1. 802.11 for high data rate multimedia transmission
July 2005
doc.: IEEE /0632r0
July 2005
for high data rate multimedia transmission
Date:
Authors:
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Clifford Tavares, Hitachi America Ltd.
Clifford Tavares, Hitachi America Ltd.

2. July 2005
doc.: IEEE /0632r0
July 2005
Abstract
In this presentation we identify the requirements for video transmission over networks. We come to the conclusion that the recently completed e amendment for QoS appears to be inadequate for end-to-end QoS for high quality video over 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 e.
Clifford Tavares, Hitachi America Ltd.
Clifford Tavares, Hitachi America Ltd.

3. Outline 802.11e and its limitations
July 2005
Outline
802.11e and its limitations
Potential solutions to the e limitations
Current work in media-independent and media-dependent packet-based FEC
Relevant work at IETF
Conclusions
Clifford Tavares, Hitachi America Ltd.

4. July 2005
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 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
Clifford Tavares, Hitachi America Ltd.

5. Potential MAC-level solutions
July 2005
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
Clifford Tavares, Hitachi America Ltd.

6. Potential solutions to the limitations of 802.11e (cont.)
July 2005
Potential solutions to the limitations of e (cont.)
Two-dimensional QoS model
Priority is one dimension
PER is another dimension
This two-dimensional model requires media-specific methods
Clifford Tavares, Hitachi America Ltd.

7. End-to-end QoS support for multimedia over 802.11
July 2005
End-to-end QoS support for multimedia over
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.
Clifford Tavares, Hitachi America Ltd.

8. MAC enhancements for multimedia over 802.11
July 2005
MAC enhancements for multimedia over
Adaptive congestion control
Reduce packet loss and delay
Rate control and rate adaptive encoding
MAC-level FEC
Clifford Tavares, Hitachi America Ltd.

9. Media Independent FEC Given k data packets Generate n-k parity packets
July 2005
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
Clifford Tavares, Hitachi America Ltd.

10. Media-independent FEC advantages and disadvantages
July 2005
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
Clifford Tavares, Hitachi America Ltd.

11. Media-specific FEC Send a lower-resolution redundant packet
July 2005
Media-specific FEC
Send a lower-resolution redundant packet
Advantages:
Low latency
Less redundancy
Disadvantage
Lower quality
Decoder complexity
Clifford Tavares, Hitachi America Ltd.

12. Priority Encoding Transmission
July 2005
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
Clifford Tavares, Hitachi America Ltd.

13. Hybrid error control (ARQ/FEC)
July 2005
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
Clifford Tavares, Hitachi America Ltd.

14. July 2005
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
Clifford Tavares, Hitachi America Ltd.

15. July 2005
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
Clifford Tavares, Hitachi America Ltd.

16. July 2005
References
J. Kowalski, “Link measurement results give thumbs-up to MAC FEC,” doc /422r0, July 2001.
S. Choi, “New OFDM SERVICE field format for .11e MAC FEC,” doc /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 , Jan
S. Choi, “IEEE e MAC-level performance evaluation and enhancement, IEEE Globecom 2002.
Clifford Tavares, Hitachi America Ltd.