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IEEE 802.11 Standards

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  1. IEEE 802.11 Standards Fundamentals of Mobile Computing Justin Champion, C203, Beacon Building

  2. FMC - Contents • What is the IEEE • Why the standard was created • What standards are there for 802.11 • Use of 802.11 • Security within these standards • Future of 802.11

  3. FMC – What is the IEEE • Institute of Electrical and Electronic Engineers (IEEE) • These are a not for profit standards group • Based in America • Worldwide Membership • Standards they develop effect the rest of the world • List of current IEEE standards http://info.computer.org/standards/standesc.htm • One of the standards is IEEE 802.3 (Ethernet) networks • The most widely used type of LAN wired networking at the moment

  4. FMC – Ethernet • Ethernet has become the dominant wired standard for network communications used for • Homes • Offices • Universities • Large organisations • Advantages is that it is now relatively cheap to install and maintain • Due to the large user base • High speed achievable for the cost • 10 Mbps, 100 Mbps, Gigabit +

  5. FMC – Releasing the user • Realisation • of allowing user to increase there portability • Device technology became available to allow the user to move • Laptops with • Increased processing • Increased memory • Increased Storage • Operating Systems to support the functionality away from the desktop machines • Ethernet networks would need to support this

  6. FMC – Releasing the user • Original Specification for 802.11 • Was ratified in 1997 • Original specifications was for Infrared and Radio based • We will concentrate on the radio based • Data rate was 1 Mbps or 2 Mbps • 1 Mbps uses Binary Phase Shift Keying (BPSK) • 1 bit per change in the carrier sine wave • 2 Mbps uses Quadrature Phase Shift Keying (QPSK) • 2 bits per change in the carrier sine wave • Operates at 2.4 GHz (ISM Band) • Discussed on next slide • Was not fast enough for general office use as fixed networks developed • New standards were required with higher speed • 802.11b • 802.11a • 802.11g

  7. Wireless LANS - ISM • Industrial Scientific and Medical (ISM) • Intended as worldwide free usage radio band • No license required • Defined worldwide by the ITU for non commercial use • There are some changes worldwide in this frequency • Commonly refers to the frequency 2.4 GHz • There are other frequencies • 900 MHz • 5.8 GHz • Widely used for • Wireless LAN technology • Same frequency as • Microwave Ovens • Cordless Phones • Other wireless Devices • These do give for interference problems, particularly at the moment with the 2.4 GHz range

  8. FMC – Effects • 802.11 standards effect the OSI stack at • Data Link Layer (layer 2) • Assemble/disassemble frames • Addressing and error detection • Manage access to media • Interface with higher layers • Physical Layer (layer 1) • Encoding/decoding signals • Preamble (for synchronization) • Bit transmission/reception Application Presentation Session Transport Network Data Link Physical

  9. FMC – Releasing the user • 802.11 Frame types • Management • These are frames which are used to send transport information between nodes • Control • These are used to control access to the Medium • Data • Transporting of the information between nodes

  10. Wireless LANS • 802.11 Data Frame • Only the data part is sent at full speed in 802.11b • The header and synchronisation bits is sent at 1 Mbps • In newer versions (G, A) all of it is sent at full speed • Address 1 • Source Address • Address 2 • Destination Address • Address 3 • Receiving wireless station • Address 4 • Transmitting wireless station

  11. FMC – 802.11 Standards • The 802.11 group has produced a number of standards • For LAN network communication • Power Saving Techniques • Quality of Service • Wireless Security

  12. FMC – 802.11 Standards • 802.11 • The original 2 Mbit/s, 2.4 GHz standard • 802.11a • 54 Mbit/s, 5 GHz standard • 802.11b • Enhancements to 802.11 to support 5.5 and 11 Mbit/s • 802.11e • Enhancements: QOS, including packet bursting • 802.11f • Inter-Access Point Protocol (IAPP) • 802.11g • 54 Mbit/s, 2.4 GHz standard (backwards compatible with b) • 802.11h • 5 GHz spectrum, Dynamic Channel/Frequency Selection (DCS/DFS) and Transmit Power Control (TPC) for European compatibility • 802.11i • Enhanced security • 802.11n • Higher throughput improvements, stream multiplexing • 802.11s • Mesh Networks

  13. FMC - Wireless LANS • 802.11 common LAN standards • A • 1999 • Operates in the 5.8GHz frequency • Maximum throughput is 54 Mbps • Encoding method is Orthogonal Frequency Division Multiplexing (OFDM) • B • 1999 • Most widely used and standardised • Operates in the ISM band 2.4 Ghz • Maximum throughput of 11 Mbps • Encoding method is Direct Sequence Spread Spectrum (DSSS) • G • Latest operational standard (June 2003) • Operates in the 2.4 GHz frequency • Maximum throughput is 54 Mbps • Encoding method is Orthogonal Frequency Division Multiplexing (OFDM) • Backwards compatible with 802.11b

  14. FMC - Wireless LANS • Wi-Fi 802.11b transmissions • Carried out using Direct Sequence Spread Spectrum (DSSS) • The original signal is XOR’d with a code word • The code word is referred to as the Barker Code • Barker code is a 11 bit sequence (10110111000) • This allows improved reliability in data transmission rather than just sending data. • A wider bandwidth is required for the transmission • Data can be restored even if small errors occur in the transmission • The receiver puts this information back together again, with the code • This method is used due to the ability to send large amounts of data at once

  15. FMC - Wireless LANS • Wi-Fi 802.11A, G transmissions • Orthogonal Frequency Division Multiplexing (OFDM) • Allows a large number of carriers split by an exact frequency • Each of these carriers can be demodulated independently • Best way of visualizing this is as a large number of small modems • They are all working at the same time transferring small amounts of information • When the transferred information is brought together a large amount of information is transferred • This technique is also used in ADSL modems • Very good interactive demonstration by Edinburgh university • http://www.see.ed.ac.uk/~acmc/OFDMTut.html

  16. FMC - Wireless LANS Bandwidth In the event of consistent errors the communication medium will move to a slower but more reliable method of transfer 802.11b for example 11 Mbps 5.5 Mbps 1 Mbps

  17. Wireless LANS • 802.11 • Operates • In the same manner as the Ethernet networks • A single shared medium for transmission, in our case Air, for wired Ethernet a copper cable • Only one device can use the same frequency/channel at any time therefore • A device waits for silence on the radio interface before communicating • Carrier Sense Multiple Access (CSMA) Collision Avoidance (CA) • A wireless node can not detect if other nodes are transmitting outside of its range • This the “Hidden Terminal” problem which was discussed by Kelvin • Also corruption can not be detected by the transmitting node

  18. Wireless LANS • Hidden Terminal

  19. Wireless LANS • Preventing air interface collisions • Permission is requested to transmit CSMA Access Point RTS CTS RTS = Request to Send Data CTS = Clear to Send ACK = Acknowledgment ACK

  20. Wireless LANS - Channels • As discussed before just because ISM is an international standard does NOT mean it is the same everywhere • If we take IEEE 802.11b standard • Europe • 13 Channels • Maximum 100 milliwatt (0.1 Watt) • Japan • 14 Channels • Maximum 10 milliwatt (0.01 Watt) • USA • 11 Channels • Maximum 1000 milliwatt (1 Watt) • Spain • 2 Channels • The only channels which are available globally are 10 and 11 • This is a consideration if you are moving access point kit between countries

  21. Wireless LANS • Operates in • AD-Hoc mode • No infrastructure is in place • The users come together communicate and then part, mutli-hop networking is possible and adhoc routing • Uses a Access point (AP) to allow connection to wired infrastructure • This is the way that 802.11 is used in this university. • An “access point” is provided • This is a point which the wireless network can connect to the wired infrastructure • The access point is also a point of control for the network • Controlling which device communicates at any time

  22. Wireless LANS

  23. Wireless LANS • Is Wi-Fi the same as IEEE 802.11 ? • Wireless Fidelity (Wi-Fi) • Is a group which approves implementation of standards started in 1999 • http://wi-fi.org/ • IEEE specifies the standards, but does not check that manufacturers implement them • Any product which has this logo, is assured to interoperate with other products in the same category • Only devices which have been approved can show the logo • In reality there will always some differences in performance between manufacturers

  24. Wireless LANS - Security • 802.11 • Wired Equivalent Privacy (WEP) • Uses either 40 or 128 bit RS4 symmetric encryption • The standard does not define how to distribute the keys! • Discussion of cracking the encryption algorithm real-time! • http://www.isaac.cs.berkeley.edu/isaac/wep-faq.html, 2003) • When used 40 Bit encryption reduces throughput by 20 - 50% • Trying to avoid the Pringle situation, which was embarrassing for the technology and users of it • news.bbc.co.uk/1/hi/sci/tech/1860241.stm, 2002) • War Driving, users accessing wireless networks without permission • Wi-Fi is targeted with wall chalking indicating locations to connect • The technology is targeted as it is widely used and available • Radio Signal Propagation • Radio signals can not be restricted to a geographic area without expensive specially built buildings

  25. Wireless LANS - Security • 802.11i • Wi-Fi Protected Access (WPA) and WPA2 • WPA2 was agreed June 2004 matching the requirements 802.11i producing an improved security standard • WPA • Requires only a software or firmware upgrade • Is intended to operate with a 802.1 authentication server • It was recognised early though that this would not always be possible • Encryption can be done via a shared secret between devices • Temporal keying • Allows the keys to be changed as the communications take place • Improved Encryption algorithm used • WPA 2 • Is much securer by using improved encryption algorithms • These do need a decryption/encryption co-processor • Will support roaming of devices

  26. Wireless LANS • Wi-Fi – unsecured access points are available to everyone • Radio signals are not limited to buildings unlike wired networks • War chalking indicates open access points • http://en.wikipedia.org/wiki/War-chalking

  27. Wireless LANS • 802 wireless future • IEEE 802.16 (WiMax) • 802.16a is intended as a wireless metropolitan technology • First devices appeared in Late 2006 • news.zdnet.co.uk/communications/wireless/0,39020348,39184894,00.htm • In August 2008 on communication is offering this service in Leeds max 10 mbps • http://www.on-communications.com/news-detail.php?news_id=13 • Intel are discussed on the 31st Oct 2007 looking into rolling out WiMax in Africa • http://news.bbc.co.uk/1/hi/technology/7070859.stm • Allows 120 Mbps • Uses the 10 to 66 GHz frequency • This will require no interference, so transmitters and receivers will need to be placed on the roof • Transmission up to 30 Miles • Currently a limit on receivers which is in the hundreds • Standards Group • grouper.ieee.org/groups/802/16/index.html

  28. Wireless LANS – Latest Standard • As with wired networks the throughput of the networks is always increasing • The current highest throughput is 802.11a and G at 54 Mbps • 802.11N which is still under discussion will give a throughput of a predicted 384 Mbps in the same LAN environment • The final draft of the standard was due to be released November 2005 • The actual draft was actually released the 27th of Jan 2006 • Which is very good for the IEEE standards group • http://www.theregister.co.uk/2006/01/20/802-11n_wifi_spec_agreed/ • The final ratification of the standard is expected March 2009 • http://grouper.ieee.org/groups/802/11/Reports/802.11_Timelines.htm • At the moment it is possible to purchase what are referred to as 802.11 pre N products • These are based on the current draft proposal and on this basis could be incompatible when the actual devices are agreed upon • Here is a review of a recent 802.11 pre N product • http://www.pcworld.com/article/145098/new_80211n_routers_the_best_wifi_yet.html# http://www.linux-user.de/ausgabe/2004/12/022-wlan/Belkin-PreN.jpg

  29. Wireless LANS • Expansion of the network 802.11 networks • BTFON (November 07) • British Telecom (BT) and Foneros (FON) • Have configured the wireless network hubs of users who agree to share there network connection to allow any user to make use of the access point • The concept is increase the number of usable access points across the country • Allowing increased use of this technology • Users can subscribe to make use of these access points or if you donate by allowing your access point to be a part of the network you get access for free. • The communications are through a separate channel and as such are blocked from communicating with any device on your network • Also for legal reasons you would also not be responsible for the content the user requests • The throughput is limited to 512kbps which is more than enough for most users • http://www.btfon.com/ • Additional services come from thecloud in London as a good example of using this tech • http://www.thecloud.net/page/1796/

  30. Wireless LANS – Market Place • Wi-Fi dominates the Local Area Networks currently • This would be expected to continue • Other technologies like Hyperlan 1 & 2 are now not really likely to control the market • Original issues with 802.11 standards are now being resolved • Security • Battery usage • Roaming capabilities • Quality of Service (QOS) • Good source of information • http://www.wi-fiplanet.com/ • New Games consoles are using this technology • Sony PS3 uses the 802.11B/G standards

  31. Wireless LANS - Future • The future of 802.11 is looking good • Increasing number of devices are making use of this technology • With some of the developments like better battery usage more device still will operate • Consider your digital camera with 802.11b inside you could purchase a coffee and FTP your pictures to your home computer • http://www.unbeatable.co.uk/news/Canon-unveil-the-latest-Canon-WiFi-Digital-Camera/281215.html • It is a major competing technology with 3G, with the limits being looked at by various groups the future will be interesting • An increasing number of mobile phones now support 802.11b at least • This will impact on the profitability of the cellular operators as 802.11b has a considerably higher throughput

  32. FMC – Conclusion • Conclusion • What is the IEEE • Why the standard was created • What standards are there for 802.11 • Use of 802.11 • Future of 802.11