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Reconsidering Reliable Transport Protocol in Heterogeneous Wireless Networks

Reconsidering Reliable Transport Protocol in Heterogeneous Wireless Networks. Wang Yang Tsinghua University. Outline. Background Concurrent Multipath Transfer key technologies Evaluation Conclusion. Background - Heterogeneous Wireless Networks. Background.

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Reconsidering Reliable Transport Protocol in Heterogeneous Wireless Networks

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  1. Reconsidering Reliable Transport Protocol in Heterogeneous Wireless Networks Wang Yang Tsinghua University

  2. Outline • Background • Concurrent Multipath Transfer • key technologies • Evaluation • Conclusion

  3. Background- Heterogeneous Wireless Networks

  4. Background • Utilize Heterogeneous Wireless Networks to satisfy applications’ requirement for • Availability • Bandwidth • Real-time • …

  5. Paradigm shift-Concurent Multipath Transfer

  6. Current transport layer approaches • SCTP (Stream Control Transport Protocol) • Motivation: Transport of PSTN signaling across the IP network • Support Multi-Homing: Primary/Backup Link

  7. Concurrent Multipath Transfer 3 3 3 2 2 2 1 1 1 3 3 3 2 2 2 1 1 1

  8. key technologies • Connection Management • Striping Policy • Multipath Congestion Control • Buffer Management

  9. key technologies (1) Connection Management

  10. Path Quality Metrics • CWND • Bandwidth • Round Trip Time • Loss rate

  11. Design Issues • Tradeoff between freshness and cost • Time invariant wireless link • Link monitoring • network or host based • Cross-layer design • Leverage MAC/PHY layer information

  12. key technologies (2) Striping Policy

  13. Striping policy • Proportional to path quality metrics • Cwnd • Bandwidth • RTT • Combinations of above metrics

  14. key technologies (3) Multipath Congestion Control

  15. Packets Out of order • Assumption for TCP congestion control • Wired link: out of order implies congestion • Wireless link: out of order implies congestion or loss • Don’t apply to concurrent multipath transfer • Conventional wisdom leads to • Spurious Retransmission • Conservative cwnd growth • Increased ack traffic

  16. Design issues • SACK and cwnd update for each path • Retransmission policies • Same as originally • Available cwnd space • Least loss rate • Least round trip time

  17. key technologies (4) BufferManagement

  18. Receiver Buffer Blocking • TCP Buffer tuning • Suggest buffer size: bandwidth delay product • In concurrent multipath transfer with shared rbuf • bandwidth delay product varying -> rbuf blocking -> spurious retransmission -> throughput degradation

  19. Design issues • Shared rbuf or separated rbuf for each path • Buffer size • f(loss rate, RTT) • Bandwidth delay product

  20. Evaluation • Metrics • Throughput • End-to-end delay • Utilization • Fairness • Tradeoff between • Throughput vs. delay • Utilization vs. fairness

  21. Conclusions • Heterogeneous Wireless Networks is coming as future generation wireless networks • Concurrent Multipath transfer possible answers new application requirements • Key technologies for concurrent multipath transfer • Evaluation of solution space is expected as future work

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