COMP 361 Tutorial 8

More Problems  of Chapter 3

 

Last revised: Monday, 28. March 2005 01:12 +0800

Problem 1:

Refer to Figure 3.53 of the book (p. 116 of the slides)  that illustrates the convergence of TCP's additive increase, multiplicative decrease algorithm. Suppose that instead of a multiplicative decrease, TCP decreased the window size by a constant amount. Would the resulting additive increase additive decrease converge to an equal share algorithm? Justify your answer using a diagram similar to Figure 3.53.

 

Problem 2:

Consider the following plot of TCP window size as a function of time.

 

Assuming TCP Reno is the protocol experiencing the behavior shown above, answer the following questions. In all cases, you should provide a short discussion justifying your answer.

  1. Identify the intervals of time when TCP slow start is operating.
  2. Identify the intervals of time when TCP congestion avoidance is operating.
  3. After the 16th transmission round, is segment loss detected by a triple duplicate ACK or by a timeout?
  4. After the 22nd transmission round, is segment loss detected by a triple duplicate ACK or by a timeout?
  5. What is the initial value of Threshold at the first transmission round?
  6. What is the value of Threshold at the 18th transmission round?
  7. What is the value of Threshold at the 24th transmission round?
  8. During what transmission round is the 70th segment sent?
  9. Assuming a packet loss is detected after the 26th round by the receipt of a triple duplicate ACK, what will be the values of the congestion-window size and of Threshold?

Problem 3:

Consider the TCP flow control algorithm presented in the slides. The Receiver sends the sender a value RcvWindow which is the spare room (in bytes) in the RcvBuffer.  The sender responds by using the value of RcvWindow to limit the number of bytes it sends out. Explain why this  guarantees that the RcvBuffer in the receiver will never overflow.


 

Problem 4:

Consider the three way handshake in TCP connection setup. Suppose that an old SYN segment from host  A arrives at host  B, requesting a TCP connection. Explain how the three-way handshake procedure ensures that the connection is rejected.