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

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

3. Background - Heterogeneous Wireless Networks 3

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

5. Paradigm shift - Concurent Multipath Transfer 5

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 7 1 2 3 3 1 2 3 3 1 2 3 1 2 3 1 2 1 2

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

9. key technologies (1) 9 Connection Management

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

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 11

12. key technologies (2) 12 Striping Policy

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

14. key technologies (3) 14 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 – Dont apply to concurrent multipath transfer Conventional wisdom leads to – Spurious Retransmission – Conservative cwnd growth – Increased ack traffic 15

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 16

17. key technologies (4) 17 Buffer Management

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 18

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

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

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 21