1 / 21

TCP-LP: A Distributed Algorithm for Low Priority Data Transfer

TCP-LP: A Distributed Algorithm for Low Priority Data Transfer. Aleksandar Kuzmanovic & Edward W. Knightly. Rice Networks Group http://www.ece.rice.edu/networks. Motivation. Traditional view of service differentiation: High priority: real-time service Best-effort: everything else

claire
Download Presentation

TCP-LP: A Distributed Algorithm for Low Priority Data Transfer

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. TCP-LP: A Distributed Algorithm for Low Priority Data Transfer Aleksandar Kuzmanovic & Edward W. Knightly Rice Networks Group http://www.ece.rice.edu/networks

  2. Motivation • Traditional view of service differentiation: • High priority: real-time service • Best-effort: everything else • What’s missing? • Low-priority (receiving only excess bandwidth) • Lower than best-effort! • Non-interactive apps, bulk download • Speeds up best-effort service • Inference of available bandwidth for resource selection • Routers could achieve via a low (strict) priority queue • Objective: realize low-priority via end-point control • Premise: routers will not help

  3. Applications for Low Priority Service • LP vs. rate-limiting: • P2P file sharing • Often rate limited • Isolation vs. sharing • LP vs. fair-share: • Bulk downloads • Improve my other applications • Data-base replication across the Internet

  4. Problem Formulation & Design Objectives • Low-priority service objectives • Utilize the “excess/available” capacity • What no other flows are using • TCP-transparency (non-intrusiveness) • Inter-LP flow fairness (fair-share of the available bandwidth)

  5. Origins of the Available Bandwidth • Why is excess bandwidth available when TCP is greedy? • TCP is imperfect • Cross-traffic burstiness • Delayed ACKs due to reverse traffic frees up available bandwidth • Short-lived flows • Majority of traffic consists of short-lived flows (web browsing) • Bandwidth gaps between short lived-flows

  6. Illustration of TCP Transparency • LP flow utilizes only excess bandwidth • Does not reduce the throughput of TCP flows

  7. How Is This Different from TCP? • In presence of TCP cross-traffic: • TCP achieves fairness • LP achieves TCP-transparency

  8. Fairness Among LP Flows • Inter-LP-fairness is essential for simultaneous • file transfers • estimates of available bandwidth

  9. TCP-LP:A Congestion Control Protocol • Key concepts • Early congestion indication • One-way delay thresholds • Modified congestion avoidance policy • Less aggressive than TCP Implication: Sender-side modification of TCP incrementally deployable and easy to implement

  10. Early Congestion Indication • For transparency, TCP-LP must know of congestion before TCP • Idealized objective: buffer threshold indication • Endpoint inference: one-way delay threshold • RFC1323 • Source - destination time stamping • Synchronized clocks not needed • Eliminates bias due to reverse traffic

  11. TCP-LP Congestion Avoidance • Objectives: LP-flow fairness and TCP transparency • LP-flow fairness • AIMD with early congestion indication • Transparency • Early congestion indication • Inference phase goals: • Infer the cross-traffic • Improve dynamic properties • “MD” not conservative enough

  12. TCP-LP Timeline Illustration - Send 1 pkt/RTT - Ensure available x bandwidth > 0

  13. TCP-LP Timeline Illustration • - AI phase • - CWND/2 upon __early congestion xxindication • - Inference phase

  14. TCP-LP Timeline Illustration • 2nd CI => CWND=1 • - Inference phase

  15. TCP-LP Timeline Illustration

  16. Low-Aggregation Regime • Hypothesis: TCP cannot attain 1.5 Mb/s throughput due to reverse cross-traffic • How much capacity remains and can TCP-LP utilize it?

  17. TCP-LP in Action • TCP alone 745.5 Kb/s • TCP vs. 739.5 Kb/s TCP-LP 109.5 Kb/s TCP-LP is invisible to TCP traffic!

  18. High-Aggregation Regime with Short-Lived Flows • Bulk FTP flow using TCP-LP vs. TCP • Explore delay improvement to web traffic • Explore throughput penalty to FTP/TCP-LP flow

  19. TCP Background Bulk Data Transfer • Web response times are normalized

  20. TCP-LP Background Bulk Data Transfer • Web response times improved 3-5 times • FTP throughput: TCP:58.2% TCP-LP: 55.1%

  21. Conclusions • TCP-LP adds a new service to the Internet • General low priority service (compared to “best-effort”) • TCP-LP is easy to deploy and use • Sender side modification of TCP without changes to routers • TCP-LP is attractive for many applications: ftp, web updates, overlay networks, P2P • Significant benefits for best effort traffic, minimal throughput loss for bulk flows http://www.ece.rice.edu/networks/TCP-LP

More Related