CS332 (Prof. Szajda) Exam 2 March 27, 2003

Name:______

Note: This exam is closed book, closed note. You are to complete without the aid of your colleagues. The Honor Code applies.

Please be succinct and precise. All solutions must meet the Other Student Criteria (OSC). The Other Student Criteria means that a solution should provide enough written explanation so that another student in the class (who could not complete the assignment) could read the submitted material and, without asking questions, understand a correct answer.

Question 2 is worth 8 points. Question 11 is worth 20 points. All other questions are worth 6 points.

  1. Why exactly is the problem of finding the “minimum” path so difficult when using policy-based routing?
  1. Describe the advantages and disadvantages of statically populating forwarding tables versus dynamically populating forwarding tables.
  1. Tim Griffin explains that IP routing protocols do not dynamically route around congestion. Since it seems that this would be a natural thing to do, why isn’t it done in practice?
  1. What exactly is a “peering relationship”? If all peering relationships in the Internet were ended, what effects would this have on the Internet and why?
  1. Why is information gained from BGP not simply injected into intradomain routing protocols (for example as extra entries in the routing table)?
  1. Explain the following slide.

  1. Describe in some detail that path that a packet takes as it travels from sender to receiver through the Internet.
  1. UDP is an unreliable transfer protocol that essentially just provides multiplexing/demultiplexing on port numbers. Give three reasons why we don't simply force all applications to use TCP instead, since it can provide the same functionality to any app that normally uses UDP.
  1. (6 points) Explain the significance of the bandwidth  delay product as it relates to a link layer sliding window protocol. Be sure to explain the reasoning behind this relationship.
  1. (4 points) Explain how TCP guarantees in-order delivery. (Note: concern yourself with the in-order part, not the reliability part).
  1. (20 points) Consider the TCP header format given below. Describe the meaning (i.e. use) of each field. Although the individual flag bits are not shown, they are SYN, FIN, RESET, PUSH, URG, and ACK. Be sure to explain the use of all but the PUSH bit.

  1. (6 points) Explain carefully why so much care is put into setting TCP timeout values.
  1. (6 points) What is meant by the term additive increase/multiplicative decrease in the context of congestion control? Why is it used?
  1. (6 points) Describe the “fast retransmit” mechanism. That is, describe specifically how it works, and the specific problem it was intended to address.