reconsidering reliable transport protocol in heterogeneous wireless networks wang yang tsinghua...

Reconsidering Reliable Transport Protocol in Heterogeneous Wireless

Networks Wang Yang

Tsinghua University

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Outline

• Background• Concurrent Multipath Transfer• key technologies• Evaluation• Conclusion

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Background- Heterogeneous Wireless Networks

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Background

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

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Paradigm shift -Concurent Multipath Transfer

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Current transport layer approaches

• SCTP (Stream Control Transport Protocol)– Motivation: Transport of

PSTN signaling across the IP network

– Support Multi-Homing: Primary/Backup Link

Concurrent Multipath Transfer

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key technologies

• Connection Management• Striping Policy• Multipath Congestion Control• Buffer Management

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key technologies (1)

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Connection Management

Path Quality Metrics

• CWND• Bandwidth

• Round Trip Time • Loss rate

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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

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key technologies (2)

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Striping Policy

Striping policy

• Proportional to path quality metrics– Cwnd– Bandwidth– RTT– Combinations of above metrics

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key technologies (3)

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Multipath Congestion Control

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

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Design issues

• SACK and cwnd update for each path• Retransmission policies

– Same as originally– Available cwnd space– Least loss rate– Least round trip time

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key technologies (4)

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Buffer Management

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

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Design issues

• Shared rbuf or separated rbuf for each path• Buffer size

– f(loss rate, RTT)– Bandwidth delay product

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Evaluation

• Metrics– Throughput– End-to-end delay– Utilization– Fairness

• Tradeoff between– Throughput vs. delay– Utilization vs. fairness

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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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