Homework 4 - Chapter 4

Due: Friday May 11, 2007 at 5pm

Each question is worth 2 points.

  1. Describe how the delay and throughput would differ between pure ALOHA and slotted ALOHA under the following conditions. Which would be higher? Explain why.
    1. Low load (few stations transmitting)
    2. High load (many stations transmitting)
  2. Draw the Manchester and differential Manchester encodings for 01100011.
  3. Two half-duplex Ethernet stations are contending for the channel. What is the mean number of contention slots for these two stations?
  4. You are designing a network that will use CSMA/CD for contention. The physical media has the following characteristics: 1.5Mbps, signal speed is 2/3rds the speed of light and maximum cable length is 500m.
    1. How long would the contention slot have to be?
    2. What would be the minimum frame size (i.e. how long would a frame have to be so it takes longer to transmit than the length of a contetion slot)?
  5. How does Fast Ethernet have the same minimum frame size as regular Ethernet even though it transmits 10x faster?
  6. Under what circumstances might two or more wireless stations using MACA contention resolution transmit at the same time?
  7. Would it be possible for any of the 802.11 protocols to use CSMA/CD (like Ethernet) instead of CSMA/CA for channel contention? Explain why or why not.
  8. Assume an 802.11g is transmitting 128 byte frames back-to-back at its maximum rate of 54Mbps. If each bit is flipped with a probability of 1x10-6, how many frames per second will be damaged on average?
  9. Can a Bluetooth device be in multiple piconets at once? If so, can it act as master in more than one piconet?
  10. When using a spanning tree algorithm to determine the topology for bridges, why might one leave bridges in place that are not used in the current spanning tree?