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July 2005 doc.: IEEE 802.11-05/0632r1 802.11 MAC extensions for high rate Video Date: 2005-07-17 Authors: Name Company Address Phone email Clifford Tavares Hitachi America 2000 Sierra Point 408-718-5260 Ltd. Parkway, MS 600 Clifford.Tavares@ Brisbane CA 94005 hal.hitachi.com Todor Cooklev Consultant 121 Miramonte Dr. 925-377-6700 firstname.lastname@example.org Moraga CA 94556 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. 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If you have questions, contact the IEEE Patent Committee Administrator at <firstname.lastname@example.org>. Submission Slide 1 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 Abstract In this presentation we identify the requirements for video transmission over 802.11 networks. We come to the conclusion that the recently completed 802.11e amendment for QoS appears to be inadequate for end- to-end QoS for high quality video over 802.11. We survey work done at other organizations such as the IETF. Some MAC-level solutions to the end-to-end QoS problems are outlined. These solutions require further standardization work beyond 802.11e. Submission Slide 2 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 Outline • 802.11e and its limitations • Potential solutions to the 802.11e limitations • Current work in media-independent and media- dependent packet-based FEC • Relevant work at IETF • Conclusions Submission Slide 3 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 802.11e and its limitations • 802.11e is an almost complete “QoS amendment” • Priorities are assigned only within a session • There is no prioritization of traffic ‘within’ an AV stream • Current prioritization provides latency and average throughput enhancement • Scheduling and admission control are still largely left to vendors • Different applications have specific jitter, latency and retransmission requirements. They are still not part of TSPEC Submission Slide 4 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 Potential MAC-level solutions • Truly dynamic prioritization • Operational profile (TSPEC) may be developed for standard DLNA formats • Admission control and scheduling schemes should be standardized for AV clients • Jitter requirements should be specified in the TSPEC together with block ACK length, retransmissions, and aggregation size. • Content specific dynamic link rate adaptation may be specified • A separate direct link transmission mode may be defined for hi-speed transmission of video Submission Slide 5 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 Potential solutions to the limitations of 802.11e (cont.) • Two-dimensional QoS model – Priority is one dimension – PER is another dimension • This two-dimensional model requires media-specific methods Submission Slide 6 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 End-to-end QoS support for multimedia over 802.11 • Media-specific – Packets belonging to one media class can be assigned different priorities depending on each packet’s contribution to overall QoS – Adjust FEC and power control depending on media type and class • An adaptive MAC is necessary to determine the resources (throughput and battery power) for multimedia delivery. Submission Slide 7 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 MAC enhancements for multimedia over 802.11 • Adaptive congestion control – Reduce packet loss and delay – Rate control and rate adaptive encoding • MAC-level FEC Submission Slide 8 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 Media Independent FEC • Given k data packets • Generate n-k parity packets • Transmit n packets • Any subset of k received packets suffices to reconstruct the data. The exact position of missing packets is unknown. • IETF RFC 2733: An RTP Payload Format for Generic Forward Error Correction Submission Slide 9 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 Media-independent FEC advantages and disadvantages • Advantages – it is media independent – Efficient for multicast • Disadvantages: – Delay is increased (up to n packets) – Decoder complexity – Relationship between FEC and congestion control generally not very well understood Submission Slide 10 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 Media-specific FEC • Send a lower-resolution redundant packet • Advantages: – Low latency – Less redundancy • Disadvantage – Lower quality – Decoder complexity Submission Slide 11 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 Priority Encoding Transmission • Specify different priorities for different data segments • According to assigned priority use different FEC • Early detection of packet loss is the key Submission Slide 12 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 Hybrid error control (ARQ/FEC) • How do you choose the right amount of redundancy? • Hybrid error conrtol – No redundancy after the first transmission – Redundant packets are sent afterwards • Efficient for multicast • Further research is necessary Submission Slide 13 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 Relevant prior work • RTP: Transport protocol for real-time applications: IETF RFC 1889 – Source identification – Packet loss detection – Inter-media synchronization – Intra-media synchronization • RTCP: RTP plus periodic retransmission of control packets Submission Slide 14 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 Conclusions • 802.11e provides basic QoS, but is inadequate for high end multimedia applications • More work is carried out by IETF and others • Further MAC-level solutions are necessary – Dynamic prioritization – Generalized TSPEC – Content-specific techniques Submission Slide 15 Clifford Tavares, Hitachi America Ltd. July 2005 doc.: IEEE 802.11-05/0632r1 References • J. Kowalski, “Link measurement results give thumbs-up to MAC FEC,” doc. 802.11-01/422r0, July 2001. • S. Choi, “New OFDM SERVICE field format for .11e MAC FEC,” doc. 802.11-02/051r0, January 2002. • C. Padhye, K. Christensen, and W. Moreno, “A new adaptive FEC loss control algorithm for voice over IP applications,” IEEE Performance Computing and Communications Conf., Feb. 2000 • Q. Zhang, W. Zhu, Y.-Q. Zhang, “End-to-end QoS for video delivery over wireless Internet,” Proc. IEEE, vol. 93, pp. 123-134, Jan. 2005. • S. Choi, “IEEE 802.11e MAC-level performance evaluation and enhancement, IEEE Globecom 2002. Submission Slide 16 Clifford Tavares, Hitachi America Ltd.
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