Homework #3
  Homework #3.
Due 11:45PM, Apr.13, 2016 Wednesday.
 
   Problems  
 
please answer the following problems for the chapter 3 of the text:
  1. The following data fragment occurs in the middle of a data stream for which the byte-stuffing algorithm described in the text is used: A B ESC C ESC FLAG FLAG D. What is the output after stuffing?
  2. Data Link protocols almost always put the CRC in a trailer rather than in a header. Why?
  3. A channel has a bit rate of 4 kbps and a propagation delay of 20 msec. For what range of frame sizes does stop-and wait give an efficiency of at least 50 percent?
  4. Frames of 1000 bits are sent over a 1 Mbps channel using a satellite whose propagation time from the earth is 270 msec. What is the maximum achievable channel utilization for stop-and-wait? The above example network is typical so-called long fat network (LFN), what are your proposals to improve the efficiency of LFN?
  5. What is the difference between a datalink(Logical Link) and a physical link?
  6. what is the difference between Error Control and Flow Control in datalink layer.
  7. How do sliding window protocols improve communication performance when compared to stop-and-wait protocol.
  8. In protocol Go-back-n with a 3-bit sequence number, How big can the sender's window size be? How come?
  9. In protocol Selective-Repeat with a 3-bit sequence number,  assume the sender and the receiver have same window size,  How big can the sender's windows size be? Why?
  10. Frames of 1000bits are sent over a 1-Mbps channel using a geostationary satellite whose propagation time from the earth is 270ms. Acknowledgements are always piggybacked on to data frames. The headers are very short. Three-bit sequence numbers are used. what is the maximum achievable channel utilization for
    (a) Stop-and-wait
    (b) Go-back-n
    (a) Selective-repeat
  11. In the Internet, what are the situations in which PPP plays a major role?
  12. What is the minimum overhead to send an IP Packet using PPP? Count only the overhead introduced by PPP itself, not the IP header overhead.
  13. Does PPP provide reliable data transfer using sequence numbers and acknowledgments?  if not, think about which layer will deal with frame errors?
  14. What kinds of services can data link layer possibly provide to the network layer? if all the data link layer in the Internet can provide reliable service, is it necessary that the upper layer like transport layer also provide reliable transmission service?
 
  Notes for Submission  
  You must follow the Electronic Submission Guidelines to submit HW3.
You can create your submission by doing the following for e-submission:
  • 1. Create a file containing your answers
  • 2. mail this file to classmail, name the mail subject according to the Guidelines