1. If the bit string 0111101111101111110 is to be bit stuffed according to the rules discussed in class, what is the output string?

2. A bit stream 01001110110 is transmitted using the standard CRC method. The generator polynomial is x^{3}+1. Show the actual bit string transmitted. Now, suppose the third bit from the left is inverted during transmission. Show that this error is detected at the receiver's end. Describe an error that could occur that would not be detected.

3. It takes 40 msec to send a frame and 5 msec to send an acknowledgement. The propagation delay is 200 msec in the ``forward direction'' and 20 msec in the ``reverse direction''. Processing time of any data is negligible. How many complete frames can are sent before an acknowledgement is received (assume no loss in the channel)? Using stop-and-wait, what is the channel efficiency?

4. A channel has a bit rate of 4 kbps and a propagation delay of 40 msec. For what range of frame sizes does stop-and-wait give an efficiency of at least 50 percent?

5. Describe the circumstances in which pure ALOHA performs better than slotted ALOHA.

6. Describe the circumstances in which 1-persistent CSMA is better than p-persistent CSMA.

7. Why is there a minimum frame length for Ethernet? Why is there a maximum frame length for Ethernet?
   
   
   

   For the next set of questions, you will likely need to do some surfing on the Internet. Here are a couple of useful links:

   • http://www.networking.ibm.com/mse/mse0c01.html
   • http://www.compnetworks.com/solutions_ethernet.htm

8. Why is bandwidth to the client likely to increase when a shared Ethernet LAN is replaced by switched Ethernet LAN?

9. Suppose a client expects to see a 10 fold increase in bandwidth when the client's shared Ethernet is replaced by a switched Ethernet. Describe a scenario in which the client's expectations are not met (i.e., the client sees minimal increase in bandwidth).
   
   
   

   For the next set of questions, you will likely need to do some surfing on the Internet. Here are a couple of useful links:

   • http://alpha.fdu.edu/~kanoksri/IEEE80211b.html
   • http://www.intelligraphics.com/articles/80211_article.html

10. Describe two properties of the wireless environment that are not present in the wired environment (i.e., why do we need different protocols for wired and wireless networks?).

11. 802.11 can operate in infrastructure mode or in ad hoc mode. Describe a scenario where infrastructure mode would be used. Describe a scenario where ad hoc mode would be used.

12. Why is security such a big concern for wireless networks?

13. Suppose you were deploying a network in your house/apartment/dorm room. What would be an advantage to deploying a wired network? What would be an advantage to deploying a wireless network?