# CS 125, Fall 2017 Computer Networks

## Homework 1—Network Parameters

Due: Monday, September 11, 2017

The purpose of your assignment is to help you understand some of the mathematical and numerical relationships between various network parameters. All of the problems are taken from the class textbook.

Please submit your answers on paper (preferably typed and formatted with LaTeX). The due date is the beginning of class on Monday, September 11, 2017.

In Chapter 1 of the book, do problems P6, P12, P14, P15, P16, P22 (first part), P24, P25, and P33. At the bottom of your submission, also estimate the amount of time you spent on this assignment.

Notes:

P14:
a is the rate of packets arriving at the link, in packets/second, as defined in P15.
P22:
Calculate the probability of successful reception. You are welcome to also find an expression for the number of retransmissions; if you do so, it is useful to recognize that a geometric random variable is involved.
P25:
An American football field is 100 yards long (actually 120 yards because of the two 10-yard end zones). A yard is about 0.91 meters. So a football field is 91 meters, or about 110 meters including the end zones.
P33:
You'll have to draw on your maxima/minima skills from calculus to solve this one. Think about how long it takes before the first bit of the last packet can be transmitted, and thus how long it takes the last packet to arrive at the destination through the two routers. Find an expression for the total time to get the whole file to its destination and then minimize that with respect to S.