1. 802.11 Multicast Enhancements for Multimedia Streaming
Date:
Notice: This document has been prepared to assist IEEE 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
Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures < 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 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 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at
Pankratov Denis, LG Electronics

2. Multicast-based applications
Real-time video/audio streams
Video conferencing TV
Radio broadcasting
Gaming
etc.
Pankratov Denis, LG Electronics

3. Problems of IEEE 802.11 multicasting for multimedia streaming
Excessive delay due to recipients operating in Power Save Mode
Unreliability due to absence of any feedback from the recipients
No rate adaptation. Due to unreliability, multicast traffic is transmitted at a lowest Data Rate only. A mechanism is needed to extend optionally the set of Data Rates allowable for multicasting
Pankratov Denis, LG Electronics

4. Excessive delay: Motivation
Multicast audio/video streams are very sensitive to delays (~1-10 ms per frame for audio, 33 ms per frame for video)
According to IEEE rules ( ), multicast frames can be transmitted after DTIM only (delay is not less than 100 ms !!!), because some of recipients may be in Power Save Mode (PSM)
We need to overcome the DTIM boundary and force the recipients to awake and receive the particular multicast multimedia stream more often if it is needed to meet QoS
Pankratov Denis, LG Electronics

5. Scheduled Multicast
If there are one or several multicast recipients of the incoming multicast stream, associated with AP, the AP transmits the special ADDTS Announcement frame(s) just after the next DTIM
ADDTS Announcement is a QoS Action frame (similar to ADDTS Request and ADDTS Response) transmitted by the AP in multicast manner with a specific multicast MAC address (MA)
ADDTS Announcement frame includes TSPEC, TCLAS, Schedule IEs, which characterize the particular multicast stream
Pankratov Denis, LG Electronics

6. Scheduled Multicast
All QSTAs receive ADDTS Announcement , because they are not in doze state after DTIM
Every QSTA, which belongs to the particular Multicast Group MA, processes the ADDTS Announcement frame and thus becomes aware of TSPEC, TCLAS and Schedule of the related multicast stream
Using the information from these IEs multicast recipients become awake in time using Scheduled APSD scheme
Pankratov Denis, LG Electronics

7. Scheduled Multicast Diagram
Pankratov Denis, LG Electronics

8. Unreliability: Motivation
Multicast audio/video streams are sensitive to high Packet Loss Ratio values
According to IEEE rules (see 9.2.7), multicast frames can not be acknowledged by any of the recipients and retransmitted. So, there is no MAC-layer recovery on broadcast and multicast frames and Packet Loss Ratio can be intolerably high
We need to propose a scheme with feedback messages from the recipients indicated the necessity of additional retransmission(s), etc.
Pankratov Denis, LG Electronics

9. Scheduled Multicast with Feedback
AP receives feedback message(s) from the recipient(s)
AP may change the stream transmission schedule by including or excluding additional retransmission, taking into account the received feedback messages
In case of the change, AP transmits the next ADDTS Announcement frame(s) after the next DTIM with a modified TSPEC and Schedule IEs
AP transmits the multicast packets according to the new schedule
Pankratov Denis, LG Electronics

10. Rate adaptation: Motivation
Multicast video streams are very bandwidth consuming (~ up to 1-2 Mbps for HD video at application layer)
According to IEEE rules (see 9.2.7), multicast frames can not be acknowledged by any of the recipients and thus, AP can not make a decision which rate to use for multicasting. Thus, multicast traffic is transmitted at the most robust and lowest Data Rate
We need to propose a scheme which can adaptively adjust the Data Rate for the multicast stream if it is necessary
Pankratov Denis, LG Electronics

11. Scheduled Multicast with Rate Adaptation
AP receives feedback message(s) from the recipient(s)
AP may decide to increase or to decrease the Data Rate for the particular multicast stream, using the information from received feedback messages
AP transmits the ADDTS Announcement frame after the next DTIM at the modified Data Rate and with modified Schedule IE and TSPEC IE
AP transmits the multicast packets of the multicast stream at the modified Data Rate according to the new schedule
Pankratov Denis, LG Electronics

12. Call for interest
Who’s interested in getting together to work on this?
Scheduled Multicast
Scheduled Multicast with Feedback
Scheduled Multicast with Rate Adaptation
Pankratov Denis, LG Electronics