1 / 13

School of Computing Science Simon Fraser University

School of Computing Science Simon Fraser University CMPT 771/471: Internet Architecture & Protocols TCP-Friendly Transport Protocols. Motivations. Congestion Control Prevents congestive network collapse Improve Quality of Service (QoS) for UDP Control transmission rate

dexter-neal
Download Presentation

School of Computing Science Simon Fraser University

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. School of Computing Science Simon Fraser University CMPT 771/471: Internet Architecture & Protocols TCP-Friendly Transport Protocols

  2. Motivations • Congestion Control • Prevents congestive network collapse • Improve Quality of Service (QoS) for UDP • Control transmission rate • Fair bandwidth utilization • Prevents starvation of TCP traffic • ~95% of Internet traffic are TCP • In short, a TCP-Friendly protocol based on UDP

  3. Approaches • Resources Reservation • Impossible to know exact bandwidth • May leads to over-allocate • Priority Mechanisms • Require supports by path routers • Adaptive Sending Rate • Easy to implement, application level • Can adapt to changes in bandwidth availability • Improve QoS through loss reduction

  4. Adaptive Sending Rate • Congestion Control • Achieved by varying sending rate • 12+ algorithms for calculating transmission rate • Main idea is to use TCP throughput model • All claims to be the most effective • Loss-Delay Based Adjustment Algorithm (LDA) • TCP like approach • Increase sending rate during network under-load • Uses feedback to accurately measure RTT • Intended for video and audio streaming • Network and Operating System Support for Digital Audio and Video (NOSSDAV ‘98)

  5. Loss-Delay Based Adjustment Algorithm • Loss-Delay Based Adjustment Algorithm (LDA) • Start with a small value, 10 kb/s • Additive increase rate (AIR) • If packet drop, back off to initial value (10 kb/s) • Increase until similar rate as TCP • Relies on feedback • Uses Real Time Protocol (RTP) on top of UDP • Feedback contains losses and round-trip time (RTT) • How much to increase? • Bf = bandwidth factor • AIR = initial value (10 kb/s)

  6. Loss-Delay Based Adjustment Algorithm • How do we calculate ? • r = current transmission rate • b = bottleneck bandwidth • Calculating bottleneck bandwidth • b = probe packet size / gap between 2 probe packets • Two sequential packets with small gap means less delay

  7. Understanding TCP • Detecting Congestion • Recall TCP average throughput • Fairness mean we must not exceed • Recall TCP average throughput simplistic model • TCP throughput is inversely proportional to • RTT and square root of packet loss probability p

  8. Loss-Delay Based Adjustment Algorithm • Calculating RTT • No ACK in UDP • Use feedback report • Where t= arrival time, = time elapsed since last report, and = last received sender report

  9. Performance of LDA • LDA and TCP

  10. Performance of LDA • LDA scalability

  11. In Theory, It Works • Not In Practice • Additional network overhead (RTP) • Additional application level complexity • Rogue UDP process could starve TCP-Friendly protocols • Performance Driven • UDP is intended to be light weight and fast • TCP-Friendly protocols would have to yield to UDP • Developers are lazy, they want the fastest connection with minimal amount of work

  12. Summary • TCP-Friendly Protocols • UDP based protocols with congestion control • Able to sense the network and adjust send rate accordingly • Promote fair bandwidth sharing • Prevents Network Collapse • Work together with TCP to balance bandwidth • Fill The Gap • TCP-Friendly protocols can fill the gap between TCP and UDP

  13. References • TCP-Friendly, Advanced Networking: Pittsburgh Supercomputing Center, http://www.psc.edu/networking/projects/tcpfriendly/ • D. Sisalem, H. Schulzrinne, “The Loss-Delay Adjustment Algorithm: A TCP-friendly Adaptation Scheme”, Network and Operating System Support for Digital Audio and Video (NOSSDAV ‘98), Cambridge, UK, July 8-10, 1998. • J. Mahdavi, S. Floyd, TCP-Friendly Unicast Rate-Based Flow Control http://www.psc.edu/networking/papers/tcp_friendly.html • Lorenzo Vicisano, Luigi Rizzo (Pisa) and Jon Crowcroft, TCP-like Congestion Control for Layered Multicast Data Transfer (INFOCOM ‘98).

More Related