CS 3413 Data Communications, Fall 2004 Assignment 4 Comments

This assignment had 10 questions, each worth 10 points.

The maximum score on this assignment is 100 points.

Problem number 10 was not graded. Everyone got credit for this problem.

Problem number 10 asked about the window in a sequential receive protocol. It was not clear that it was the sender's window that it was asking for although there was not enough information to tell what the receiver's window was. Also, the book did not make it clear how to distinguish between the frames that had been sent and net acknowledged, and those that had not yet been sent.

• Problem 2, number 6.9.
  A number of people set this up correctly but made errors in calculation.
• Problems 4 and 5, 6.10a and 6.12.
  Remember that you need to multiply the message polynomial by the highest power in the generator before division.
  It is easier to keep the bit positions straight if you use the polynomial representation than just using the bits unless you do it on graph paper.
• Problem 8, number 7.3.
  In this problem the propagation delay is given although it is unclear whether this is a one-way or round trip delay. It was probably supposed to be the round trip delay, since 240 ms is the round trip delay for a geosynchronous satellite.
• Problem 9, number 7.4.
  Start the problem by calculating the time between sending groups of three frames from A to B. Use this to find the data rate in bps.