MS&E 130/231: Information Systems, Autumn 2005-06

Instructor: Ashish Goel

Handout 3: Homework 2. Given 10/14/05. Due 10/21/05.



Since there is no class on 10/21, please slip your HW under my door before noon. We will start handing out solutions starting 1 pm, so we will not accept any late submissions.


Collaboration Policy: You are allowed to discuss general strategies for solving a problem with other students in the class, and also to clarify your understanding of the problem. You are not allowed to copy or see somebody else’s homework.


  1. State some of the reasons why an application developer might choose to run an application over UDP rather than TCP. Please be brief and precise.
  2. Suppose the window size of a TCP connection is artificially fixed to 2, and its timeout value is artificially fixed to 200ms. Assume a constant RTT of 100ms. Further, assume that every third data packet sent out gets lost (regardless of whether it is a retransmission or a first-time packet), and that every third ACK sent out gets lost. Describe the sequence of events for transmitting 4 packets from sender A to receiver B, and give the time to complete the transfer. Assume that the receiver stores out of order packets for future use. Ignore advanced features such as fast retransmit that we did not discuss in class. The transfer is considered complete when the sender receives an ACK indicating that all packets have been successfully transmitted.
  3. Consider a reliable data transfer protocol that uses only negative acknowledgements (NAKs). Suppose the sender sends data only infrequently. Would a NAK only protocol be preferable to one that uses only ACKs? Why? Now suppose the sender has a lot of data to send and the rate of packet loss is very small. In this second case, would a NAK-only protocol be preferable to a protocol that uses only ACKs? Why? (Problem 3.11 from the text.)
  4. Estimate the expense, the time, and the sequence of steps needed to get a domain name and a hosted web-site with that name.
  5. Suppose you have a basic AIMD (additive increase, multiplicative decrease) implementation of TCP – each time all the packets in a window get successfully acked, the window size increase by one. When there is a packet drop, the window size is halved. If a TCP connection suffers a packet loss every 10th packet, what is the rate at which it transmits? Assume a fixed RTT and a fixed timeout of 100ms, a packet size of 1KB, and assume that no ACKs get lost.
  6. Send an email to msande130-aut0506-staff AT using telnet. [0 points, but compulsory.]