College of Computer Science

Northeastern University

COM1337-3501: Computer Communication Networks

 

Spring 2002

May 20th, 2002

 

Assignment 3-4 (due May 30th, 2002).

Each problem is worth 10 points.

 

 

1.                 Given the following network, build step by step the routing tree starting from node A. Use Dijkstra’s algorithm and show the value of M, and C(n) at each step.

 

2.                 What is the sequence of exchanged message to open a TCP connection between two hosts H1 and H2.

 

 

3.                 Suppose a TCP connection has a window size of eight segments, an RTT of 800ms. The sender sends segments at a regular rate of one every 100ms, and the receiver sends ACKs back at the same rate without delay. A segment is lost, and the loss is detected by the fast retransmit algorithm on the receipt of the third duplicate ACK. At the point when the ACK of the retransmitted segment finally arrives, how much total time has the sender lost (compared to a lossless transmission) if:

a.         The sender waits for the ACK from the retransmitted lost packet before sliding the window forward again?

 

 

 

 

 

 

 

 

 

 

 

 

 

b.        The sender uses the continual arrival of each duplicate ACK as an indication it may slide the window forward one segment?

 

 

 

 

 

 

 

 

 

 

 

4.                  In TCP state-transition diagram, why can’t we go from CLOSING state to Closed state immediately after receiving the ACK message (what is the reason for having the TIME_WAIT state)?

 

 

5.                 Textbook Chapter 5, Exercise 28, page 439.

 

 

 

 

 

 

6.                 Explain the idea underlying TCP Vegas.

 

 

 

 

7.                 Describe the Tspec of the following flow using the token bucket model:

 

 

8.                 On an Ethernet LAN, a node A is sending a multicast packet to IP multicast group: 239.0.0.1. What is the Ethernet destination address that is used by the sender?

 

 

9.                 The following network is using DVMRP as the multicast routing protocol. The multicast group has one sender and two receivers. Show all the prune messages. Show the resulting multicast-tree.

 

 

10.             Consider an MBone formed on top of the following network. The MBone is made of the following tunnels: (R1, R3), (R1, R4), (R3, R5). Only R1, R3, R4, and R5 are running DVMRP over the MBone.

a.          Show the final multicast-tree.

b.         Assume that the multicast group IP address is 239.0.0.1, and that the routers have IP addresses: R1: 129.10.118.1, R2: 129.11.118.1, R3: 129.12.118.1. What are the src/dst addresses of the packet sent from the sender to R1? Describe how this packet is forwarded by R1 (header information)?