Quiz 1

CS/EE 555

Fall 2001

September 21, 2001

 

The quiz is open-book, open-notes, closed neighbor. 25 Minutes. Show all your work.

 

  1. (10) Consider an 80 kb/s network link connecting the earth to the moon. The moon is about 1.5 light-seconds from earth. If 1-Kbyte packets are sent over this link using a stop-and-wait algorithm for reliable delivery what data transfer rate can be achieved?




    (10) If instead, a sliding-window algorithm is used for reliable delivery, what data transfer rate can be achieved assuming that errors are infrequent.




    (10) What is the minimum number of bits required in the packet sequence number field to be able to achieve this rate?




  2. (10) Consider the CRC divisor polynomial  and the message 101101. What is the sequence of bits corresponding to the message with the appended CRC?







    (5) Is this CRC divisor polynomial able to detect any odd number of errors in the received bit string? Why or why not?








  3. (10) Consider the virtual circuit network:


    with virtual circuit tables mapping, in both directions, input (port, VCI) to output (port, VCI) as follows

 

Input/Output

Output/Input

(Port,VCI)

(Port,VCI)

(1,2)

(3,1)

(1,1)

(2,3)

(2,1)

(3,2)
 

Input/Output

Output/Input

(Port,VCI)

(Port,VCI)

(1,1)

(3,3)

(1,2)

(3,2)

 

 
 

Input/Output

Output/Input

(Port,VCI)

(Port,VCI)

(1,3)

(2,1)

(1,2)

(3,1)

 

 

List all endpoint to endpoint connections in this network.