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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

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

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

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

Printer

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
wireless lans18

Application

Presentation

Session

Transport

Network

Data Link

Physical

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
wireless lans19

Application

Application

Presentation

Presentation

Session

Session

Transport

Transport

Network

Network

Data Link

Data Link

Physical

Physical

Wireless LANS
  • Communication between devices using the stack
    • Packet of information going from device 1 to device 2

Device 1

Logically

Device 2

wireless lans20
Wireless LANS
  • Infrared Communication Stack
    • Only the layer above and below can communicate with a point in the stack

IAS

irLAN

OBEX

irCOMM

TinyTP

Optional

irLMP

Required

irLAP

Physical

wireless lans21
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
wireless lans23
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
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