Reconsidering Reliable Transport Protocol in Heterogeneous Wireless Networks
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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
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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
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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
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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
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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
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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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