1. 1 WiFi MAC Protocol

2. 2 History WiFi is used to “describe the underlying technology of wireless local area networks (WLAN) based on the IEEE 802.11 specifications WiFi is used to “describe the underlying technology of wireless local area networks (WLAN) based on the IEEE 802.11 specifications WiFi developed by Kyle Brown WiFi developed by Kyle Brown IEEE 802.11 “denotes a set of Wireless LAN/WLAN standards developed by working group 11 of the IEEE LAN/MAN Standards Committee (IEEE 802)” IEEE 802.11 “denotes a set of Wireless LAN/WLAN standards developed by working group 11 of the IEEE LAN/MAN Standards Committee (IEEE 802)”

3. 3 First WiFi Intended for cashiers Intended for cashiers Called WaveLAN Called WaveLAN Vic Hayes Vic Hayes “Father of WiFi” Helped design IEEE 802.11b, 802.11a and 802.11g

4. 4 MAC Protocol MAC stands for Medium Access Control MAC stands for Medium Access Control Used to provide the data link layer of the Ethernet LAN system Used to provide the data link layer of the Ethernet LAN system Job is to add “a 14 byte header (Protocol Control Information (PCI)) before the data and append a 4-byte Cyclic Redundancy Check (CRC) after the data Job is to add “a 14 byte header (Protocol Control Information (PCI)) before the data and append a 4-byte Cyclic Redundancy Check (CRC) after the data

5. 5 Network-Level Architecture

6. 6 Network-Level Architecture Cont.

7. 7 IEEE 802.11 Standard PHY/MAC standard for wireless LANs PHY/MAC standard for wireless LANs First standardized in 1997 First standardized in 1997 Meet great success starting in 1999 Meet great success starting in 1999 Several working groups Several working groups IEEE 802.11a: high speed extension to the 5GHz band IEEE 802.11a: high speed extension to the 5GHz band 802.11b/g: high speed extension to the 2.4GHz band 802.11b/g: high speed extension to the 2.4GHz band 802.11e: Quality of service (QoS) enhancement (still active) 802.11e: Quality of service (QoS) enhancement (still active) 802.11i: Security enhancement 802.11i: Security enhancement 802.11s: Mesh-networking support 802.11s: Mesh-networking support Slide taken from: http://www.cse.ucsc.edu/classes/cmpe257/Spring05/lecture/lecture3.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

8. 8 Protocols Protocols Release Date Op. Frequency Date Rate (Typ) Date Rate (Max) Range (indoor) Legacy1997 2.4 – 2.5 GHz 1 Mbit/s 2 Mbit/s ? 802.11a1999 5.15-5.35/5.47- 5.725/5.725- 5.875 GHz 25 Mbit/s 54 Mbit/s ~30 meters (~100 feet) 802.11b1999 2.4 – 2.5 GHz 6.5 Mbit/s 11 Mbit/s ~50 meters (~150 feet) 802.11g2003 2.4 – 2.5 GHz 11 Mbit/s 54 Mbit/s ~30 meters (~100 feet) 802.11n 2006 (draft) 2.4 GHz or 5GHz bands 200 Mbit/s 540 Mbit/s ~50 meters (~160 feet)

9. 9 Protocols

10. 10 IEEE 802.11 Group Standards IEEE 802.11The original 1 Mbit/s and 2 Mbit/s, 2.4 GHz RF and IR standard (1999) IEEE 802.11a54 Mbit/s, 5 GHz standard (1999, shipping products in 2001) IEEE 802.11bEnhancements to 802.11 to support 5.5 and 11 Mbit/s (1999) IEEE 802.11cBridge operation procedures; included in the IEEE 802.1D standard (2001) IEEE 802.11dInternational (country-to-country) roaming extensions (2001) IEEE 802.11eEnhancements: QoS, including packet bursting (2005) IEEE 802.11fInter-Access Point Protocol (2003) Withdrawn February 2006 IEEE 802.11g54 Mbit/s, 2.4 GHz standard (backwards compatible with b) (2003) IEEE 802.11hSpectrum Managed 802.11a (5 GHz) for European compatibility (2004) IEEE 802.11iEnhanced security (2004) IEEE 802.11jExtensions for Japan (2004)

11. 11 IEEE 802.11 Group Standards Cont. IEEE 802.11kRadio resource measurement enhancements IEEE 802.11l(reserved and will not be used) IEEE 802.11mMaintenance of the standard; odds and ends. IEEE 802.11nHigher throughput improvements using MIMO (multiple input, multiple output antennas) IEEE 802.11o(reserved and will not be used) IEEE 802.11p WAVE - Wireless Access for the Vehicular Environment (such as ambulances and passenger cars) IEEE 802.11q(reserved and will not be used, can be confused with 802.1Q VLAN trunking) IEEE 802.11rFast roaming Working "Task Group r" IEEE 802.11sESS Mesh Networking IEEE 802.11TWireless Performance Prediction (WPP) - test methods and metrics Recommendation IEEE 802.11uInterworking with non-802 networks (for example, cellular) IEEE 802.11vWireless network management IEEE 802.11wProtected Management Frames IEEE 802.11x(reserved and will not be used) IEEE 802.11y3650-3700 Operation in the U.S.

12. 12 802.11 Protocol Entities Slide taken from: http://www.cse.ucsc.edu/classes/cmpe257/Spring05/lecture/lecture3.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

13. 13 MAC in Detail Channel access mechanism Channel access mechanism Distributed Coordination Function (DCF) Distributed Coordination Function (DCF) Carrier sense multiple access (CSMA) with immediate MAC-level ACK Carrier sense multiple access (CSMA) with immediate MAC-level ACK RTS/CTS(4-way handshaking) exchange (optional) RTS/CTS(4-way handshaking) exchange (optional) RTS stands for Request-to-Send RTS stands for Request-to-Send CTS stands for Clear-to-Send CTS stands for Clear-to-Send Point Coordination Function (PCF) Point Coordination Function (PCF) Polled access through AP and distributed access Polled access through AP and distributed access Contention-free period (CFP) and contention period (CP) Contention-free period (CFP) and contention period (CP) Seldom implemented in practice Seldom implemented in practice Slide taken from: http://www.cse.ucsc.edu/classes/cmpe257/Spring05/lecture/lecture3.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

14. 14 CSMA/CA Explained Reduce collision probability where mostly needed Reduce collision probability where mostly needed Stations are waiting for medium to become free Stations are waiting for medium to become free Select Random Backoff after a Defer, resolving contention to avoid collisions Select Random Backoff after a Defer, resolving contention to avoid collisions Efficient Backoff algorithm stable at high loads Efficient Backoff algorithm stable at high loads Exponential Backoff window increases for retransmissions Exponential Backoff window increases for retransmissions Backoff timer elapses only when medium is idle Backoff timer elapses only when medium is idle Implement different fixed priority levels Implement different fixed priority levels To allow immediate responses and PCF coexistence To allow immediate responses and PCF coexistence Slide taken from: http://www.cse.ucsc.edu/classes/cmpe257/Spring05/lecture/lecture3.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

15. 15 CSMA/CA + ACK Protocol Defer access based on Carrier Sense Defer access based on Carrier Sense Clear Channel Assessment (CCA) from PHY and Virtual Carrier Sense state Clear Channel Assessment (CCA) from PHY and Virtual Carrier Sense state Direct access when medium is sensed free longer then DIFS, otherwise defer and backoff Direct access when medium is sensed free longer then DIFS, otherwise defer and backoff Reciever of directed frames to return an ACK immediately when CRC correct Reciever of directed frames to return an ACK immediately when CRC correct When no ACK received then retransmit frame after a random backoff (up to maximum limit) When no ACK received then retransmit frame after a random backoff (up to maximum limit) Slide taken from: http://www.cse.ucsc.edu/classes/cmpe257/Spring05/lecture/lecture3.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

16. 16 CSMA/CD CSMA stands for Carrier Sense Multiple Access CSMA stands for Carrier Sense Multiple Access CD stands for Collision Detection CD stands for Collision Detection Allows for Retransmission Back-Off Allows for Retransmission Back-Off

17. 17 RTS/CTS Based Access Duration field in RTS and CTS frames distribute Medium Reservation information which is stored in a Net Allocation Vector (NAV) Duration field in RTS and CTS frames distribute Medium Reservation information which is stored in a Net Allocation Vector (NAV) Defer on either NAV or “CCA” indicating Medium Busy Defer on either NAV or “CCA” indicating Medium Busy Use RTS/CTS is optional but must be implemented Use RTS/CTS is optional but must be implemented Use is controlled by a RTS_Threshold parameter per station Use is controlled by a RTS_Threshold parameter per station To limit overhead for short frames To limit overhead for short frames Slide taken from: http://www.cse.ucsc.edu/classes/cmpe257/Spring05/lecture/lecture3.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

18. 18 Frame Formats MAC Header format differs per Type: MAC Header format differs per Type: Control Frames (several fields are omitted) Control Frames (several fields are omitted) Management Frames Management Frames Data Frames Data Frames Includes Sequence Control Field for filtering of duplicates caused by ACK mechanism Includes Sequence Control Field for filtering of duplicates caused by ACK mechanism Slide taken from: http://www.cse.ucsc.edu/classes/cmpe257/Spring05/lecture/lecture3.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

19. 19 Address Field Description Addr 1 = All stations filter on this address. Addr 1 = All stations filter on this address. Addr 2 = Transmitter Address (TA) Addr 2 = Transmitter Address (TA) Identifies transmitter to address the ACK frame to Identifies transmitter to address the ACK frame to Addr 3 = Dependent on To and From DS bits Addr 3 = Dependent on To and From DS bits Addr 4 = Only needed to identify the original source of WDS (Wireless Distribution System) frames Addr 4 = Only needed to identify the original source of WDS (Wireless Distribution System) frames Slide taken from: http://www.cse.ucsc.edu/classes/cmpe257/Spring05/lecture/lecture3.pdf#search='802.11e%20MAC%20protocol%2C%20powerpoint

20. 20 Applications Wireless Access Point (WAP) Wireless Access Point (WAP) Wireless Routers Wireless Routers Wireless Ethernet Bridge Wireless Ethernet Bridge Range Extender Range Extender

21. 21 Gaming Applications Nintendo DS Nintendo DS Sony PSP Sony PSP Xbox 360 Xbox 360 Playstation 3 Playstation 3 Nintendo Wii Nintendo Wii

22. 22 Problems / Performance Issues Interruption by other devices Interruption by other devices High power consumption High power consumption When setup the network defaults to open mode When setup the network defaults to open mode Large area coverage Large area coverage

23. 23 Security Issues WEP encryption is breakable WEP encryption is breakable Spoofing authorized MAC addresses Spoofing authorized MAC addresses Wardriving and Warchalking Wardriving and Warchalking

24. 24 Question Summary / Conclusion What is WiFi MAC Protocol? What is WiFi MAC Protocol? It is the underlying technology of wireless local area networks (WLAN) based on the IEEE 802.11 specifications that provides the data link layer of the Ethernet LAN system. It is the underlying technology of wireless local area networks (WLAN) based on the IEEE 802.11 specifications that provides the data link layer of the Ethernet LAN system. Who came up with WiFi MAC Protocol? Who came up with WiFi MAC Protocol? The IEEE Task Groups and created the IEEE 802.11 or IEEE 802.11x Committee, however IEEE only sets specifications. WiFi Alliance runs the certification program. The IEEE Task Groups and created the IEEE 802.11 or IEEE 802.11x Committee, however IEEE only sets specifications. WiFi Alliance runs the certification program. What is the difference between DCF and PCF? What is the difference between DCF and PCF? DCF uses carrier sense multiple access with immediate MAC-level ACK and contains RTS/CTS optional exchange. PCF uses polled access through AP and distributed access; cotains a contention-free period and a contention period; and is seldom implemented in practice. DCF uses carrier sense multiple access with immediate MAC-level ACK and contains RTS/CTS optional exchange. PCF uses polled access through AP and distributed access; cotains a contention-free period and a contention period; and is seldom implemented in practice.

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