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Wireless LANS

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

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  1. Wireless LANS Justin Champion Room C208 - Tel: 3273 www.staffs.ac.uk/personal/engineering_and_technology/jjc1

  2. Wireless LANS • Contents • What is a LAN • Types of wireless LAN • AdHoc • Infrastructured • Infrared Communications • Uses of these technologies

  3. 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

  4. 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.

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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)

  11. 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

  12. 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

  13. Wireless LANS The Technologies

  14. 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

  15. 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

  16. Wireless LANS • Infrared – Operates by line of sight

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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!

  25. Wireless LANS • Summary • What is a LAN • OSI Stack • Packet • Infrared communications

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