The IEEE 802 11 Specification By Matthew Ruston

The IEEE 802. 11 Specification By Matthew Ruston November 25, 2007

Overview � Introduction to 802. 11 Wireless Networking � Specification History � High-level Architecture � Physical Architecture � Data Link Architecture

802. 11 Wireless Networking � Revolutionized wireless communication � Allows compliant devices to communicate using radio transmissions are specific frequencies. � Found in: �Automobiles �Digital Cameras �Printers �Cell Phones

Specification History � First IEEE 802. 11 standard released in 1997 �Maximum data rate: 2 Mbps � 2. 4 Ghz band �Indoor Range: 20 meters �Outdoor Range: 100 meters

Specification History � IEEE 802. 11 a released in 1999 �Maximum data rate: 54 Mbps � 5. 1 - 5. 8 Ghz band �Indoor range: 35 meters �Outdoor range: 120 meters �Limited indoor effectiveness due to high frequency use

Specification History � IEEE 802. 11 b also published in 1999 �Maximum data rate: 11 Mbps � 2. 4 Ghz band �Indoor Range: 38 meters �Outdoor Range: 140 meters

Specification History � IEEE 802. 11 g released in 2003 �The current industry adopted specification �Maximum data rate: 54 Mbps � 2. 4 Ghz band (backwards compatible with 802. 11 b) �Indoor range: 38 meters �Outdoor range: 140 meters

802. 11 Architecture �A 802. 11 compliant network design can be partitioned into a set of various objects.

802. 11 Architecture � The 802. 11 specification fits perfectly within the OSI networking model. Thus common place protocols such as TCP or UDP are not effected by the use of a 802. 11 network. Application Presentation Session Transport Network Data Link Physical 802. 3 Ethernet 802. 11 Wireless

802. 11 Physical Layer Architecture � Relies on encoding radio waves with binary information to send datagrams. � Multiple methods implemented by the various 802. 11 specifications.

802. 11 Physical Architecture � Uses the Frequency Hopping Spread. Spectrum (FHSS) specification to transmit encoded information. �A device will ‘hop’ between a predetermined and configured set of frequency channels during the transmission. �If one of the channels has interference or noise this communication protocol will ensure that the majority of the information can still transmit successfully.

802. 11 Physical Architecture � To encode information into the transmission a system called Gaussian Frequency Shift Keying (GFSK) is used. �Best explained if illustrated…

802. 11 b Physical Architecture � Uses a method called Differential Phase Shift Keying (DPSK) to encode information into it’s 2. 4 Ghz band. �Uses phase shifts of the carrier wave to encode a binary message. Design again, best illustrated… Symbol Phase Shift 00 0 01 Π/2 radians 11 Π radians 10 3 Π/2 or – Π/2 radians

802. 11 a/g Physical Architecture � Although they are not backwards compatible they use Orthogonal Frequency Division Multiplexing for a transmission protocol. �Has been omitted due to complexity.

802. 11 Data Link Architecture � Much like 802. 2, the Ethernet specification, 802. 11 relies on Frames to encompass a single datagram. � Ethernet Frame: Preamble Dest. Address Source Address Type Data 8 bytes 6 bytes 2 46 -1500 bytes CRC 4 bytes

802. 11 Data Link Architecture � 802. 11 Frame Control Duration Address 1 Address 2 Address 3 Seq. Control Address 4 Payload CRC 2 bytes 6 bytes 2 bytes 6 byes 0 -2312 bytes � 802. 11 6 bytes Frame Control Breakdown Protoco Type l Version Subtyp e To DS From DS More Frag. Retry Power Mgt. More Data WEP Order 2 bits 4 bits 1 bit 1 bit 2 bits

802. 11 Data Link Architecture � To help illustrate the data link architecture, Wireshark was used to capture and analyze information from a 802. 11 datagram.

802. 11 Data Link Transport � 802. 11 uses CSMA/CA for datagram transmission management. �Carrier Sense Multiple Access With Collision Avoidance �Each wireless device with ‘sense’ the radio channel before transmission. If it appears busy it will wait a short random amount of time before retesting the channel.

802. 11 Data Link Transport � ‘Collision Avoidance’ is implemented by using two special frames between a wireless device and its associated access point (AP). �Device wishing to transmit will send a Request To Send frame to the AP. �If the AP deems the channel available it will respond with a Clear To Send frame to the device.

[1] IEEE Computer Society, IEEE-SA Standards Board, “Information technology – Telecommunications and information exchange between systems – Local and metropolitan area networks – Specific requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”. 1999, Reaffirmed June 2003. IEEE-SA Standards Board. [http: //standards. ieee. org/getieee 802/download/802. 11 -1999. pdf]. Accessed Nov. 18, 2007. [2] IEEE Computer Society, IEEE-SA Standards Board, “Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications—Amendment 1: Highspeed Physical Layer in the 5 GHz band”. 1999, Reaffirmed June 2003. [http: //standards. ieee. org/getieee 802/download/802. 11 a-1999. pdf]. Accessed Nov. 18, 2007. [3] IEEE Computer Society, IEEE-SA Standards Board, “Supplement to IEEE Standard for Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Higher-Speed Physical Layer Extension in the 2. 4 GHz Band”. 1999, Reaffirmed June 2003. [http: //standards. ieee. org/getieee 802/download/802. 11 b-1999. pdf]. Accessed Nov. 18, 2007. [4] IEEE Computer Society, IEEE-SA Standards Board, “IEEE Standard for Information technology— Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications—Amendment 4: Further Higher-Speed Physical Layer Extension in the 2. 4 GHz Band”. 2003. [http: //standards. ieee. org/getieee 802/download/802. 11 g-2003. pdf]. Accessed Nov. 18, 2007.