CS 34701: Large-Scale Networked Systems

1. CS 34701: Large-Scale Networked Systems Professor: Ian Foster TA: Adriana Iamnitchi http://dsl.cs.uchicago.edu/Courses/cs347-2002/

2. CS 34701 Course Goals • Primary • Gain deep understanding of fundamental issues that effect design of large-scale networked systems • Map primary contemporary research themes • Gain experience in network research • Secondary • By studying a set of outstanding papers, build knowledge of how to present research • Learn how to read papers & evaluate ideas

3. How the Class Works • Research papers • Prior to each class, we all read and evaluate two research papers • During each class, we discuss those papers • Project • One-page project description by 2nd week • Five-page project summary by 5th week • 10-20 final paper by 9th week • Project presentations: 9th and 10th weeks.

4. Paper Review & Discussion • Everyone reads two papers per class and submits an evaluation (see below) • We discuss (not present) papers in class • A team of 2-3 leads each discussion • The leading team submits discussion plan before class, submits “master critique” and summarizes discussion at the beginning of following class • Look over schedule between now & Friday, when we will allocate discussants

5. Evaluations • You must submit evaluations of papers • Email them by 6pm the day before • Answer a set of standard questions • State the main contribution of the paper • Critique the main contribution • What are the three strongest and/or most interesting ideas in the paper? • Three most striking weaknesses in the paper? • Three questions to ask the authors? • Detail an interesting extension to the work not mentioned in the future work section. • Optional comments on the paper that you’d like to see discussed in class.

6. What I’ll Assume You Know • Basic Internet architecture • IP, TCP, DNS, HTTP • Basic principles of distributed computing • Asynchrony (cannot distinguish between communication failures and latency) • Partial global state knowledge (cannot know everything correctly) • Failures happen. In very large systems, even rare failures happen often • If there are things that don’t make sense, ask!

7. Large-Scale Networked Systems • Internet-connected networks with a large number of components, spanning multiple DNS domains (usually WAN) • Designed to solve specific problems: • Content distribution • Cycle sharing • File sharing • Sensor data fusion • Distributed data analysis • …

8. Example: Gnutella • Peer-to-peer file sharing system • File sharing: goal is to enable publication and access to files • P2P: no central servers; all clients also act as servers and are equivalent (more or less) • Issues • Scaling to very large numbers of nodes • Properties: bootstrapping, reliability, cost, anonymity, security, freeloading, …

9. Gnutella Protocol Overview • P2P file sharing application on top of an overlay network: • Nodes maintain open TCP connections. • Messages are broadcasted (flooded) or back-propagated. • Protocol:

10. A Gnutella search mechanism • Steps: • Node 2 initiates search for file A 7 1 4 2 6 3 5

11. A A A Gnutella search mechanism • Steps: • Node 2 initiates search for file A • Sends message to all neighbors 7 1 4 2 6 3 5

12. A A A A Gnutella search mechanism • Steps: • Node 2 initiates search for file A • Sends message to all neighbors • Neighbors forward message 7 1 4 2 6 3 5

13. A A A A:5 A:7 Gnutella search mechanism • Steps: • Node 2 initiates search for A • Sends message to all neighbors • Neighbors forward message • Nodes that have file A initiate a reply message 7 1 4 2 6 3 5

14. A A A:5 A:7 Gnutella search mechanism • Steps: • Node 2 initiates search for A • Sends message to all neighbors • Neighbors forward message • Nodes that have file A initiate a reply message • Query reply message is back-propagated 7 1 4 2 6 3 5

15. A:5 A:7 Gnutella search mechanism • Steps: • Node 2 initiates search for A • Sends message to all neighbors • Neighbors forward message • Nodes that have file A initiate a reply message • Query reply message is back-propagated • Node 2 gets replies 7 1 4 2 6 3 5

16. Gnutella search mechanism • Steps: • Node 2 initiates search for A • Sends message to all neighbors • Neighbors forward message • Nodes that have file A initiate a reply message • Query reply message is back-propagated • Node 2 gets replies • File download download A 7 1 4 2 6 3 5

17. Tools for network exploration • Eavesdropper- modified node inserted into the network to log traffic. • Crawler- connects to all active nodes and uses the membership protocol to discover graph topology. • Parallelcrawling. • Graph analysistools • high-volume offline computations.

18. Network growth • High user interest: • Users tolerate high latency, low quality results. • Better resources: • DSL and cable modem nodes grew from 24% to 41% over 6 months. • Open architecture / open-source environment: • Competing implementations, • Lower overhead network traffic, improved resource utilization, better structure, • Recently, two-level structure.

19. Growth invariants Graph connectivity: 3.4 links per node on average. Path length distribution: node-to-node distance maintains similar distributions. • Avg. node-to-node distance grew 25% while the network grew 50 times over 6 months. • Random graph theory predicts about 75% increase.

20. Is Gnutella a power-law network? Power-law networks: the number of nodes N with exactly L links is proportional to L-kN ~ L-k Examples: • The Internet, • In/out links to/from HTML pages, • Citations network, • US power grid, • Social networks. November 2000 Implication: High tolerance to random node failure but low reliability when facing an ‘intelligent’ adversary

21. Is Gnutella a power-law network? • Later, larger networks display a bimodal distribution. • Implications: • High tolerance to random node failures preserved • Increased reliability when facing an attack. May 2001

22. Trafficanalysis •  6-8 kbps per link over any connection. • Traffic structure changed over time.

23. Total generated traffic 1Gbps (or 330TB/month)! • Note that this estimate excludes actual file transfers • Q: Does it matter? • Compare to 15,000TB/month estimated in US Internet backbone (Dec. 2000). Reasoning: • QUERYandPINGmessages are flooded. They form more than 90% of generated traffic • predominant TTL=7 • >95% of nodes are less than 7 hops away • measured traffic at each link about 6 to 8kbs • network with 50k nodes and 170k links

24. Topology mismatch The overlay network topology doesn’t match the underlying Internet infrastructure topology! • 40% of all nodes are in the 10 largest Autonomous Systems (AS). • Only 2-4% of all TCP connections link nodes within the same AS. • Largely ‘random wiring’. • Entropy experiment gives similar results.

25. Course Topics • Internet Architecture and Design Principles • Flat Pricing vs. Prioritized Traffic • Internet Measurements • Availability in Wide-Area • Patterns in Real Networks • Modeling the Internet Topology • Internet Services: DNS • Web Caching, Content Distribution Networks • Overlay Networks • Peer-to-Peer systems • Computational Grids • Security Issues • Sensor Nets • Wireless Networks • XML SOAP and Web Services

26. Course Topics • Internet Design Principles • How do I deliver Internet services: end-to-end vs. within the network? • Flat Pricing vs. Prioritized Traffic • How do I determine which traffic to pass over the Internet? • Internet Measurements • What does the Internet really look like?

27. Course Topics • Availability in Wide-Area • How reliable is the Internet? • Patterns in Real Networks • What does Internet traffic look like? • Modeling the Internet Topology • How can I construct realistic models of Internet structure?

28. Course Topics • Internet Services: DNS • How well does DNS work? • Web Caching, Content Distribution Networks • How do we optimize Web content mgmt? • Overlay Networks • Improving routing performance

29. Course Topics • Peer-to-Peer systems • Gnutella, etc., etc. • Computational Grids • Globus, etc. • Security Issues • Authorization, etc.

30. Disaster Response Circulatory Net Course Topics • Sensor Nets • How do I structure & program networks of lightweight devices? • Wireless Networks • How do I route in ad hoc networks? • XML SOAP and Web Services • What are Web services anyway?

31. Projects • Literature surveys, real implementations, analytical evaluations • Can be performed individually or in a team of two • Your project ideas appreciated (to be discussed before proposal due date) • Primary goal is to do something interesting and to do it well

32. Example Project • Gnutella network analysis • Develop a “crawler” that traverses network, collects membership & connectivity info • Analyze structure • Characterize structure • See, e.g.: • Mapping the Gnutella Network: Properties of Large-Scale Peer-to-Peer Systems and Implications for System Design, M. Ripeanu, I. Foster, A. Iamnitchi, in IEEE Internet Computing Journal, vol. 6(1), 2002

33. Project Ideas • http://dsl.cs.uchicago.edu/Courses/cs347-2002/cs347_projects.htm • Gnutella network measurements • Topology discovery for 500K nodes • Structural analysis with 500K nodes • Study impact of overlay networks • Etc.

34. Project Ideas • Overlay networks: build unstructured or semistructured self-organizing overlays optimizing different cost functions: • Topology-aware: map onto physical infrastructure • Usage-aware: map onto usage patterns • Analysis of Sloan Digital Sky Survey logs to explore access patterns • What files are accessed how often • What community usage patterns emerge? • How can we exploit these in content distribution networks?

35. Project Ideas • Compare qualitatively and analytically current file-location solutions (CAN, Chord, Gnutella, Napster, etc.) in the context of scientific file-sharing collaborations. • Evaluate sharing patterns based on real usage traces in a scientific collaboration • Use these patterns to evaluate benefits/drawbacks and propose better alternatives • Expand existing simulator to evaluate request forwarding techniques for resource location in grid environments

36. For More Information • Contact me • Ian Foster, foster@cs.uchicago.edu • Email or set up a meeting • Contact Anda, our TA • Adriana Iamnitchi, anda@cs.uchicago.edu • Monitor the class web page • http://dsl.cs.uchicago.edu/Courses/cs347-2002/

37. Next 2 Classes • Friday: • Discuss: • J. Saltzer, D. Reed, and D. Clark, End-to-end Arguments in System Design. ACM Transactions on Computer Systems, Vol. 2, No. 4, pp. 195-206, 1984. • D. Clark and M. Blumenthal, Rethinking the design of the Internet: The end to end arguments vs. the brave new world, Workshop on Policy Implications of End-to-End. December 1, 2001. • Leading group: Ian + 2 volunteers (who?) • Wednesday: • Leading Group: Anda + 1-2 volunteers (who?)