1. Leader based Multicast
Date:
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Yongho SEOK

2. Yongho SEOK

3. Abstract
This document describes an example of leader-based multicast mechanism.
First, we introduce the problems of the current multicast mechanism.
Second, we describe a specific leader-based multicast mechanism
Third, we evaluate its benefits with experimental results.
At the end of the presentation, there will be a motion to include normative text of this proposal in v draft.
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4. Introduction Increasing quantity of WiFi enabled portable devices
Growing availability of multimedia streaming
Increasing WiFi coverage on public places
The best option: Multicast
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5. <Saturated Condition>
Problem
Current implementation of Multicast: Open Loop Transmission
No CW adaptation
No retransmission
No rate adaptation
Multicast transmission
starts
<Saturated Condition>
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6. <Unsaturated Condition>
Problem
Current implementation of Multicast: Open Loop Transmission
No CW adaptation
No retransmission
No rate adaptation
4th unicast stream
starts
Multicast transmission
starts
<Unsaturated Condition>
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7. Proposed solution Leader-based Multicast: [Kuri and Kasera]
-AP chooses one receiver as the Leader
Leader sends back ACK to the AP
AP performs the backoff whenever ACK is not received
STA1
STA2
STA4
STA3
ACK
STA5[Leader]
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8. Proposed solution Optional Retransmission
Each multicast group has a different retry limit according to the requirement of the multicast application
If the retry limit is set to 0, a retransmission of a multicast frame is not allowed
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9. Proposed solution Optional Retransmission
When a multicast frame is retransmitted, the retransmitted multicast frame has a virtual BSSID
AP:
BSSID = A
Retransmission BSSID = B
STA1
STA2
Retransmitted Multicast MPDU (BSSID = B)
STA4
STA3
Multicast MPDU (BSSID = A)
STA5[Leader]
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10. Proposed solution Optional RTS/CTS exchange AP sends RTS to Leader
Leader sends back CTS to the AP
STA1
STA2
STA4
STA3
CTS
RTS
STA5[Leader]
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11. Proposed solution Leader Election Protocol
-AP chooses one receiver as the Leader
AP sends a Leader Request frame to the Leader
The leader informs AP of its leadership acceptation (or rejection), by sending back to AP a Leader Response frame
AP sends to the previous leader a Leader Release frame to stop acknowledging frames
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12. Proposed solution Leader Election Protocol Leader Selection Algorithm
-It is possible to utilize IEEE v multicast diagnostic capability
E.g.: The station with the highest PER may be selected as the Leader of the group
STA3
STA5[Old Leader]
STA4[New Leader]
STA2
STA1
Leader Response
ACK
STA3
STA5[Old Leader]
STA4[New Leader]
STA2
STA1
Leader Request
ACK
STA3
STA5[Old Leader]
STA4[New Leader]
STA2
STA1
ACK
Leader Release
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13. Experimentation: Controlled conditions
4 Experiments: 5 tests of 5 minutes of VBR video streaming
Legacy Multicast without background traffic
Legacy Multicast with TCP background traffic
Leader based without background traffic.
Leader based with TCP background traffic
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14. Results Video Goodput for both mechanisms Leader based
Legacy Multicast
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15. Conclusion Leader based solution:
Better throughput than Legacy multicast
Can follow the VBR test video requirements
Increases throughput with retransmissions on a loaded network
Low complexity to be implemented
Compatible with legacy station
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16. Motion
Move to include normative text in document v-normative-text-leader-based-multicast.doc into the TGv draft.
Mover: Emily H. Qi
Seconder:
Result:
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17. References
J. Kuri and S.K. Kasera, “Reliable Multicast in Multi-access Wireless LANs,” ACM Wireless Networks, 2001.
D. Dujovne and T. Turletti, “Multicast in WLANs: An Experimental Study,” in ACM MSWiM 2006.
J. Villalon, P. Cuenca, L. Orozco-Barbosa, Y. Seok and T. Turletti, “Cross-Layer Architecture for Adaptive Video Multicast Streaming over Multirate Wireless LANs,” IEEE JSAC, Vol. 25, No. 4, May, 2007.
Y. Seok and T. Turletti, “Practical Rate-Adaptive Multicast Schemes for Multimedia over IEEE WLANs,” INRIA Report,
B. Metzler and E. H. Qi, “A Statistical Method to Leader-Based ACK for Reliable Multicast in WLAN,” INTEL Technical Report.
*the one from MSWiM where the figures are from
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