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 Device B Device A Printer

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 B Device A Printer

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 30 0 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. 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 Physical Data Link Network Transport Session Presentation Application

20. Wireless LANS  Communication between devices using the stack  Packet of information going from device 1 to device 2 Physical Data Link Network Transport Session Presentation Application Physical Data Link Network Transport Session Presentation Application Device 1 Device 2 Logically

21. Wireless LANS  Infrared Communication Stack  Only the layer above and below can communicate with a point in the stack IAS irLMP irLAP Physical TinyTP irLANOBEXirCOMM Required Optional

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