Measurement-Based Optimization Techniques for Bandwidth-Demanding Peer-to-Peer Systems
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Transcript of Measurement-Based Optimization Techniques for Bandwidth-Demanding Peer-to-Peer Systems
Measurement-Based Optimization Techniques for
Bandwidth-Demanding Peer-to-Peer Systems
T. S. Eugene Ng, Yang-hua Chu, Sanjay G. Rao, Kunwadee Sripanidkulchai and Hui Zhang
Appeared in INFOCOM 2003
Presented By Felix Lam
Introduction
Bandwidth-demanding P2P applications like file sharing or overlay multicast systems have performance depending on the selection of peers.
Goal File Sharing - Find peer(s) with as high bandwidth as p
ossible Overlay multicast systems - Find peer that provides suf
ficient bandwidth for streaming Shorter Convergence time
Introduction
Three light-weight measurement-based techniques for peer selection RTT Probing
Using a single 36 Byte ICMP ping message; the peer with smallest RTT is selected.
10 KB TCP probing1
Download 10 KB of data from each peer through a TCP connection; the peer with the shortest download time is selected.
1. Suggested in J. Jannotti, D. Gifford, K. L. Johnson, M. F. Kaashoek, and J. W. O, “Overcast:Reliable multicasting with anoverlay network,” Proc. Fourth Symposium on Operating System Design and Implementation (OSDI), Oct. 2000
Introduction
Cont’ Bottleneck Bandwidth Probing (BNBW)
Use nettimer2 to measure BNBW to each candidate peer; the peer with the largest BNBW is selected
2. K. Lai and M. Baker, “Nettimer: A tool for measuring bottleneck link bandwidth,” Proc. 3rd USENIX Symposium on InternetTechnologies and Systems, Mar. 2001.
Introduction
Interesting Questions: How well can each individual technique identify
a peer with high TCP available bandwidth? What is the fundamental limitations of a
technique? Can adaptive applications benefit from using the
basic techniques? Can multiple basic techniques be exploited
simultaneously?
Trace-based Analysis
Peer Traces Collection Peers are chosen “randomly” from the Open Napster s
ervers Data collected from each peer
Total time to download 500KB of data from the peer via TCPThe time taken to download the initial 10KB of dataRTT of ten 36-byte pings to the peerThe bottleneck link bandwidth found using nettimer between C
MU and the chosen peers
……
Trace-based Analysis
Trace-based Analysis
How is the analysis done? In each experiment, 100 peers are chosen randomly Then the 3 techniques are applied independently to select a
peer An optimality Ratio (O.R.) is computed as the TCP throughput
of the selected peer divided by the TCP throughput of the best peer among the 100 peers.
1000 experiments are done, the average O.R. for each method is reported
How well does each technique perform?
40% - 50% O.R. 10KB Probe and BNBW
are only a bit better than RTT probing
Unusually high correlation between delay and bandwidth, because network access tech. affects delay
Limitations of Basic Techniques
Inherent Difficulty of Peer Selections
Rank of selected peer O.R.
1 1
2 0.73
3 0.6
4 0.51
Significant performance drop by selecting a slightly lower ranked peer
Limitations of Basic Techniques
Peer Selection or Peer Elimination? To answer this, in each experiment, we choose the
worst and the best N peers respectively, and compare the accuracy versus N
Limitations of Basic Techniques Inability to Differentiate Good Peers
Progressively remove 5% of the worst peers at a time O.R. does not improve even when there are only good
peers
Limitations of Basic Techniques Using Basic Techniques in Adaptive Applications
Adaptively select peers based on past observation on TCP throughput (e.g. changing parents in overlay multicast streaming applications)
Remove 95 or 90 worst performing peers, and find out the best performing peers based on observation on the TCP throughputs of the remaining peers
>80 % given 5 trials
Limitations of Basic Techniques
Complementarity Analyses of Basic Techniques From the results, clearly the three can complement each other, in o
rder words, they seldom select “good” peers at the same time. If we follows the recommendation of the most successful technique
among the three, O.R. of 0.73 can be achieved
Limitations of Basic Techniques Complementarity Analyses of Basic Techniques (Cont’)
However, it consumes a lot of time to perform all 3 types of probing techniques on all 100 candidates
Can we first use RTT probing to eliminate 95 worst peers and perform the 10KB and BNBW probing on the remaining 5 peers?
• By doing so, we get O.R. of 0.68 < 0.73• A little trade-off between the selection performance and probing overhead
Application Case Studies Media File Sharing
Assume the entire media file is downloaded from the chosen peer no retrial
Joint Ranking Sum up the rank values of 2 or more techniques; choose the peer with lowest su
med rank
•Joint Ranking improve the O.R.•Adopting RTT filtering is a good choice to probing overhead•Still far from the theoretically possible O.R. of 0.82 (oracle)
Application Case Studies
Overlay Multicast Streaming Extend from the Narada3 overlay multicast protocol, and
test with a Internet testbed with 29 hosts
3. Y. Chu, S. G. Rao, S. Seshan, and H. Zhang, “Enabling conferencing applications on the Internet using an overlay multicast architecture,” Proc. ACM SIGCOMM, August 2001.
Application Case Studies
Overlay Multicast Streaming (Cont’) Can Joint Ranking further improve?
•No significant improvement brought by Joint-Ranking•Using slightly better peer selection technique cannot bring significant improvement to adaptive applications•The key is to make quick adaptation decisions based on useful hints like RTT.. etc.
Conclusion First study of light-weight measurement techniques on
peer-to-peer applications Key insights
Peer selection is inherently challenging problem With light-weight measurements, the performance of peer selection
can improve significantly The techniques work better in eliminating bad peers than selecting
good peers With adaptive peer selection (e.g. in overlay multicast), the
performance can be further enhanced by light-weight measurements
The techniques are highly complementary and can be combined to give better performance
Comments
Pro Very rich trace-based and internet-based
experiment results to illustrate the performance of light-weight probing techniques.
Very useful and interesting discovery about the high correlation between RTT and bandwidth
Con The discussions does not capture the high
dynamicity of network bandwidth