IEEE 802.11 Standards

Fundamentals of Mobile Computing

Justin Champion, C203, Beacon Building

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

Hidden Terminal

Device 2Access Point

Device 1

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

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