College of Computer Science

Northeastern University

COM1337-3502: Computer Communication Networks

 

Spring 2002

April 25, 2002

 

Assignment 2 (due May 6th).

 

 

 

Problem 1 (20 pts):

  1. Consider the framing mechanism based on bit-stuffing and using flag 01111110. Build the frame corresponding to the following sequence of bits:

010110001111100111111

 

 

 

 

 

  1. Consider the character-based framing mechanism. Build the frame corresponding to the following sequence of characters (assume no Header is used):

Data Packet = A C B STX D DLE G DLE ETX A DLE DLE

 

 

 

 

 

Problem 2 (30 pts):

Let g(X) = X4+X+1 be the generator polynomial used for CRC generation.

  1. Draw the circuit that can generate the CRC (in hardware).

 

 

 

 

 

 

 

 

  1. Using the hardware circuit, compute the CRC of the data stream S = 0 1 0 1.

 

 

 

 

 

 

 

 

 

  1. Compute the CRC using polynomial division.

 

 

 

 

 

 

Problem 3 (5 pts):

Assume that we are using an Automatic Repeat reQuest (ARQ) protocol, where the Sender-Window-Size (SWS) is equal to n, and the Receiver-Window-Size (RWS) is equal to 1. What should be the constraint on MaxSeqNum

 for the the protocol to work correctly?

 

 

 

 

 

Problem 4 (10 pts):

 

Given the extended LAN shown in the following figure, indicate which ports are selected by the spanning algorithm?

Figure 1. Which ports are selected by the spanning tree?

 

Problem 5 (20 pts):

 

In 10Mbps Ethernet, the minimum packet size is defined as the number that could be transmitted during a RTT (51.2 ms).

· What is the minimum packet size?

 

 

· What is the reason for this minimum packet size?

 

 

 

· How can we extend Ethernet to a data rate of 100Mbps while keeping the same minimum packet size?

 

 

 

Problem 6 (10 points):

 

Apply the Bellman-Ford’s algorithm to compute the shortest path from any node u to node F in the following graph. Assume the given initial values.

A

¥

 

 

 

 

 

 

 

 

B

1

 

 

 

 

 

 

 

 

C

¥

 

 

 

 

 

 

 

 

D

¥

 

 

 

 

 

 

 

 

E

¥

 

 

 

 

 

 

 

 

F

0

 

 

 

 

 

 

 

 

 

 

Problem 7 (5 points):

Give two examples of:

 

Indicate the host part and network part of the IP address.