Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1 ECSE-4963: Experimental Networking Exam 1 Time: 60 min (strictly enforced) Points: 50 YOUR NAME: Be brief, but DO NOT omit necessary detail {Note: Simply copying text directly from the slides or notes will not earn (partial) credit. Brief, clear and consistent explanation will.}

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2 I. Quick questions on probability/experiment design 1. [5 pts] What is the difference between the cumulative distribution function (CDF) and probability density function (pdf)? State one purpose where CDF is easier to work with than the pdf ?(hint: mean vs median)

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3 I. [10 pts] Show (derive) that if two random variables are independent {I.e. P(XY) = P(X)P(Y)} they are uncorrelated {I.e. E(XY) = E(X)E(Y) }, but the reverse is not true.

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4 2. [10 pts] Given: n=6 random RTT samples (in ms): {31, 42, 28, 51, 28, 40} q Find: sample mean (xbar), sample standard deviation (s), 90% confidence interval (CI) & 95% CI for the population mean

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5 II. [10 pts] Experiment Design: Analyze the 2^3 design a) Quantify all the main effects and all interactions [5 pts] b) Quantify percentages of variations explained [3 pts] c) Sort the variables in the order of decreasing importance [2 pts] A1A2 C1C2C1C2 B B

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7 I. [15 pts] DESIGN WALK-THROUGH: We learnt about animation, simulation (ns-2), graphing tools, and click modular router toolkit. Assume that you are given the following design problem: to design a new error resilience protocol for overlay networks that involves a mix of forward error correction (FEC) and automatic repeat request (ARQ) to be implemented at the IP-layer (I.e. layer 3). a) Discuss the design issues and tradeoffs for this problem [4 pts] b) Walk me through how you would systematically use the above tools (in the right sequence) to help design and incrementally refine your design. [5 pts] c) What metrics would you use to test/validate your protocol & explain why your set of metrics is a complete and meaningful set. [3 pts] d) What set of workloads would you use to test such a system & explain why it is meaningful, and yet helps you make quick progress in your design process. [3 pts]

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8