Stealing From an Ongoing Flow: Protocols and Prototypes

1. Stealing From an Ongoing Flow: Protocols and Prototypes Ashu Sabharwal Rice University EPFL (2007-08) Joint work with Scott Novich & Debashish Dash

2. Microsoft Summit 2008 • Thanks to all the participants & Microsoft • Big thanks to Ranveer for putting all this together Rice University

3. 7 Blind Mice Rice University

4. 7 Blind Mice Rice University

5. 7 Blind Mice Spear Cliff Fan Pillar Rope Rice University

6. 7 Blind Mice Cognitive Wireless Rice University

7. Cognitive Wireless • Hype or Next Big Thing ? • Feasibility ? • Extent of Utility ? • Impact as big as we will like to believe ? • Scientific questions • Relevant problem formulations • Platforms as technical demonstrators Rice University

8. Outline • Testbeds/Platforms [7 minutes] • TFA • WARP • Thought Experiment to a Demo [10 minutes] • Stealing from an ongoing flow • Formulation • Result & protocol Rice University

9. At-scale: TFA-Rice Mesh Network • In low-income neighbourhood of Houston, Texas • TFA Charter: To empower with technology • Deployed: 4000+ real users over 4 Km2 Rice University

10. At-scale: TFA-Rice Mesh Network • Current TFA speeds peak at 0.5 Mbps/user • Goal: 4-10X gains • At-speed: Use WARP for a clean-slate network WARP Rice University

11. Wireless open-Access Research Platform • WARP • Programmable FPGA platform (Virtex IIPro, Virtex 4) • High-end MIMO (upto 4x4, 60-100 Mbps) • Frameworks for clean-slate designs Rice University

12. Wireless open-Access Research Platform • Multiple Design Flows • WARP + Matlab = WARPLab (offline design) • Simulink + Sysgen = WARP_Phy + WARP_MAC (real-time) • Control & Management Plane = WARPnet (deployed networks) Rice University

13. WARP Users Rice University

14. WARP Users (by end of Summer’08) Industry (11) Academia (15) • Xilinx (3 sites) • Nokia Beijing • DRS Signal Solutions • Spectrum Signal Processing • Irvine Sensors • ASTRI (Hong Kong) • Communications Research Centre • Motorola Bangalore • Microsoft Research Beijing • Toyota Info. Tech • Ericsson Research • UCSD • UC Irvine • USC • Polytechnic • Rutgers • University of Waterloo • University of Oulu • Nile University • RWTH Aachen University • University of Klagenfurt • UC Riverside • UOIT • UC Santa Cruz • Drexel University • UIUC Rice University

15. Applications • Urban-scale mesh network deployments (TFA-Rice) • Camp & Knightly, Infocom’08 • MIMO : Sphere detection/decoding • 3G-LTE, WiMax, 802.11n (Cavallaro’s group) • PM protocols for low-power handsets • Liu and Zhong, Mobisys’08 • Cooperative communications • Random Access Cooperative Systems (Tech Report, Asilomar’08) • Cognitive wireless (today) Rice University

16. Purpose of a Testbed • Verify a concept • Sanity check & feel good • Engineering approximation error • Uncover surprises • Overhead multiplier effect observed in TFA • 50X reduction in capacity due to routing packets • Need at-scale and at-speed systems for such discoveries • Thought Experiment • Mantra is “I will build” • Forces you to start with the correct setup Rice University

17. Outline • Testbeds/Platforms [7 minutes] • TFA • WARP • Thought Experiment to a Demo [10 minutes] • Stealing from an ongoing flow • Formulation • Result & protocol Rice University

18. Two-Flow Network Primary Objective: maximize rate Rs Constraint: cannot reduce primary’s rate Rp Rs Secondary Rice University

19. Rate Region Primary • Since interfering links, tradeoff between their rates • True for any choice of protocols Cp Rp Rp Rs Secondary Rs Cs Rice University

20. Rate Region hpp • The whole region depends on topology • Topology = {hpp , hss , hps , hsp , …} • If region is known, then rate Rs is easy to find. Cp Rp hps Rp hsp Rs hss Rs Cs Rice University

21. Key Issue: Lack of Knowledge Primary • Compound Network: The secondary does not know • the topology • Rp • How can it select the Rs ? Cp Rp Rp Rs Secondary Rs ? Cs Rice University

22. Without Help, Secondary Cannot Send • Without any knowledge, max Rs= 0 • Solution = Cognition • Snoop to learn • What can one learn about this region ? Rp Rs Rice University

23. Information Content in Snooping • Hear and decode all transmissions • Estimate primary rate, Rp • eg. by listening to ACKs • Estimates are never perfect • Overhearing over noisy wireless channels Primary Rp Rs Secondary Silent Rice University

24. Information Content in Snooping • Not sufficient information to estimate the region • Reason: Passive estimation • No feedback with primary • Solution: Estimation by perturbation Primary Rp Rp Rs Secondary Silent Rs ? Rice University

25. Estimation by Perturbation • Key requirement: Primary should be adapting its rate to network conditions (e.g. TCP) • Feedback increases compound network capacity Rp + Rs Rs Snoop Rice University

26. Estimation by Perturbation • Inject packets at a small rate • See if the primary is affected • If not, increase rate till it does • Then adjust Primary reacts here Rp Rs Rice University

27. Protocol Trajectory • Slow start • Adapt its rate to find optimal rate • Tunable parameters, Ttransmit, Tsense, Rs • Work in progress: characterize convergence rate R*s Secondary rate Ttransmit time Tsense Rice University

28. R*s Rs Demo on WARP • Primary flow alternating between high and low data rates • Secondary (estimation by perturbation) Rp Secondary rate time Rice University

29. R*s Rs Demo on WARP • Primary flow alternating between high and low data rates • Secondary (estimation by perturbation) • Loss = [R*s(t)-Rs(t)]dt Rp Secondary rate time Rice University

30. Lesson I: Starting Point • Model as if you will build it • No network information is available • Everything has to be estimated • Directly implementable without any rework • Prototype demo using WARP • Work by Scott Novich Rice University

31. Lesson II: Lack of Information • Hard to steal from dumb devices (e.g. walkie talkies) • They do not react to increased interference • Easier to steal from “smart systems” • Allows one to observe their behavior by perturbing them Rice University

32. Recap • Prototyping useful at many levels • Discovering surprises (TFA Network) • Thought experiment (this talk) • Sanity check (demo later) • Distributed cognitive wireless • Stealing from dumb devices not possible • Intelligently stealing from smart devices possible Rice University

33. Questions ? WARP: http://warp.rice.edu TFA: http://tfa.rice.edu CMC: http://cmc.rice.edu Rice University