1. Copyright © 2002 Intel Corporation. The 802.11 MAC Protocol & Quality of Service Duncan Kitchin Wireless Networking Group Intel Corporation 4/4/2003

2. Wireless Networking Division Intel Confidential Page 2 Agenda 802.11 MAC Overview QoS Objectives & Applications Important Questions 802.11e Details Future Developments & Summary

3. Copyright © 2002 Intel Corporation. 802.11 MAC Overview

4. Wireless Networking Division Intel Confidential Page 4 802.11 Logical Architecture Physical Data link Network Transport Session Presentation Application PHY MAC LLC (802.2)

5. Wireless Networking Division Intel Confidential Page 5 802.11 sublayers PHY MAC Higher layers Extensions are “mix and match” 802.11a 802.11b 802.11g 802.11d 802.11e 802.11h 802.11i 802.11c 802.11F

6. Wireless Networking Division Intel Confidential Page 6 Standards decoder ring 802.11a5GHz OFDM PHY 802.11b2.4GHz CCK PHY 802.11c802.11 bridging 802.11dInternational roaming 802.11eQoS/efficiency enhancements 802.11FInter AP protocol 802.11g2.4GHz OFDM PHY 802.11h5GHz regulatory extensions 802.11iSecurity enhancements 802.11jJapan 5GHz band extensions 802.11kRadio resource measurement 802.11lSkipped (typographically unsound) 802.11mMaintenance 802.11nHigh throughput PHY

7. Wireless Networking Division Intel Confidential Page 7 Origins of the 802.11 MAC Derived from Ethernet (CSMA/CD) philosophy Developed into present form 1990-1994 Required much modification to fit wireless medium –CSMA/CA Widely regarded at the time as a kludge

8. Wireless Networking Division Intel Confidential Page 8 New 802.11 MAC developments 802.11e is the “new” MAC –evolution to base 802.11 –adds differentiated QoS… –…but also enhanced efficiency Core components represent a simple evolution Optional extensions may be widely implemented in the future, subject to market demand

9. Copyright © 2002 Intel Corporation. QoS Objectives & Applications

10. Wireless Networking Division Intel Confidential Page 10 What Does QoS Mean? We limit the definition to mean “delivering traffic for real-time applications” Each application has a requirements tuple –max latency –min data rate –max packet drop probability The set of tuples define points that delimit the requirements curve

11. Wireless Networking Division Intel Confidential Page 11 Representation of Requirements Define a set of applications first –voice –gaming –real-time video (videoconferencing) –“CD like” audio –“Television/VCR like” video Each of these applications defines a point on the data rate/latency/drop rate requirements curve

12. Wireless Networking Division Intel Confidential Page 12 Why 802.11e and 802.11a Home wireless network usage model shift 802.11b in home networks was driven by broadband Internet connection sharing 802.11a in home networks will be driven by high bandwidth multimedia streams between devices in the home

13. Wireless Networking Division Intel Confidential Page 13 New Usage Models BB Gateway PC TV Tablet

14. Wireless Networking Division Intel Confidential Page 14 Applications Video Audio Voice Gaming Videoconferencing

15. Wireless Networking Division Intel Confidential Page 15 Video Key motivation for multimedia home networks High quality, streaming video Focus on MPEG-2, MPEG-4, wmv Lowest mean rate 2Mb/s (SD) Highest mean rate 20Mb/s (HD) Variable data rate requirements

16. Wireless Networking Division Intel Confidential Page 16 Audio High quality, streaming audio has distinct requirements from voice Key formats MP3, wma, PCM Bandwidth range 64kb/s up to 1.5Mb/s Relatively high latency tolerance

17. Wireless Networking Division Intel Confidential Page 17 Voice & videoconferencing Low latency –< 50ms required Lower bandwidth requirements –32kb/s and lower for voice –128kb/s for videoconferencing Higher tolerance to frame losses

18. Wireless Networking Division Intel Confidential Page 18 Gaming Lowest latency –< 10ms required Lower bandwidth requirements –32kb/s – 128kb/s? Low tolerance to frame loss

19. Wireless Networking Division Intel Confidential Page 19 Applications Summary Latency tolerance Bandwidth Voice Videoconference VideoAudio Gaming

20. Copyright © 2002 Intel Corporation. Important Questions

21. Wireless Networking Division Intel Confidential Page 21 The Protocol Stack PHY DLC (MAC + LLC) Network Transport Application IP TCP/UDP

22. Wireless Networking Division Intel Confidential Page 22 The Protocol Stack Before defining the link layer (MAC) must decide what the higher layers are If we assume TCP/IP based higher layers, that imposes restrictions on what we can do We don’t have latitude to rewrite TCP/IP, or the interface to it We also don’t have latitude to rewrite the applications or the OS

23. Wireless Networking Division Intel Confidential Page 23 What We Must Do Define 802.11 MAC as providing a set of services Those services are defined by the 802.2 service primitives, incorporating 802.1D Deliver packets, each of which is tagged with a 3-bit priority Consider each service request packet-by- packet –we have no mechanism to tell us about connections from the higher layers

24. Wireless Networking Division Intel Confidential Page 24 What the Services Will Look Like in QoS Terms Each packet, dependent on priority, will have a latency probability distribution If the higher layers (or the MAC) imposes a timeout, there will be a drop probability against timeout curve Need to revisit requirements to see what the bounds for the curve should be

25. Copyright © 2002 Intel Corporation. 802.11e Details

26. Wireless Networking Division Intel Confidential Page 26 802.11e features EDCF/WME Core functionality Point coordinated mode Group acknowledge Direct link

27. Wireless Networking Division Intel Confidential Page 27 802.11e Features CSMA Direct link Block acknowledge Point coordinated mode

28. Wireless Networking Division Intel Confidential Page 28 CSMA Strategy Use 802.1D tags to classify traffic into groups with widely differing requirements 8 priority levels grouped into four classes –best effort –video/audio probe –video/audio –voice/gaming

29. Wireless Networking Division Intel Confidential Page 29 Applying to different classes Priority access improves chances of getting access to the medium quickly Long burst duration provides high bandwidth access, but at the expense of latency Set appropriately: –voice/gaming has very high access priority, small burst size –video/audio has much lower access latency (but better than best effort) but large burst sizes

30. Wireless Networking Division Intel Confidential Page 30 802.11e Direct Link 802.11-1997 specification permits traffic in an AP-based network between clients and AP only 802.11e adds capability for clients to send traffic directly to each other –improves bandwidth efficiency, particularly in home networks

31. Wireless Networking Division Intel Confidential Page 31 Direct Link AP Station