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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 tcooklev@ieee.org
                                                      Moraga CA 94556




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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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