1. On the Effectiveness of Measurement Reuse for Performance-Based Detouring David Choffnes Fabian Bustamante Fabian Bustamante Northwestern University INFOCOM 2009

2. David Choffnes, CDN-based Detouring, INFOCOM 2009 Detouring FTP transfer between UCB and Dartmouth UC Berkeley Dartmouth 300 KB/s Intel Research 400 KB/s 2

3. David Choffnes, CDN-based Detouring, INFOCOM 2009 Detouring UC Berkeley Dartmouth 286 ms Intel Research 78 ms 0.8 ms 3

4. David Choffnes, CDN-based Detouring, INFOCOM 2009 Choosing Alternate Paths 4

5. David Choffnes, CDN-based Detouring, INFOCOM 2009 Locating Detour Paths Guess randomly –SOSR [Gummadi et al, NSDI 2005] –Improves reliability, but not necessarily performance Brute force –RON [Andersen et al, SOSP 2001] –All-to-all measurements (O(n 2 )) 100 nodes: ~100 Kbps at each node 100,000 nodes: ~100 Mbps at each node! –Fundamentally architecturally unsound –Wasteful for every system to try to measure Can we reuse someone else’s measurements? 5

6. David Choffnes, CDN-based Detouring, INFOCOM 2009 Reduce, Reuse, Recycle (3R) –Long-running services already measuring the network –Sustainable yield by reducing wasted Internet resources from distributed systems through strategic reuse and recycling of network information Long-running services as oracles –Low-cost, open sources of information about the network –Examples Content distribution networks P2P file sharing Sustainable Scalability 6

7. David Choffnes, CDN-based Detouring, INFOCOM 2009 CDNs as Potential Oracles Content distribution networks (CDNs) –Akamai, Limelight, Mirror Image –Serve popular sites like Yahoo, ABC.com, MySpace –Move load from content providers (e.g., Yahoo) to edge of network (CDN servers) –Provide interactive downloads for users by finding replicas along good network paths to users –Use extensive network measurements to inform replica server selection –Over 10,000 servers worldwide 7

8. David Choffnes, CDN-based Detouring, INFOCOM 2009 Road Map Introduction 3R: Reduce, Reuse, Recycle CDN-based detouring –Using CDNs as oracles –Locating high-performance paths –Building a system to exploit them Conclusion 8

9. David Choffnes, CDN-based Detouring, INFOCOM 2009 9 How CDNs Work Web client’s request redirected to “nearby” server –Client gets web site’s DNS CNAME entry with domain name in CDN network –Hierarchy of CDN’s DNS servers direct client to 2 nearby servers Internet Web client Hierarchy of CDN DNS servers Customer DNS servers (1) (2) (3) (4) (5) (6) LDNS Client requests translation for Yahoo Client gets CNAME entry with domain name in Akamai Client is given 2 web replica servers (fault tolerance) Web replica servers Multiple redirections to find nearby edge servers

10. David Choffnes, CDN-based Detouring, INFOCOM 2009 Using Redirections as Hints 10 Good path Replica server Host A Host B Also good? … in terms of latency [SIGCOMM ’06]

11. David Choffnes, CDN-based Detouring, INFOCOM 2009 From Redirections to Detouring Use CDN redirections as hints to identify candidate detour points Nodes experiencing similar redirection behavior are good detouring points for each other SideStep detouring service 11

12. SideStep Detouring Service 12 DNS lookups to determine redirection behavior Track ratio of time sent to each replica server Distribute these ratios so others with similar redirections can find each other N A : (r 1 =0.2, r 2 =0.8) N B : (r 1 =0.3, r 2 =0.7) Cosine Similarity: 0.91 DNS Lookups Ratio Manager Distributed Storage

13. SideStep Detouring Service 13 Compare redirection dynamics to determine candidate detour points Because hints are not facts, validate them via data races by sending data in parallel Abandon path with slower data rate Export API to enable applications to use detouring Client Stream Manager Race Manager DNS Lookups Detour Manager Ratio Manager Distributed Storage

14. David Choffnes, CDN-based Detouring, INFOCOM 2009 DraFTP Java-based client/server FTP suite Uses SideStep’s I/O stream interface Changed only 37 lines of code to port an existing FTP suite Publicly available under GPL license 14

15. David Choffnes, CDN-based Detouring, INFOCOM 2009 Evaluation Goals –Demonstrate redirections can identify detour points –Evaluate quality of detour points Experimental setup –Deployed on 170 machines worldwide (PlanetLab) –Initiated transfers between pairs of hosts picked at random –Evaluated 13,700 paths 15

16. David Choffnes, CDN-based Detouring, INFOCOM 2009 Overall Results Over half of evaluated paths improved performance Of those, 75% saw significant performance improvement (10% higher throughput) 11% more than doubled TCP throughput All of this is through without additional network monitoring 16

17. David Choffnes, CDN-based Detouring, INFOCOM 2009 Wide-area Evaluation 17 Direct path Race candidate detour path Switch to faster path Loses race

18. David Choffnes, CDN-based Detouring, INFOCOM 2009 Cumulative Results (Best cases) 18 If given only one shot, SideStep is almost always better Near-optimal performance after four tries

19. David Choffnes, CDN-based Detouring, INFOCOM 2009 Effects of different CDNs (Avg performance) 19 Different CDN names leads to different performance On average, random can pick very bad paths CDN-based paths are rarely worse on average

20. David Choffnes, CDN-based Detouring, INFOCOM 2009 Conclusion Advantages to SideStep –No path probing to locate detouring points –Requires only periodic DNS lookups –Scalable (O(n) overhead instead of O(n 2 )) –No new infrastructure required Open Issues –Fairness in detouring –Forwarding policies –Incentives for measurement sharing –… 20

21. David Choffnes, CDN-based Detouring, INFOCOM 2009 Questions? 21