Discussion Questions

Questions to discuss for the Macaw paper. Discuss any one of the issues listed below. Please post your response at http://hydralisk.cs.washington.edu.

  1. Although 802.11 supports RTS/CTS, most deployments of 802.11 turn it off. Why?
  2. How does performance in 802.11 networks (with or without RTS/CTS), vary as a function of access point placement and density? That is, if I have more users, can I simply add more access points? Why or why not?
  3. The MACAW paper uses simulations to study the performance of RTS/CTS for avoiding hidden and exposed terminals. When 802.11 adopted MACAW, however, people found the performance didn't always match what the simulations predicted. So: what simulation assumptions did the paper make, and are they unrealistic? what impact would it have on the results if they don't hold? For example, possible questionable assumptions might be: 0: The world is flat. 1: A radio’s transmission area is circular. 2: All radios have equal range. 3: If I can hear you, you can hear me (symmetry). 4: If I can hear you at all, I can hear you perfectly. 5: Signal strength is a simple function of distance. David Kotz and Calvin Newport and Chip Elliott. The mistaken axioms of wireless-network research. Technical Report TR2003-467, Dept. of Computer Science, Dartmouth College, July, 2003.
  4. How do you think the results in the MACAW paper would change if carrier sense was more sensitive than transmission? In practice, it is easier to tell if something is being sent, than to be able to correctly receive that transmission. What if the range for carrier sense was more than twice that of a valid transmission? Would that reduce the need for RTS/CTS?