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Leveraging Multiple Network Interfaces for Improved TCP Throughput

Leveraging Multiple Network Interfaces for Improved TCP Throughput. Sridhar Machiraju, Prof. Randy Katz. Motivation. Proliferation of Wireless LANs, rollout of 3G and availability of devices with multiple network interfaces (MNIs) Can endhosts leverage multiple network interfaces for –

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Leveraging Multiple Network Interfaces for Improved TCP Throughput

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  1. Leveraging Multiple Network Interfaces for Improved TCP Throughput Sridhar Machiraju, Prof. Randy Katz

  2. Motivation • Proliferation of Wireless LANs, rollout of 3G and availability of devices with multiple network interfaces (MNIs) • Can endhosts leverage multiple network interfaces for – • improved throughput (our current focus) • masking packet losses • improving connectivity …

  3. Problem Statement N3 2 Mbps, 50ms 2 Mbps, 50ms (Sender) N1 N2 (Receiver) 5 Mbps, 50ms 5 Mbps, 100ms N4 • FTP Source N1 has 2 NIs • The 2 paths to N2 are using N3 (2Mbps, 100ms) and N4 (5Mbps, 150ms) • Can N1 obtain a throughput of 7Mbps?

  4. A Simple RR Scheme • Assume that the ratio of bottlenecks on both paths is known (2:5 in the figure) • Route 2 of every 7 packets through N4 and the rest through N3 • Notice that the throughput is less than what is obtained from even one path Throughput Time

  5. Why it fails… • The RR scheme fails - different delays on paths-> packet reordering-> duplicate ACKs -> false congestion signals • Reordering can be solved by – • Increasing DupACK threshold • Buffering packets/ACKs • Our solution – use multiple paths to the source in an intelligent fashion

  6. DupACK routing policy RP1 FP1 (Sender) N1 N2(Receiver) If DupACK, route through RP1 else use RP2 FP2 RP2 • Assume 2 paths are (delayFP1 < delayFP2) such that (delayFP2+delayRP1) < (delayFP1+delayRP2) (delay property) • DupACKs received only after subsequent ACKs and are discarded

  7. DupACK routing policy (cont.) • Single TCP flow is able to obtain better throughput – 7Mbps Throughput Time • Cons – • 2 paths need to obey the delay property • slower increase of congestion window • Pros – • better throughput • simple policy • packets not buffered or dropped

  8. ACK Routing Policy P1 (Sender) N1 N2(Receiver) Route ACKs through P1 P2 • What if DupACK policy cannot be used? • Throughput can still be improved if • delay(P1) < delay(P2) • capacity (P1) > ACK traffic • Use high capacity path (P2) for data; low delay path (P1) for ACKs

  9. ACK Routing Policy (cont.) • Among competing TCP flows, flows with smaller RTT fare better • Using our policy, RTT can be reduced Throughput Time Time Competing TCP Multipath TCP

  10. Future Work • Investigate the effect of competing TCP flows on such policies • Devise more mechanisms esp. for other transport protocols • Infer path properties dynamically • Investigate approaches to deployment – • receiver side modification • use mobility servers such as home agents • Finally, implement these

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