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

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

Copyright © 2002 Intel Corporation MAC Overview

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

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

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

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

Wireless Networking Division Intel Confidential Page 8 New MAC developments e is the “new” MAC –evolution to base –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

Copyright © 2002 Intel Corporation. QoS Objectives & Applications

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

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

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

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

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

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

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

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

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

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

Copyright © 2002 Intel Corporation. Important Questions

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

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

Wireless Networking Division Intel Confidential Page 23 What We Must Do Define MAC as providing a set of services Those services are defined by the 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

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

Copyright © 2002 Intel Corporation e Details

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

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

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

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

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

Wireless Networking Division Intel Confidential Page 31 Direct Link AP Station