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.
- 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.
- 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.
- 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.)
- Estimate the expense, the time, and the sequence
of steps needed to get a domain name and a hosted web-site with that name.
- 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.
- Send an email to msande130-aut0506-staff AT lists.stanford.edu
using telnet. [0 points, but compulsory.]