1. P4P: Proactive Provider Assistance for P2P Haiyong Xie (Yale) haiyong.xie@yale.edu *This is a joint work with Arvind Krishnamurthy (UWashington) and Richard Yang (Yale).

2. 2007-5-25 1st NYC P2P Workshop 2 Roadmap  Motivation  P4P framework  Design rationale  System architecture  Computing peering suggestions  Evaluations  Conclusion and future work

3. 2007-5-25 1st NYC P2P Workshop 3 P2P : The Significant Bandwidth Consumer Up to 60-70% of Internet traffic is contributed by P2P applications [cachelogic] Problems  Scattered traffic  Increased network utilization  Degraded performance of other applications  Increased network operational costs http://www.cachelogic.com

4. 2007-5-25 1st NYC P2P Workshop 4 Bandwidth Battle between ISPs and P2P The battle results in a lose-lose situation  ISPs: increased financial and operational costs, increased network utilization, degraded performance  P2P: increased complexity of P2P applications, reduced interoperability, and impeded development of P2P applications ISPs try to “manage” P2P traffic  Upgrade network infrastructure  Deploy P2P caching devices  Rate limit P2P traffic P2P tries to evade from being captured  Use random ports  Encrypt traffic

5. 2007-5-25 1st NYC P2P Workshop 5 Objective: Where are the problems?  ISPs do not disclose their network information for privacy concerns  P2P does not have sufficient information to determine network-aware peering relationships ISPs can expose information to “guide” the peering relationships in P2P systems to  Improve the throughput of P2P users  Lower traffic costs for ISPs, balance traffic across the network Design a framework so that ISPs and P2P can work together to achieve better results

6. 2007-5-25 1st NYC P2P Workshop 6 P4P Framework – Design Rationale Scalability  Support a large number of P2P users and networks in dynamic settings Privacy preservation Try to improve performance for both ISPs and P2P Extensibility  Application-specific requirements  Tracker-based vs. trackerless P2P systems  Gossip among peers Incremental deploymentability

7. 2007-5-25 1st NYC P2P Workshop 7 ISP A Design For Tracker-based P2P 1 4 3 2 pTrackeriTracker peer Use BitTorrent in a single ISP as an example  pTracker keeps P2P system states  iTracker makes suggestions for peering relationships Information flow:  1. peer queries pTracker  2. pTracker asks iTracker for guidance  3. iTracker returns high- level peering suggestions  4. pTracker selects and returns a set of active peers, according to the suggestions iTracker can be run by third parties trusted by ISPs.

8. 2007-5-25 1st NYC P2P Workshop 8 Service Interfaces and States Services provided by iTracker  Map an IP address to an opaque, privacy-preserving PID PID = getpid(ip )  Compute peering suggestions for a given PID-based P2P state [w ij ] = getpeering(PID-based-state) w ij : probability with which peers of PID i establish peering relationship with peers of PID j pTracker keeps states  PID-peer state (updated by calling getpid() interface call)  P2P state (updated by collecting peer information) PIDcounterupcapdowncap …… inini uiui didi PIDPeer list …… ipipi

9. 2007-5-25 1st NYC P2P Workshop 9 How to Use iTracker Services When a new peer joins the P2P network and queries the pTracker  pTracker gets the PID for this peer by calling getpid()  pTracker updates its internal P2P state  pTracker gets the PID-based peering suggestion [w ij ] by calling getpeering()  pTracker selects a set of active peers according to [w ij ] and returns it [w ij ] can be used to represent the peering relationships among peers, and can be used to analyze performance  Original BitTorrent protocol selects peers randomly: w ij = n j / ∑n k  BitTorrent through caching (each PID has a caching peer only, and the remaining peers in the same PID peers with the cache): w ij = 0 for non-caching peers and i≠j

10. 2007-5-25 1st NYC P2P Workshop 10 Pros and Cons Evaluate the design  Pros iTracker is stateless Need no modification to P2P clients Preserve privacy  Cons Cannot handle trackerless P2P systems Cannot handle gossip

11. 2007-5-25 1st NYC P2P Workshop 11 ISP A The Complete Design 1 pTracker iTracker Peer a iTracker’s responsibilities  Keeps P2P system states (PID-based, light-weight)  makes suggestions for peering relationships Information flow:  1. peers register or update with iTracker  2. iTracker returns PID and PID-based peering suggestions  3. Peers exchange peer information (with associated PID information) through gossips  4. Peers update peering relationships according to the received peering suggestions Peer b 3 1 22

12. 2007-5-25 1st NYC P2P Workshop 12 How iTracker Works – Computing Peering Suggestions ISP’s model  ISP’s network is a graph G=(V,E)  Link utilization b e due to background traffic on edge e  I e (i,j)=1 iff edge e is on the route from node i to j, determined by ISP’s routing scheme P2P’s model  There are K P2P systems  Uploading/downloading capacity for all peers with PID i: u i k, d i k  Traffic uploaded from PID-i peers to PID-j peers: t ij k Peering suggestion  Allow a certain number of random connections to ensure robustness

13. 2007-5-25 1st NYC P2P Workshop 13 How iTracker Works – Computing Peering Suggestions (cont ’ d) Formulate as a joint optimization problem  ISP’s objective: minimize maximum link utilization  P2P’s objective: maximize throughput  Joint optimization: min max link utilization for ISP when P2P throughput is maximized

14. 2007-5-25 1st NYC P2P Workshop 14 How iTracker Works – Computing Peering Suggestions (cont ’ d) Naïve approach takes multiple steps  Get optimal throughput T opt k for each P2P system k by solving its corresponding optimization problem individually  Solve the ISP optimization problem with constraints of each P2P system’s throughput being maximized One-step approach through duality transformation  Apply dual transformation to P2P optimization problem  Obtain a new optimization problem by merging ISP and dual P2P problems

15. 2007-5-25 1st NYC P2P Workshop 15 Roadmap Motivation P4P framework Design rationale System architecture Computing peering suggestions Evaluations  Conclusion and future work

16. 2007-5-25 1st NYC P2P Workshop 16 Evaluation – Methodology Simulations  Discrete-event simulation a module for modeling BitTorrent protocol a module for modeling underlying network topology and data transfer dynamics using TCP rate equation  Network topology: PoP-level AT&T and Abilene topologies  Network routing: OSPF routing PlanetLab experiments  53 Internet2 nodes on PlanetLab  iTracker for Abilene network  Use OSPF routing to re-construct traffic load on Abilene links

17. 2007-5-25 1st NYC P2P Workshop 17 Evaluation – Abilene Simulation Compared to P4P, native P2P can result in  2x download completion time  2x higher link utilization Native P2P can result in some peers experiencing very long download completion time Native P2P can result in much larger variance in link utilization

18. 2007-5-25 1st NYC P2P Workshop 18 Evaluation – AT&T Simulation Compared to P4P, native P2P can result in  1.6x download completion time  3x higher link utilization Some peers can experience very long download completion time with native P2P Link utilization variance can be larger for native P2P

19. 2007-5-25 1st NYC P2P Workshop 19 Evaluation – Liveswarms on Planetlab Liveswarms* is a P2P-based video streaming application, which adapts BitTorrent protocol to video streaming context Run liveswarms on 53 PlanetLab nodes for 900 seconds P4P and native liveswarms achieve roughly the same amount of throughput P4P reduces link load  Average link load saving is 34MB  Maximum average link load saving is 60% Native liveswarms:1Mbps P4P liveswarms: 432Kbps *Michael Piatek, Colin Dixon, Arvind Krishnamurthy, Tom Anderson. LiveSwarms: Adapting BitTorrent for end host multicast. Technical report: UW-CSE-06-11-01

20. 2007-5-25 1st NYC P2P Workshop 20 Conclusion and Future Work Our design achieves the objective  Scalability: iTracker is light-weight, maintains necessary states only  Privacy preservation  Extensibility  Robustness  Performance improvement for both ISPs and P2P Incremental deploymentability Implementation Incentives

21. 2007-5-25 1st NYC P2P Workshop 21 Questions?

22. 2007-5-25 1st NYC P2P Workshop 22 Backup Slides

23. 2007-5-25 1st NYC P2P Workshop 23 Computation cost is low Among 34K+ swarms, <1% have more than 100 leechers, and about1% swarms contribute to 50% of traffic demand Solution time of the optimization problem is linear to number of swarms (slope ≈ 0.025)