CIS : Federated Distributed Systems Adriana Iamnitchi (Anda)

2 CIS6930.5: Federated Distributed Systems (Fall 2005) Contact Info Office: ENB 334 Office hours: Wednesdays, 10:45 – 1:00 and by appointment Course page:

3 CIS6930.5: Federated Distributed Systems (Fall 2005) Examples of Distributed Systems ATT webGnutella network The Internet A Sensor Network

4 CIS6930.5: Federated Distributed Systems (Fall 2005) Definition (a version) l A distributed system is a collection of autonomous, programmable, failure-prone entities that are able to communicate through a communication medium that is unreliable. –Entity=a process on a device (PC, PDA, mote) –Communication Medium=Wired or wireless network l “Federated” – spanning multiple institutional or network (DNS) domains

5 CIS6930.5: Federated Distributed Systems (Fall 2005) Outline l Case study: Seti, Napster, Gnutella l Administravia

6 CIS6930.5: Federated Distributed Systems (Fall 2005)

7 Operations data recorder screensavers WU storage splitters DLT tapes data server science DBuser DB result queue acct. queue garbage collector tape archive, delete tape backup master DB redundancy checking RFI elimination repeat detection web site CGI program web page generator

8 CIS6930.5: Federated Distributed Systems (Fall 2005) How does it work? l Fixed-rate data processing task l Low bandwidth/computation ratio l Independent parallelism l Error tolerance Master-worker architecture

9 CIS6930.5: Federated Distributed Systems (Fall 2005) History and Statistics l Conceived 1995, launched April 1999 l “scientific experiment that uses Internet-connected computers in the Search for Extraterrestrial Intelligence (SETI). You can participate by running a free program that downloads and analyzes radio telescope data. “ l No ET signals yet, but other results TotalLast 24 Hours (as of Wed Feb 23 07:04:51) Users5,361,3134,391 Results received1,779 millions5 million Total CPU time2.2 million years years Average CPU time/work unit 10 hr 58 min 14.0 sec6 hr 19 min 30.1 sec

10 CIS6930.5: Federated Distributed Systems (Fall 2005) Public-resource computing l Utilizes idle computing cycles over Internet l Other systems: –Original: GIMPS, distributed.net –Commercial: United Devices, Entropia, Porivo, Popular Power –Academic, open-source >Cosm,

11 CIS6930.5: Federated Distributed Systems (Fall 2005) None of the popularity of SETI! l ET l How to get and retain users (from David Anderson, the leader of the project) –Graphics are important (but monitors do burn in) –Teams: users recruit other users –Keep users informed l Science news l System management news l Periodic project s l Reward users: –PDF certificates –Milestone pages and s –Leader boards (overall, country, …)

12 CIS6930.5: Federated Distributed Systems (Fall 2005) Millions and millions of computers! (Problems) l Server scalability l Dealing with excess CPU time l Cheating l Bad behavior: –Team recruitment by spam –Sale of accounts on eBay l Malfunctions l Network bandwidth costs money

13 CIS6930.5: Federated Distributed Systems (Fall 2005) Summary l Master-worker design –Centralized solution >Master=central point of control >Single point of failure >Performance bottleneck l Incentives for participation –Mean sometimes incentives for cheating l Massive (“embarrassing”) parallelism l Low bandwidth/computation ratio Users do donate real resources: $1.5M / year consumed power l More information:

14 CIS6930.5: Federated Distributed Systems (Fall 2005) Outline l Case study: Seti, Napster, Gnutella l Administravia

15 CIS6930.5: Federated Distributed Systems (Fall 2005) Where is file A? The File Location Problem (Napster and Gnutella)

16 CIS6930.5: Federated Distributed Systems (Fall 2005) Napster: How It Works napster.com Client-server: Use central server to locate files Download files directly from peers

17 CIS6930.5: Federated Distributed Systems (Fall 2005) Napster users File list is uploaded 1. napster.com

18 CIS6930.5: Federated Distributed Systems (Fall 2005) Napster napster.com user Request and results User requests search at server. 2.

19 CIS6930.5: Federated Distributed Systems (Fall 2005) Napster napster.com user pings User pings hosts that apparently have data. Looks for best transfer rate. 3.

20 CIS6930.5: Federated Distributed Systems (Fall 2005) Napster napster.com user Retrieves file User retrieves file 4.

21 CIS6930.5: Federated Distributed Systems (Fall 2005) Napster: History l Program for sharing files over the Internet l History: –5/99: Shawn Fanning (freshman, Northeasten U.) founds Napster Online music service –12/99: first lawsuit –3/00: 25% UWisc traffic Napster –2000: est. 60M users –2/01: US Circuit Court of Appeals: Napster knew users violating copyright laws –7/01: # simultaneous online users: Napster 160K, Gnutella: 40K, Morpheus: 300K

22 CIS6930.5: Federated Distributed Systems (Fall 2005) Napster: Summary l Centralized server: –Client-server architecture –Single logical point of failure –Potential for congestion (bottleneck) –Napster “in control” (freedom is an illusion) l No security: –Passwords in plain text –No authentication –No anonymity

23 CIS6930.5: Federated Distributed Systems (Fall 2005) Outline l Public-resource computing –Case study: l Peer-to-peer systems –Case study 1: Napster –Case study 2: Gnutella l Discuss: –Characteristics –Impact –Architecture –Killer application

24 CIS6930.5: Federated Distributed Systems (Fall 2005) napster.com Gnutella: Search for Files with No Central Server

25 CIS6930.5: Federated Distributed Systems (Fall 2005) Where is file A? Ideas?

26 CIS6930.5: Federated Distributed Systems (Fall 2005) I have file A. Gnutella: Search Where is file A? Query Reply Flooding

27 CIS6930.5: Federated Distributed Systems (Fall 2005) Gnutella: History and Statistics l Gnutella history: –3/14/00: release by AOL, almost immediately withdrawn –too late: 1,859,340 users on Gnutella on August 25, 2am –many iterations to fix poor initial design l High impact: –Versions implemented –Different designs –Lots of research papers/ideas ( 06/24/’05) 251,137MP2P 294,255DirectConnect 1,146,880Overnet 1,516,762Gnutella 2,521,887FastTrack 4,123,688eDonkey2K NetworkUsers

28 CIS6930.5: Federated Distributed Systems (Fall 2005) What would you ask about Gnutella? l…l…l…l…

29 CIS6930.5: Federated Distributed Systems (Fall 2005) Gnutella: Heterogeneity All Peers Equal? (1) 56kbps Modem 10Mbps LAN 1.5Mbps DSL 56kbps Modem 1.5Mbps DSL

30 CIS6930.5: Federated Distributed Systems (Fall 2005) Gnutella: Free Riding All Peers Equal? (2)  More than 25% of Gnutella clients share no files; 75% share 100 files or less  Conclusion: Gnutella has a high percentage of free riders l If only a few individuals contribute to the public good, these few peers effectively act as centralized servers. Adar and Huberman (Aug ’00)

31 CIS6930.5: Federated Distributed Systems (Fall 2005) Flooding in Gnutella: Loop Prevention Seen request already

32 CIS6930.5: Federated Distributed Systems (Fall 2005) Gnutella Topology Mismatch

33 CIS6930.5: Federated Distributed Systems (Fall 2005) Gnutella Summary l Search by flooding l Self-configuring l Phenomena: –Not all peers equal –Free riding l Problems: –Topology mismatch –Duplicates due to flooding l Good source for technical info/open questions: –

34 CIS6930.5: Federated Distributed Systems (Fall 2005) Problems in Distributed Systems l … l Communication –Routing [IP,BGP] –Multicast [IP multicast, SRM, RMTP] l Post and retrieve [Usenet] l Search [Gnutella, Kazaa, etc., Google] l Storage [Databases] l Coordination l …

35 CIS6930.5: Federated Distributed Systems (Fall 2005) Challenges l … l Failures l Scale l Asynchrony l Security l Deployment l Adoption l …

36 CIS6930.5: Federated Distributed Systems (Fall 2005) Challenges (2) l … l Learn from usage –Example 1: The Internet –Example 2: Napster l Conflicting requirements: –Light but adaptable? –Light but data-consistent? (think transactions) –… (other examples?) l … (other examples?)

37 CIS6930.5: Federated Distributed Systems (Fall 2005) Course Organization/Syllabus/etc.

38 CIS6930.5: Federated Distributed Systems (Fall 2005) Administravia: Grading l Reviewing:30% l Discussion leading: 15% l Project: 55% –Aim high! –Have fun!

39 CIS6930.5: Federated Distributed Systems (Fall 2005) Administravia: Paper Reviewing (1) l Goals: –Think of what you read –Get used to writing paper reviews l Reviews due by midnight before class Follow the form when relevant. l State the main contribution of the paper l Critique the main contribution. –Rate the significance of the paper on a scale of 5 (breakthrough), 4 (significant contribution), 3 (modest contribution), 2 (incremental contribution), 1 (no contribution or negative contribution). Explain your rating in a sentence or two.

40 CIS6930.5: Federated Distributed Systems (Fall 2005) Administravia: Paper Reviewing (2) Rate how convincing the methodology is. l Do the claims and conclusions follow from the experiments? l Are the assumptions realistic? l Are the experiments well designed? l Are there different experiments that would be more convincing? l Are there other alternatives the authors should have considered? l (And, of course, is the paper free of methodological errors?)

41 CIS6930.5: Federated Distributed Systems (Fall 2005) Administravia: Paper Reviewing (3) l What is the most important limitation of the approach? l What are the three strongest and/or most interesting ideas in the paper? l What are the three most striking weaknesses in the paper? l Name three questions that you would like to ask the authors. l Detail an interesting extension to the work not mentioned in the future work section. l Optional comments on the paper that you’d like to see discussed in class.

42 CIS6930.5: Federated Distributed Systems (Fall 2005) Paper Reviewing (final) l Be professional in your writing l Have an eye on the writing style: –Clarity –Beware of traps: learn to use them in writing and detect them in reading –Detect (and stay away from) trivial claims. E.g., 1 st sentence in the Introduction: “The tremendous/unprecedented/phenomenal growth/scale/ubiquity of the Internet…”

43 CIS6930.5: Federated Distributed Systems (Fall 2005) Administravia: Discussion leading l Come prepared! –Prepare discussion outline –Prepare questions: >“What if”s >Unclear things >… –Similar ideas in different contexts –Initiate short brainstorming sessions l Leaders do NOT need to submit paper reviews l Main goals: –Keep discussion flowing –Keep discussion relevant –Engage everybody (I’ll have an eye on this, too)

44 CIS6930.5: Federated Distributed Systems (Fall 2005) Administravia: Projects l Combine with your research if relevant to the class l Get approval from all instructors if you overlap final projects: –Don’t sell the same piece of work twice –You can get more than twice as many results with less than twice as much work l Aim high! –Put one extra month and get a publication out of it –It is doable l Try ideas that you postponed out of fear: it’s just a class, not your PhD.

45 CIS6930.5: Federated Distributed Systems (Fall 2005) Administravia: Project deadlines (tentative) l Sept. 15: 1-page project proposal l Oct. 11: 3-page literature survey –Know relevant work in your problem area –If implementation project, list tools, similar projects l Nov. 11: 5-page Midterm project due –Have a clear image of what’s possible/doable –Report preliminary results l Last class(es):In-class project presentation –Demo, if appropriate l Dec. 16: –10-page write-up

46 CIS6930.5: Federated Distributed Systems (Fall 2005) Next Class (Wed, August 31) l Read the 4 chapters from the Grid book l Send brief summaries (lists of ideas/problems discussed, etc) –Do not follow the reviewing form –Be brief and efficient! –Be BRIEF and EFFICIENT! l In-class discussion + some project ideas l Need discussion leader to team up with me for the class next week: –The structure of networks (pick 2): 1.Small-world file sharing communities, Iamnitchi, Ripeanu, Foster. Infocom On Power-Law Relationships of the Internet Topology, Faloutsos, Faloutsos, and Faloutsos, SIGCOMM Mapping the Gnutella network, M. Ripeanu et al, IEEE Computing Journal 2002.

47 CIS6930.5: Federated Distributed Systems (Fall 2005) Questions?