210 likes | 333 Views
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.
E N D
Reconsidering Reliable Transport Protocol in Heterogeneous Wireless Networks Wang Yang Tsinghua University
Outline • Background • Concurrent Multipath Transfer • key technologies • Evaluation • Conclusion
Background • Utilize Heterogeneous Wireless Networks to satisfy applications’ requirement for • Availability • Bandwidth • Real-time • …
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 3 3 3 2 2 2 1 1 1 3 3 3 2 2 2 1 1 1
key technologies • Connection Management • Striping Policy • Multipath Congestion Control • Buffer Management
key technologies (1) Connection Management
Path Quality Metrics • CWND • Bandwidth • Round Trip Time • Loss rate
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
key technologies (2) Striping Policy
Striping policy • Proportional to path quality metrics • Cwnd • Bandwidth • RTT • Combinations of above metrics
key technologies (3) 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
Design issues • SACK and cwnd update for each path • Retransmission policies • Same as originally • Available cwnd space • Least loss rate • Least round trip time
key technologies (4) BufferManagement
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
Design issues • Shared rbuf or separated rbuf for each path • Buffer size • f(loss rate, RTT) • Bandwidth delay product
Evaluation • Metrics • Throughput • End-to-end delay • Utilization • Fairness • Tradeoff between • Throughput vs. delay • Utilization vs. fairness
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