ieee 802.11 standards
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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
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
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 +
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
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
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
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
Physical
Data Link
Network
Transport
Session
Presentation
Application
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
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
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
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
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
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
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
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
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
Wireless LANS Preventing air interface collisions
Permission is requested to transmit
CSMARTS
CTS
Data
ACK
Access Point
RTS = Request to Send
CTS = Clear to Send
ACK = Acknowledgment
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
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
Wireless LANS
Ethernet
802.11b Access Point
PrinterUniversity Web Server
COMPAQ
Gateway to Internet
Internet
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
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
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
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
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
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
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/
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
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
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