Download presentation
Presentation is loading. Please wait.
Published byAlayna Mabbitt Modified over 10 years ago
1
1 School of Computing Science Simon Fraser University CMPT 771/471: Internet Architecture & Protocols TCP-Friendly Transport Protocols
2
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
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
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
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
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 7
8
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
9 Performance of LDA LDA and TCP
10
10 Performance of LDA LDA scalability
11
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
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
13 References TCP-Friendly, Advanced Networking: Pittsburgh Supercomputing Center, http://www.psc.edu/networking/projects/tcpfriendly/ 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 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).
Similar presentations
© 2024 SlidePlayer.com Inc.
All rights reserved.