      • Each layer carries out a specific task

      • Each layer can only communicate to the layer above or below

      • All other network protocols map to this stack

        • Not all layers are used with every protocol

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Data Link

Data Link



Wireless LANS

  • Communication between devices using the stack

    • Packet of information going from device 1 to device 2

Device 1


Device 2

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Wireless LANS

  • Infrared Communication Stack

    • Only the layer above and below can communicate with a point in the stack











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Wireless LANS

  • Physical

    • Defines encoding/decoding of data and transmission of the signal

    • IRLAP

      • Link Access Protocol

        • Responsible for ensuring a reliable transport of data

    • IRLMP

      • Link Management Protocol

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

    • IAS

      • Information Access Service

        • Allows knowledge of the capabilities/services of the device

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Wireless LANS

  • Optional uses of IR

    • TinyTP

      • This is a version of transport protocol designed specifically for IR

        • Flow control is offered ensuring that device buffers do not overflow

        • Maximum packet sizes are agreed by devices

        • Large packets can be broken into smaller parts

    • irOBEX

      • Object exchange protocol

        • Allows transfer of files easily between devices

    • irCOMM

      • Allows emulation of serial and parallel ports

        • The applications do not need to know that they are using IR

          • Legacy applications will work with this a printer is an example

    • irLAN

      • Allows LAN access for the devices

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

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Wireless LANS

  • So why is not widely used

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

    • Sun light

      • The sun gives off IR and as such in bright light this will effect the operation

        • Makes operation in the open awkward

    • Positioning

      • The devices need to be in line of sight, which means that they need moving from there normal position

      • The distance between the devices can effect the rate of transfer

        • Too close can be as bad as too far!

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Wireless LANS

  • Summary

    • What is a LAN

    • OSI Stack

    • Packet

    • Infrared communications