Transcript Reconsidering Transport Protocol in Heteregeneous

Reconsidering Reliable Transport
Protocol in Heterogeneous Wireless
Networks
Wang Yang
Tsinghua University
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Outline
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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
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Connection Management
Striping Policy
Multipath Congestion Control
Buffer Management
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key technologies (1)
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)
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)
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)
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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