1 / 29

Improving Wireless LAN Performance via Adaptive Local Error Control

Improving Wireless LAN Performance via Adaptive Local Error Control. Presented by Yuanfang Cai. Outline. Local error control introduction Evaluations Simple local error control MAC & LLC design and implementation Experimental approach Results Adaptive local error control

dorjan
Download Presentation

Improving Wireless LAN Performance via Adaptive Local Error Control

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. Improving Wireless LAN Performance via Adaptive Local Error Control Presented by Yuanfang Cai

  2. Outline • Local error control introduction • Evaluations • Simple local error control • MAC & LLC design and implementation • Experimental approach • Results • Adaptive local error control • MAC & LLC design and implementation • Experimental approach • Results • Summary

  3. Local versus End-to-end Error Control • Attractions: • Understand local characteristics • More efficient • Easier to deploy • Problems: • Confusing higher layer protocols • Undesirable interaction • Wasted Effort

  4. Design Tradeoffs for Local Error Control • Hardware error control • Simple • Can not differentiate flows • “Pure” link-layer approaches • Per-packet basis • Flow-aware • “Protocol-aware” link-layer protocols • Requires gateways to understand a wide variety of protocols. • “Gateway-style”/”indirect” error control • Might have to understand multiple protocols • Routing changes

  5. Simple local error control • MAC design • Master/slave transactions • INVITE and JOIN • POLL-DATA and DATA-ACK • LLC design • Entirely lost, partially lost, corrupted • Stop-and-wait retransmission

  6. Simple local error control—MAC and LLC design

  7. Simple local error control—Implementation and Performance • Intel 80486 and Pentium laptops using 915 MHz PCMCIA card WaveLAN units • NetBSD Unix • 43% throughput loss

  8. Simple local error control--Experimental Approach Single Hop Ethernet + wireless WAN extension Client: 75 MHz Pentium Toshiba Satellite pro 400CDT Wireless Host Basestation 25 MHz 80486 DEC pc-4255SL

  9. Evaluation—Pure local error control • Pattern-based evaluation • Packet killer • Basic robust evaluation • TCP without local error control • TCP with local error control • Broader scenarios • Ethernet + wireless • WAN extension • Competing TCP streams

  10. TCP without local error control

  11. TCP without local error control

  12. TCP with local error control

  13. TCP with local error control

  14. Ethernet + wireless

  15. WAN extension

  16. Competing TCP streams

  17. Simple local error control--Analysis • Steady state conditions (Assume that TCP is stable) • Lost packets always indicate congestion. • Avoid packet reordering • Don’t have long delay • Dynamic error environment • Upgrade • Degrade

  18. Simple local error control--Analysis • Persistence of local error control • Perpetual retransmission • Give up after a few transmissions • The higher error environment, the more persistent the retransmission need to be. • Packet Delay by persistent local retransmission

  19. Simple local error control--Analysis

  20. Simple local error control--Analysis

  21. Simple local error control--Analysis

  22. Simple local error control--Analysis • 3% overlap • End-to-end retransmission timeouts should be substantially longer than the single-hop round-trip time • TCP features that allow persistent retransmission with a small efficiency loss • Delay variation • Cautious minimum timeout • Slow-start probing

  23. Adaptive local error control • LLC Design • Add FEC and packet shrinking • Packet truncation • Rare for short packets • Bit corruption • Have only a few bit errors • Packet Shrinking • Forward Error Correction (FEC) • Reed-Solomon codes • Observe the quality of the link • Tell slaves using POLL-DATA • Employ adaptive policies

  24. Adaptive local error control • LLC Implementation • Implement packet shrinking through packet segmentation and reassembly • Data transmission: • Add to the packet sequence number: • starting byte offset, • a byte count • a packet complete bit • Acknowledgement: • A package sequence number • A cumulative length indicating correctly received bytes • Rare for short packets • Emulates the effects of Forward Error Correction (FEC)

  25. Adaptive local error control • Static Policies • BOLD—Without coding or shrinking • LIGHT—5% coding overhead • Robust—Sends minimally-sized packets with nearly 1/3 of each devoted to coding overhead. • Adaptive policies • BIMODAL • BOLD in good conditions • ROBUST in poor conditions • BI-CODE—BIMODAL that only adjust coding overhead • BI-SIZE—BIMODAL that only adjust coding overhead • FLEX—adapts the packet size and degree of FEC redundancy independently

  26. Adaptive local error control

  27. Adaptive local error control

  28. Adaptive local error control

  29. Summary • “Pure” link-layer local error control mechanism can greatly increase the efficiency of data transfer in wireless LAN’s. • Flow-aware instead of Protocol-aware • Simple adaptive policies outperformed static policies across a range of error environments.

More Related