CSE 494/598 Wireless Sensor Network
Homework Assignment 4 (100 Points)
Due on 19th April 2005 at the start of the class. No late submissions will be
accepted. No plagiarism. Answers should be written in proper English.
1. (40 points) To answer this question use “RMST: Reliable Data Transport in Sensor
Networks” by F. Stan and J. Heidemann, and “PSFQ: A reliable transport protocol for
wireless sensor networks” by C. Wan, A. T. Campbell and L. Krishnamurthy
a. RMST and PSFQ are two transport protocols for wireless sensor networks.
Compare the features of each and discuss the relative merits and demerits.
b. Suppose we want to provide source authentication and encryption in sensor
networks, at the transport level. Which protocol (RMST or PSFQ) would be easier
to modify to include the security features?
2. (30 points) To answer these questions use “Combs, Needles, Haystacks: Balancing Push
and Pull for Discovery in Large-Scale Sensor Networks” by X. Liu, Q. Huang and Y. Zhang
a. What are the differences between push and pull based strategies?
b. The authors propose a static and adaptive strategy that combines both push and
pull based strategy. Explain in detail with an example how they work.
3. (30 points) If a user sends a query to sensor networks, he/she could encounter the
following problems:
a. The query gets lost during the transmission because of unreliable links;
b. A sensor node receives the same query more than once, because the broadcast
nature of the query propagation.
c. If the results can be reused among different queries, it would be wasting time and
effort to try to get the same results from the sensor nodes that generate the
original data, that is, a better way would be cache the results in some easy-to-
reach nodes. But then the problem is how to keep the cached results up-to-date.
Directed diffusion explained in “Directed diffusion for wireless sensor networks” is one
possible way to address these problems. Explain how direct diffusion answers these
problems? What are other approaches in the literature?