1. Leader based Multicast
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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 ( r4) 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 to reduce collisions
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 LBMS Request frame to the Leader
The leader informs AP of its leadership acceptation (or rejection), by sending back to AP a LBMS Response frame
* FBMSID is used in order to identify the multicast stream
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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
STA1
STA2
Leader Response
ACK
Leader Request (G1, G2, G3)
ACK
STA4
(Leader for G1, G2, G3, G4)
STA4
(Leader for G1, G2, G3, G4)
STA3
Leader Request (G4)
ACK
STA5
(New leader for G4)
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13. Proposed solution Optional Block Ack Mechanism (utilizing FBMS)
Multicast receiver sends an unsolicited LBMS response
AP sends back an unsolicited LBMS request to the Multicast Receiver
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14. Proposed solution Optional Block Ack Mechanism
(without utilizing FBMS)
When the AP does not support the FBMS,
Multicast receiver sends an multicast diagnostics report with the LBMS Trigger Code
AP sends back an unsolicited LBMS request to the Multicast Receiver
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15. (b) Without utilizing FBMS
Proposed solution
Optional Block Ack Mechanism
(utilizing FBMS)
(a) Utilizing FBMS
(b) Without utilizing FBMS
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16. 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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17. Results Video Goodput for both mechanisms Leader based
Legacy Multicast
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18. Conclusion Leader based solution:
Provide the fairness between multicast throughput and unicast throughput
Provide the reliability as using the Block Ack mechanism
Reduce network load by adapting PHY rate
Low complexity to be implemented
Compatible with legacy station
Integrated solution of multicast protocols proposed in TGv and TGn
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19. Motion
Move to include normative text in document v-normative-text-leader-based-multicast.doc into the TGv draft.
Mover:
Seconder:
Result:
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20. 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.
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