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A Reliable Multicast for Unidirectional Satellite Link <RMUS> 1 0011 0010 1010 1101 0001 0100 1011 Patcharee Basu, Kanchana Kanchanasut yoo@soi.ne.jp, kk@cs.ait.ac.th intERLab Asian Institute of Technology Objectives 0011 0010 1010

  1. A Reliable Multicast for Unidirectional Satellite Link <RMUS> 1 0011 0010 1010 1101 0001 0100 1011 Patcharee Basu, Kanchana Kanchanasut yoo@soi.ne.jp, kk@cs.ait.ac.th intERLab Asian Institute of Technology

  2. Objectives 0011 0010 1010 1101 0001 0100 1011 • File distribution for Education satellite link – Class materials 1 – Archive lectures • HTML pages • Video files • Image files • Many receivers in rural areas – poor Internet connectivity

  3. Unidirectional satellite link 0011 0010 1010 1101 0001 0100 1011 1 Unidirectional Satellite Link Feed router Receiving routers UDL Receiving networks UDL feeding networks

  4. Unidirectional Link Routing (UDLR) 0011 0010 1010 1101 0001 0100 1011 1 Unidirectional Satellite Link Feed router Receiving routers UDL Receiving networks UDL feeding networks Internet

  5. Satellite UDL & IP Multicast 0011 0010 1010 1101 0001 0100 1011 • Strengthen the broadcasting property • Minimum bandwidth consumption 1 • Used for massive information delivery – Video streaming – Content distribution (Unreliable datagram?)

  6. Concerns 0011 0010 1010 1101 0001 0100 1011 • Application – Need of Reliability – Not time-sensitive • Satellite UDL 1 – Downstream link • High bandwidth • Long delay – Return paths • Receivers do not share the same return path • As good as the worst one – Long delay (Satellite) – Low bandwidth (Dial-up modem)

  7. Reliable Multicast for Unidirectional Satellite Link( RMUS) 0011 0010 1010 1101 0001 0100 1011 • Error Control • Error detection – NAK-based receiver-initiated 1 • Error recovery – Selective repeat • Congestion Control • Congestion Detection – Modification of Monitor-Based Flow Control (MBFC) • Rate adjustment – Congestion management

  8. Error Control(1) 0011 0010 1010 1101 0001 0100 1011 • Error detection – Identification 1 • Receiver (IP, Process ID) • Packet (Sequence Number) – Detection mechanism • Receiver detects the loss • Sender polls for reception results • Receiver reports the reception result back only at the end of the transmission

  9. Error Control(2) 0011 0010 1010 1101 0001 0100 1011 • Error Recovery – Selective repeat 1 • Retransmit only the loss packets – Initiate a new data transmission cycle • Treat the lost packets in the previous cycle as data • Exclude receivers who has completed the transmission – RESENT-RETRY • Current implementation is 10

  10. Error Control RECEIVERS SENDER #1 #2... #N 0011 0010 1010 1101 0001 0100 1011 RQ Queries for receivers Q in u e Send a join message te rytim rv RJ (IP, Process ID) a l e Start data transmission 1 Data transmission End of data transmission POLL_ALL Polling for reception report Q u in Report data loss e te rytim rva or completeion l e Start next session Data Report data loss until all receivers transfer transmission or completeion complete

  11. Congestion Control(1) 0011 0010 1010 1101 0001 0100 1011 • Monitor the network condition – Modification of Monitor based flow control (MBFC), 1 • T. Shiroshita, T. Sano, O. Takahashi, N. Yamanouchi, 1997 • Divide the data transmission into sessions (monitoring region) • Sends a number of packets • Collect reception report from all receivers{NACK or ACK)

  12. Congestion Control(2) 0011 0010 1010 1101 0001 0100 1011 – 2 thresholds for controlling the transmission rate • THup and Thdown 1 If (ACKs/N) > Thup then Increase the rate Else If (NACKs/N) > Thdown then Decrease the rate Else Keep the current rate

  13. RECEIVERS SENDER MBFC #1 #2... #N T MON = ? Send control packet MS 0011 0010 1010 1101 0001 0100 1011 monitor region DATA 1 MS Backoff time ACK or NACK Return reception result monitor region ACK = Complete DATA NACK = Detect Loss Adjust transmission rate and MS continue send next region monitor region ACK or NACK DATA

  14. T MON for UDL T MON = RTT UDL + T BACKOFF 0011 0010 1010 1101 0001 0100 1011 T MON = D UDL + D RTP + T BACKOFF Maximum delay T MON : Time interval of the monitoring region 1 T MON : Time interval of the monitoring region of all return path D UDL : Delay of the unidirectional satellite link = D UDL D UDL : Delay of the unidirectional satellite link D RTP : Delay of the return path D RTP : Delay of the return path T BACKOFF : Backoff timeout to prevent ACK implosion at T BACKOFF : Backoff timeout to prevent ACK implosion at the sender the sender

  15. Rate Adjustment 0011 0010 1010 1101 0001 0100 1011 • Normal network condition(without congestion) – TCP,MBFC : Slow start and Additive increase Initial congestion window = Maximum segment size (MSS) 1 threshold = 64k – Additive increase is too slow for the long RTT network

  16. Rate Adjustment 0011 0010 1010 1101 0001 0100 1011 • Normal network condition(without congestion) – RMUS : slow start and additive increase 1 • Initial congestion window = RMUS segment size(RSS) – In our implementation, RSS= 8*MSS • Threshold is set as RMUS threshold (Rthresh) – In our implementation, Rthresh = 128K

  17. Rate Adjustment 0011 0010 1010 1101 0001 0100 1011 • Congestion case – TCP use multiplicative decrease 1 – RMUS gradually decrease by RSS/2

  18. Scalability 0011 0010 1010 1101 0001 0100 1011 • Backoff timeout – Reduce the density of workload on processing 1 receivers’ requests – Reduce the density of traffic caused by receivers’ messages

  19. Scalability 0011 0010 1010 1101 0001 0100 1011 • Workload of sender ~ Backoff timeout Number of receivers • RMUS with Adaptive Tmon 1 T MON = RTT UDL + T BACKOFF where T BACKOFF = F n ( Number of receivers)

  20. Experiment 0011 0010 1010 1101 0001 0100 1011 • Actual UDL satellite network • Asian Internet Interconnection Initiatives 1 project (www.ai3.net) • 9 Mbps C band satellite link • Feed at Japan • Receivers at Thailand, Indonesia, Japan’s receiving site.

  21. Experiment network ���������� 0011 0010 1010 1101 0001 0100 1011 ������ ���������� ���� ������������� LAN �������������� 1 ������������� ���������� ���������� ���������� ���������� ���������� ���������� ��������

  22. Experiment network 0011 0010 1010 1101 0001 0100 1011 Return path Delay (ms) Receiver 1 LAN 0.119 1 Receiver 2 Bidirectional 270 satellite Receiver 3 Regular Internet 124 Receiver 4 Regular Internet 150

  23. Experimental Variables 0011 0010 1010 1101 0001 0100 1011 RMUS parameter Value TH UP 0.9 1 TH DOWN 0.3 Backoff time 0.3 second

  24. Evaluation 0011 0010 1010 1101 0001 0100 1011 • Comparison of RMUS, MBFC,TCP on – Performance 1 • Transmission rate – Overhead • Amount of overhead on return path

  25. Rate Adjustment 0011 0010 1010 1101 0001 0100 1011 6000 5000 1 4000 Rate (kbps) TCP 3000 MBFC RMUS 2000 1000 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 2 5 7 0 2 5 7 0 2 5 7 0 2 5 7 0 2 5 7 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 Time (second)

  26. RMUS & TCP 0011 0010 1010 1101 0001 0100 1011 6000 5000 1 4000 Rate (kbps) TCP 3000 RMUS 2000 1000 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 4 8 3 7 2 6 1 5 0 4 9 3 8 2 7 1 6 0 5 9 5 9 1 1 2 2 3 3 4 4 5 5 5 6 6 7 7 8 8 9 9 9 Time (second)

  27. MBFC & TCP 0011 0010 1010 1101 0001 0100 1011 1400 1200 1000 1 Rate (Kbps) 800 TCP MBFC 600 400 200 0 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 5 0 5 0 5 5 1 6 2 7 3 8 4 9 5 0 6 1 7 2 8 3 9 4 0 5 1 6 1 1 2 2 3 3 4 4 5 6 6 7 7 8 8 9 9 0 1 1 2 2 1 1 1 1 1 Time (second)

  28. RMUS 2 flows 0011 0010 1010 1101 0001 0100 1011 5000 4500 4000 3500 1 3000 Rate (Kbps) RMUS flow 1 2500 RMUS flow 2 2000 1500 1000 500 0 120 160 200 240 280 320 360 400 440 480 520 560 600 640 680 720 760 800 840 40 80 Time (second)

  29. RMUS 3 flows 0011 0010 1010 1101 0001 0100 1011 ���� ���� ���� 1 ���� Rate (Kbps) ���� ���� ���� ��� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � Time (second)

  30. ���� ���� ���� ���� ���� 0011 0010 1010 1101 0001 0100 1011 ��� � �� �� ��� ��� ��� ��� ��� ��� ��� RMUS 4 flows ��� ��� ��� ��� ��� ��� Time (seond) ��� ��� ��� ��� ��� ��� ��� ���� ���� ���� 1 ���� ���� ���� ���� ���� ���� ���� ���� ����

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