Virginia Tech

Department of Computer Science

CS6504 Mobile Computing

Spring 2007

 

Homework 3 (Total 40 pts)

Due in class on Wednesday February 21st, 2007

 

Please answer the following questions using your own words.

 

Q1. (10 pts) Explain how CSMA/CD and CSMA/CA answer the following questions

·        When should the station access the medium?

·        What should be done if the medium is busy?

·        How should the station determine the success or failure of the transmission?

·        What should the station do if there is an access conflict?

 

Q2. (10 pts) Explain how MACA solves the hidden terminal problem, as well as the exposed terminal problem.

 

Q3. (10 pts) Explain how MACAW ensures reliable data delivery by the link-layer.

 

Q4. (10 pts) Explain how PCF and DCF coexist in IEEE 802.11 MAC sub-layer.