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IEEE 802.11aa: Improvements on video transmission over Wireless LANs

IEEE 802.11aa: Improvements on video transmission over Wireless LANs. Speaker : Song- Ferng Wang Advisor : Dr . Ho-Ting Wu Date : 2014/1/6. Outline. Introduction IEEE 802.11 multicast issues IEEE 802.11e EDCA IEEE 802.11aa Conclusions References. Introduction.

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IEEE 802.11aa: Improvements on video transmission over Wireless LANs

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  1. IEEE 802.11aa: Improvements on video transmission over Wireless LANs Speaker : Song-FerngWang Advisor : Dr. Ho-Ting Wu Date : 2014/1/6

  2. Outline • Introduction • IEEE 802.11 multicast issues • IEEE 802.11e EDCA • IEEE 802.11aa • Conclusions • References

  3. Introduction • Video applications are rapidly becoming the main source of traffic in the Internet. With the presence of IEEE 802.11 networks constantly expanding, and the growing use of mobile devices with high computational power and display capabilities.

  4. Introduction • The first IEEE 802.11 wireless LAN standards were unable to handle efficient video transmission since the bandwidth was too small for the demands of video applications and they could only support a best-effort service which is unacceptable for the QoS restraints of video transmission

  5. Introduction • The multicast mechanism provided by the legacy IEEE 802.11 is unreliable and cannot offer the necessary QoS for transmitting video streams • multicast communication in IEEE 802.11 wireless LANs suffers from many problems.

  6. IEEE 802.11 multicast issues (1) • the MAC layer of IEEE 802.11 networks specifies that multicast frames can only be transmitted using the Basic Access scheme. Therefore, it cannot use the RTS/CTS mechanism to protect broadcasting of the frame.means that multicast transmission is unreliable • issues about the scheduling and synchronization of receiving them

  7. IEEE 802.11 multicast issues (2) • IEEE 802.11 MAC specifies that multicast frames must be transmitted using one of the bit rates specified in the Basic Rate Set (BRS), which is a minimum set of bit rates that must be supported by all stations in a IEEE 802.11 wireless LAN to ensure that they can receive control frames.

  8. IEEE 802.11aa • Compatibility with the relevant mechanisms defined by IEEE 802.1AVB (802.1Qat, 802.1Qav, 802.1AS) for multimedia stream transport. • To allow video streams to degrade in a graceful manner when the channel capacity is insufficient , by enabling packet discarding without any requirement for deep packet inspection.

  9. IEEE 802.11aa • The ability to prioritize between different video transport streams that belong in the same EDCA Access Category. • Stream Classification Service (SCS) • A method for mitigating the effects of overlapping BSS environments to offer increased robustness , without the need for centralized management.

  10. IEEE 802.11aa • Improvement for the multicast/broadcast mechanism of IEEE 802.11 in order to offer better link reliability and low jitter characteristics. • 802.11v Directed Multicast Service • Groupcast with Retries (GCR) Unsolicited Retries • Groupcastwith Retries (GCR) BlockAck

  11. 802.11v Directed Multicast Service • converts multicast traffic to unicast frames directed to each of the group recipients in a series. The transmission uses the normal acknowledgement policy and will be retransmitted until it is received correctly.

  12. Groupcast with Retries (GCR) Unsolicited Retries • This mechanism allows the transmission of the multicast frames to be repeated a number of times.

  13. Groupcast with Retries (GCR) BlockAck • This method extends the BlockAck mechanism specified in IEEE 802.11n for use in multicast transmissions to a group. • The AP transmits a number of multicast frames and then requests from one or more of the recipients to acknowledge the receipt of the transmitted frames. Frames that have not been received correctly by one or more of the receivers can then be retransmitted.

  14. IEEE 802.11 DCF • DCF (Distributed Coordination Function)為基本通道存取機制，通訊台(Station, STA)利用載波偵測多重存取/碰撞避免通訊協定(Carrier-Sense Multiple Access/Collision Avoidance, CSMA/CA)來競爭通道使用權。通訊台在準備傳送訊框之前，必須使用載波偵測監測通道情況，確定通道為閒置狀態後才開始準備傳送資料，以避免通訊台之間強行傳送訊框而發生碰撞情況。

  15. IEEE 802.11 DCF

  16. IEEE 802.11e EDCA • EDCA function in IEEE 802.11e to provide Quality of Service for video and voice streams specifies Access Categories (AC) with different priorities • 8 Traffic Category (TC) • 4 Access Category(AC)

  17. IEEE 802.11e EDCA

  18. IEEE 802.11e EDCA

  19. Stream Classification Service (SCS) • The IEEE 802.11aa amendment aims to increase the granularity of the EDCA access categories to allow for prioritization between different video streams.

  20. Stream Classification Service (SCS)

  21. Conclusions • The IEEE 802.11aa amendment provides a foundation for video stream transport over IEEE 802.11 wireless LANs. It provides a set of mechanisms such as the multiple multicast policies, the Stream Classification Service and the QLoad information element, but the use of them is open to the implementation. The choice of the appropriate mechanism, depending on the situation and the setting of its parameters, is an issue of great interest for future research.

  22. References • Kostas Maraslis, PeriklisChatzimisios and Anthony Boucouvalas,“IEEE 802.11aa: Improvements on video transmission over Wireless LANs”, Communications (ICC), 2012 IEEE International Conference on Ad-hoc and Sensor Networking Symposium, pp. 115-119, June 2012 • 林佳慧，“以動態競爭視窗調整機制改善無線區域網路IEEE 802.11e規格之效能”，碩士論文，台北科技大學，May 2008

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