1 / 29

Deploying Safe User-Level Network Services with icTCP

This paper discusses the icTCP framework, addressing the challenges in deploying modifications to TCP/IP by offering a safe and user-level approach with minimal overhead. The framework enables user-level extensions and provides control to libraries, facilitating deployment and customization. icTCP aims to make TCP modifications more accessible and efficient, enhancing network services. Developed at the Advanced Systems Laboratory, University of Wisconsin - Madison, the framework focuses on information exposure and safe control mechanisms for user libraries.

snarvaez
Download Presentation

Deploying Safe User-Level Network Services with icTCP

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. Deploying Safe User-Level Network Services withicTCP Haryadi S. Gunawi Andrea C. Arpaci-Dusseau Remzi H. Arpaci-Dusseau The ADvanced Systems Laboratory (ADSL) Univ. of Wisconsin - Madison

  2. Motivation • Vast number of proposed modifications to TCP/IP • Some adopted, others not deployed • TCP Vegas [SIGCOMM `94] • TCP Nice [OSDI `02] • Congestion Manager (CM) [SIGCOMM `99] • Heart of deployment problem: OS kernel • OS tend to be substantial and complex • Vendors dislike changing them when benefit is not imminent • A range of OS-es must implement the modifications • Transition of good research ideas into wide-spread use is slow • Emerging different network environments • Wireless (lossy network), Load-balancing (packet reordering) • Different extensions for different network environment • TCP only support some

  3. f( ) f( ) in-kernel extensions Current TCP implementation TCP Applications TCP Reno

  4. Information Control Inside to outside • Why in-kernel extensions? • Information and control only available within the kernel • Ex: TCP Vegas • Information: per-packet RTT and TCP States • Control: Congestion Window • Questions? • Can extensions be built in application layer? • What information and control need to be exposed? TCP Applications TCP f( )

  5. Proposed Framework • icTCP (“information and control” TCP) • Address the problem of deployment • Slightly modified in-kernel TCP stack • Exports key pieces of information • Provides safe control to user-level libraries • Given information and control, extensions can be built in application layer • Evaluation • Converting TCP to icTCP requires a small amount of additional code • The resulting flow is TCP friendly • Minimal overhead • Implement 6 user-level extensions • Little complexity in implementing extensions at user-level

  6. Deployable Flexible Composable Apps Apps App1 App2 lib-f( ) lib-f( ) lib-f lib-g lib-g( ) icTCP icTCP icTCP New services packaged as libraries and easily downloaded. Developers can tailor libraries to the their needs Services are used together for more powerful functionality Benefits • icTCP facilitates the development of user-level extensions

  7. Outline • Motivation and Overview • icTCP Design and Implementation • Information • Control • 5 Axes of Evaluation • Conclusion

  8. icTCP Design • Different TCP connections, different libraries • User-Libraries on top of icTCP • icTCP exposes Information and Control

  9. Information • Which information should be exposed? • Too little  limited extensions • Too much  expanded interface • 2 types of Information: • Variables part of TCP specification (RFC 793) • cwnd, ssthresh • Message list and Ack list • More detailed information • History of recent packets and acknowledgements • Enabled by user-level services to save memory TCP Clients User Libraries

  10. How and when to obtain information? • Polling • BSD socket interfaces • Unnecessary run-time overhead • Kernel-user space copy • When to obtain accurately? • TCP variables are updated: • upon receipt of an ACK • end of a round • Interrupt mechanism • icTCP notifies application when these events happen

  11. Control • Allow internal TCP variables to be externally set in a safe manner • What variables and what values? • TCP-Friendly: don’t harm other competing standard flows • Philosophy: icTCP must be conservative • Control is allowed if not aggressive • Control 10 (virtual) variables that can be safely set TCP Clients User Libraries

  12. Implementation of Safe-Control • Idea: Virtual variables • congestion window (cwnd)  virtual congestion window (vcwnd) • Manipulate policies through virtual variables • TCP Reno keeps running using the original variables • Safe Ranges • Enforce friendliness • 0 ≤ vcwnd ≤ cwnd • Without safe ranges, resulting flows not TCP-friendly • Choosing 10 variables, defining safe-ranges • Check safe-setting theoretically and empirically • Theoretically: Reno equation • congestion window: control how many packets in the network • vcwnd > cwnd : more packets in the network, thus more aggressive • Empirical Prove • Set virtual congestion window outside the safe ranges

  13. Outline • Motivation and Overview • icTCP Design and Implementation • Framework Evaluation • Conclusion

  14. 5 Axes of Evaluation How easy to convert TCP to icTCP? 1 How difficult to develop TCP extensions in this way? 5 2 Is icTCP friendly? 4 3 What types of extension can be built and deployed with icTCP? What are the overheads? Does it scale?

  15. Converting TCP to icTCP 1 TCP to icTCP • icTCP in Linux 2.4.18 • Add 316 lines of code • Non-intrusive modifications

  16. Unconstrained icTCP (allow variable setting to any value) Tuncons Reno Tuncons Runcons: TReno Reno TReno Reno Network Safety: Unconstrained icTCP Friendly? 2 TCP-Friendly: ~ 1 TCP-Unfriendly

  17. Unconstrained icTCP Constrained icTCP (allow variable setting within the safe ranges) . Tcons Reno Tcons Rcons: TReno Reno TReno Reno Network Safety: Constrained icTCP Friendly? 2 TCP-Friendly TCP-Unfriendly • Safety  Safe Ranges are required!

  18. 3 Scalability and Overhead Scale? Overhead? • What is the overhead? Does it scale? • Rate of getting info and setting variables • Different extensions, get/set at different rate • Two factors: • Per-ack or per-round interrupts • Need the message list and ack list • 3 synthetic libraries: • per-ack interrupt • per-round interrupt • per-round interrupt + gets message list

  19. 3 Overhead Scale? Overhead? (96 conns) R1 R2 per-round 12% S per-round + msgList (8 conns) per-ack 30% 12 MB/s per-ack (4 conns) R3 R4 • Noticeable overhead, but not prohibitive

  20. 4 TCP Extensions Range of Extensions? • Range of TCP extensions can be built on top of icTCP • Implement 3 sets case studies (6 extensions): • Congestion window: • TCP Vegas [Brakmo, SIGCOMM ’94] • TCP Nice [Venkataramani, OSDI ’02] • Congestion Manager (CM) [Balakhrisnan, SIGCOMM ’99] • Duplicate threshold • Reordering-Robust Ext [Zhang, ICNP ‘03] • Efficient Fast Retransmit [Tamura, LCN ‘98] • Retransmission Timeout • Eifel RTO [CCR ‘00]

  21. f vcwnd per-round interrupt Vegas vcwnd TCP states msg list 4 User-level TCP Vegas Implementation Range of Extensions? • Using information and control is simple • Complexity is within the algo itself TCP Clients lib-Vegas icTCP TCP Vegas [Brakmo et.al., SIGCOMM ’94]

  22. 4 Does it work? Range of Extensions? • TCP Reno: Send more packets until drop. • TCP Vegas: Maintain the “right” amount of extra data in the network • e.g. keep only 3 packets in the bottleneck queue Reno User-Level Lib. TCP Vegas In-kernel TCP Vegas • Same Behavior

  23. lib-f TCP + f icTCP App1 App2 EFR RR dt < 3 dt > 3 Lossy Network Packet Reordering 4 icTCP Strengths Range of Extensions? • Implement less aggressive TCP variants at user-level • No need to push changes into the kernel • Ideally suited for tuning parameters whose optimal values depend upon the environment • Lossy Network  retransmit faster  Use Efficient Fast Retransmit • Packet reordering  postpone retransmission  Reordering Robust (RR) Extensions • Different environment, opposing solutions • TCP favors one solution • Correcting errors in parameter values • Eifel RTO [CCR ’00]: RTO prediction flaw when RTT drops • In newer Linux version, this prediction flaw is corrected with adding 2 new lines of code • Must wait vendors to correct this flaw

  24. Apps lib-f Set existing variables with limits icTCP Apps lib-f Set existing vars to any values icTCP Enforcer 4 Other approaches Range of Extensions? • Can’t implement all extensions • Only allow 10 existing variables to be set • Conservative: Safety • STP (Self-Spreading Transport Protocols) [SOSP ’03] • Remotely upgrade other’s protocol stack • More TCP extensions can be deployed • Use separate module to enforce friendliness • Why we don’t use enforcer • Drawback: terminate non-conforming flows • icTCP modulates aggressive flows vs.

  25. Ease of Development Difficult Develop? 5 • How difficult to develop TCP extensions in this way? • Complexity at user-level vs. in-kernel 1200(*) 438

  26. Vegas Vegas RR RR Composability Difficult Develop? 5 • Composing multiple libraries • Vegas: good for small bottleneck queues • RR: good for reordering • Environment where both situations exist? • Vegas+RR: Better throughput TCP Clients icTCP

  27. Conclusion • icTCP • Philosophy: Information and Control • Non-intrusive, simple, and TCP-friendly • Systems with icTCP reap benefits of user-level TCP extensions • Change TCP once now, no need to change it later

  28. Questions? The ADvanced Systems Laboratory www.cs.wisc.edu/adsl

  29. Related Work • Mogul et.al. [HotNets-2003] • Arbitrary state setting • Web100 and Net100 • Export a variety of per-connection statistics • Does not ensure network safety • STP [SOSP-2003] • Remotely upgrade other’s protocol stack • Invasive changes to the kernel • Additional machinery to ensure friendliness • InfoTCP/infokernel [SOSP-2003] • icTCP exposes more information • icTCP allows services to directly set cwnd inside of TCP • icTCP allows more variables to be controlled

More Related