1. USC-TPWN, May 20-21, 20081 What constitutes a useful experimental result? Bhaskar Krishnamachari Ming Hsieh Department of Electrical Engineering USC Viterbi School of Engineering

2. 2 Two kinds of useful experimental results Translating theory to practice Going beyond current practice

3. 3 Translating Theory to Practice From theoretical algorithms to working systems Provide Working examples of: –Cross-layer optimization, backpressure algorithms, etc. Rarely a trivial task: –Do the abstractions hurt performance in practice? –Do protocols converge despite packet losses, random delays? How do they have to be changed to make them work in practice?

4. 4 An Example The following iterative message-passing algorithm can be formally proved to converge to a max-min fair rate allocation for a given wireless sensor-network data gathering tree Sridharan, Krishnamachari, 2008.

5. 5 Translating to Practice MMF-RC provides max-min fair rate allocation under an idealized setting: synchronous environment, global coordination, static flows, perfect links In the real world – need to figure out how to estimate rates, provide distributed operation, handle asynchrony, dynamic flows, imperfect links

6. 6 Solution: WRCP, inspired by MMF- RC Has a lot of “hacks” to ensure convergence and efficiency empirically – no simple analytical characterization

7. 7 Going beyond current practice Beyond off-the-shelf hardware This is the missing link in our field; one reason for disconnect between physical layer and networking researchers

8. 8 Example With idealized cooperative flooding (perfect channel information, coherent combining), can show that the time to get information to all nodes is logarithmic in the diameter How does this translate to practice?

9. 9 Claim We do not have enough principled experimental researchers in our field that can talk to, understand theorists.