1. Peer-to-Peer EE 122: Intro to Communication Networks Fall 2010 (MW 4-5:30 in 101 Barker) Scott Shenker TAs: Sameer Agarwal, Sara Alspaugh, Igor Ganichev, Prayag Narula http://inst.eecs.berkeley.edu/~ee122/ Materials with thanks to Jennifer Rexford, Ion Stoica, Vern Paxson and other colleagues at Princeton and UC Berkeley

2. Today’s Lecture The Opening Act (~30 minutes) –Scott talking about Peer-to-Peer Systems The Main Event (rest of the time, and beyond) –Igor Ganichev talking about Networking Libraries 2

3. Ground Rules No slides (for me) –No laptops for you I won’t test you on anything from this lecture –This is for context I will give you homework on a P2P system –But based on material in the book –Won’t be hard –Some material covered in section 3

4. Peer-to-Peer Design paradigm: No central contol –Large number of identical nodes –Highly resilient and scalable –Just what you need to run a large datacenter Economic model: leverage user nodes –No need for huge investment –Broad geographic distribution –Self-scaling Will discuss both, but start with economic model…. –A continuing struggle for control 4

5. In the beginning….. AT&T created the telephone network First large-scale person-to-person communication infrastructure –The patent dispute of the telephone makes our patent litigation battles seem like child’s play The Telephone network dominated for two generations…. 5

6. The Telephone Model Functionality controlled by network operator –They sink the money into the infrastructure –They get to decide what that infrastructure does –But government regulated company (set ROI, etc.) End-user only has “dumb terminal” –Legally restricted in its use of that terminal –Until the court’s finally gave some freedom to users Regulated monopoly led to glacial innovation in functionality but extreme reliability and polish –Why spend money on features no one knows they want? –Spend money improving what people notice (failures) 6

7. Then came the Internet… End points had complete freedom, and substantial computing power –Infrastructure just carried bits Completely different economic model –Small guys can innovate –Big guys run dumb infrastructure (like utilities) Result: –Rapid innovation in applications (e.g., email, web) –Diversity of content (on web) –Low barrier to entry And finally, even the big boys noticed…. 7

8. The Empire Strikes Back Zipf’s law restores order to the universe –Popularity ~ 1/rank –Lots of weight at top (people like the same things) –Lots of weight in tail (but lots of idiosyncratic tastes) A Tale of Two Markets –Lots of action in the tail (anyone can play) –But only a few really big guys (hard to enter this market) High barrier to entry: CDNs –Bandwidth –Servers –Management 8

9. Revenge of the Nerds Peer-to-Peer restores the balance –Takes “contributed” nodes from participants –Together they provide enough aggregate bandwidth The key is in coordinated these peer nodes –First: Napster (Shawn Fanning) Academia followed (as it always does) My lecture on how academia has missed out on everything? –We are really good at solving problems –We are really terrible at figuring out what people want….. 9

10. Coordination Mechanisms Must be: –Scalable –Fault-tolerant –Can use commodity parts A good way to build systems in general! Now finished with P2P as economic model –Moving on to…….. 10

11. Peer-to-Peer as Design Paradigm Once you can coordinate many disparate peers –You can certainly coordinate many co-located peers –Now the dominant design style in datacenters –DHT-like data structures are everywhere This is what made Google work: (like Jobs at App) –Design as if failure is the typical case –Recover from failure only at the highest possible layer oIf routing fails use another server, don’t wait for routing to recover oThis is hard to accept for some people…. –Low cost components –Scale out, not up 11

12. P2P Systems Do Three Main Things Help user determine which content they want –Some form of search –P2P form of Google Then locate that content –Locate where that content is on the Internet –P2P form of DNS (map name to location) Then download that content –P2P form of Akamai 12

13. We need P2P forms of Search (keyword) Directory CDN What kinds of coordination mechanisms do we need for these tasks? 13

14. P2P Search Basic approach: –Since search can be complicated, just do it on each machine independently, and keep going for as long as you need Examples: –Broadcast –Broadcast among superpeers –Random walk (theory) Cannot match efficiency of Google 14

15. P2P Directory In most cases, a few centralized servers will do If you need to scale further, then use DHT –Put/Get interface DHT: simple version is consistent hashing –Everyone knows set of servers –Map key to server using the successor rule 15

16. P2P Download The first key here is self-scaling If every person who downloads something also has to upload it to someone else, the system works The second key here is asymmetric bandwidth –That’s where chunks come in –Downloading many chunks 16

17. Modern P2P Systems Use a Mixture Search to find name (wildcard search) –Flood among superpeers Directory lookup to find host given exact name –DHT-like structure Chunked download –Self-scaling –Asymmetric bandwidth 17