MAC improvement using random AIFSN May 2006 doc.: IEEE 802.11-06/0657r0 May 2006 MAC improvement using random AIFSN Date: 2006-05-13 Authors: Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair <stuart.kerry@philips.com> as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <patcom@ieee.org>. Todor Cooklev Todor Cooklev

May 2006 doc.: IEEE 802.11-06/0657r0 May 2006 Abstract We discuss contention among streams of equal priority in the digital home. Next, we propose the use of random AIFSN as a solution, with draft text. Simulation results indicating the performance improvement are also included. The proposed scheme performs especially well under heavy channel loads. Todor Cooklev Todor Cooklev

Outline Contention in 802.11 scenarios for digital home May 2006 doc.: IEEE 802.11-06/0657r0 May 2006 Outline Contention in 802.11 scenarios for digital home Current 802.11e channel access mechanism Proposed channel access mechanism Proposed text Simulation results Implementation considerations Conclusions Todor Cooklev Todor Cooklev

Contention in 802.11 scenarios for digital home May 2006 doc.: IEEE 802.11-06/0657r0 May 2006 Contention in 802.11 scenarios for digital home Many traffic streams anticipated in CE dominated home… HD Video Support for 4-5 HD video streams 100-125Mbps Content: Premium, time-shifted, DVD, personal, Gaming Voice Up to 4 streams with tight delay constraints – low throughput Best-effort Web, file transfer, printing - 10Mbps Contention among equal-priority traffic is an important issue Todor Cooklev Todor Cooklev

Digital home of the future May 2006 doc.: IEEE 802.11-06/0657r0 May 2006 Digital home of the future HD content HDTV HDTV V4 HDTV V3 V2 V1 Live or time-shifted Premium HD content Voice 3-4 Data 2-3 Cable, Satellite STB / PVR Media PC over WLAN Internet, IPTV Personal content V5 Todor Cooklev Todor Cooklev

802.11e channel access mechanism May 2006 doc.: IEEE 802.11-06/0657r0 May 2006 802.11e channel access mechanism Fig.1 EDCA channel access mechanism Arbitration inter-frame space (AIFS) is one of the EDCA parameters used to ensure traffic differentiation Each AC has fixed AIFS duration associated with it. The smaller the AIFS the higher the medium access priority But multiple streams of the same AC use same AIFSN leading to increased collision! Fig. 2 From Table 20.2 of 11e Todor Cooklev Todor Cooklev

Proposed channel access mechanism May 2006 doc.: IEEE 802.11-06/0657r0 May 2006 Proposed channel access mechanism Fig. 3 Proposed channel access mechanism Proposed Mechanism AIFSN is random with a certain probability density function For example the distribution can be uniform Fig. 4 Proposed medium access control logic Advantages Possible to assign the ACs a non-integer AIFSN value on an average Less collisions within an AC; higher throughput Todor Cooklev Todor Cooklev

Proposed Text : Section 9.2.3.4 May 2006 doc.: IEEE 802.11-06/0657r0 May 2006 Proposed Text : Section 9.2.3.4 Original… A Non-AP QSTA computes the time periods for each AIFS[AC] from the dot11EDCATableAIFSN attributes in the MIB. QSTAs update their dot11EDCATableAIFSN values using information in the most recent EDCA Parameter Set element of Beacons received from the QAP of the QBSS (see 7.3.2.14). A QAP computes the time periods for each AIFS[AC] from the dot11QAPEDCATableAIFSN attributes in its MIB. NEW… Non-AP QSTA compute AIFSN[AC] using some probability density function over a finite interval. This interval is bounded on one side by the default values in Table 20.2. The other limit of this interval is from the dot11EDCATableAIFSN attributes in the MIB. QSTAs update their dot11EDCATableAIFSN values using information in the most recent EDCA Parameter Set element of Beacons received from the QAP of the QBSS (see 7.3.2.14). Todor Cooklev Todor Cooklev

Proposed Text : Section 9.9.1.3 May 2006 doc.: IEEE 802.11-06/0657r0 May 2006 Proposed Text : Section 9.9.1.3 Original … The value of AIFSN[AC] shall be greater than or equal to 2 for non-AP QSTAs and is advertised by the QAP in the EDCA Parameter Set Information Element in Beacons and Probe Response frames transmitted by the QAP. The value of AIFSN[AC] shall be greater than or equal to 1 for QAPs. NEW… QSTAs select the value of AIFSN according to some probability density function (PDF) over a finite interval. One of these limits (either the lower or the upper limit) is the default value specified in Table 20.2. The other limit is in the dot11EDCATableAIFSN attribute in the MIB. Any PDF is acceptable, including a PDF where QSTA always select one number that belongs to this interval. The limit value AIFSN[AC] is advertised by the QAP in the EDCA Parameter Set Information Element in Beacons and Probe Response frames transmitted by the QAP. If this limit value is smaller than the default values in Table 20.2, then it becomes the lower bound of the interval. If this limit value is higher than the default values in Table 20.2, then it becomes the higher bound of the interval. Todor Cooklev Todor Cooklev

AIFSN intervals per AC May 2006 The limit value specified by the AP could be higher or lower Todor Cooklev

Simulation results with random AIFSN May 2006 doc.: IEEE 802.11-06/0657r0 May 2006 Simulation results with random AIFSN Simulation Parameters 54 Mbps PHY, 12 nodes – 4 BE, 4 Video and 4 Voice AIFSN[AC1] – fixed default values as in Table 20.2, except for video; AIFSN for video is random with uniform distribution over [2 4]. Global Throughput per AC Global Delay per AC Todor Cooklev Todor Cooklev

Implementation Issues May 2006 doc.: IEEE 802.11-06/0657r0 May 2006 Implementation Issues The suggested operation is mandatory, so that it will not get advertised in beacons and probe responses. Since any probability density function is acceptable, all current implementations using fixed AIFSN comply with this proposal, i.e. no change is necessary. Those that do want to change and implement, for example, uniform probability density function, will not only see an improvement in their throughput, but will improve overall network performance. Fairness? The improvement according to the proposed scheme does not come at the expense of degradation somewhere else. The performance of the entire network is improved. Todor Cooklev Todor Cooklev

May 2006 doc.: IEEE 802.11-06/0657r0 May 2006 Conclusions Contention in wireless home scenarios is significant for equal-priority streams The proposed random-AIFSN has benefit to all traffic classes – throughput increases and delay decreases While the proposal is to make the suggested scheme mandatory, in reality it is optional because all current implementations comply with it. Todor Cooklev Todor Cooklev