4514 Project 1

This assignment is intended to introduce you to Data Link layer. You are to implement the programs described below on any CCC DEC machines.

You are to write two programs that simulate services provided by a simple Data Link layer. The two programs are:

• stuff - "receives packets" from the network layer, frames them, adds an appropriate parity bit, and "sends bits" to the physical layer.

• unstuff - "receives bits" from the physical layer, pulls out the frames, checks the parity, and "sends packets" to the network layer.

You will use a parity bit for single bit error detection. You must use EVEN parity.

The simulated interfaces between the physical layer and network layer are stdin and stdout, as appropriate. For example, stuff reads from stdin (network layer) and writes to stdout (physical layer).

Both stuff and unstuff should stop reading and exit when they encounter EOF from stdin.

Important! You must follow these details:

• stuff will assume there is 1 packet per line. It sends each packet in a separate frame.
• You must use 011110 as the frame boundary.
• stuff does not transmit newlines ('\n'), even after the last frame (see examples below).
• unstuff places a newline after each packet.
• You must append the parity bit after the frame boundary. You should check parity on the data (with stuffed bits) only, and not on the frame boundary.
• Your programs must handle lines of 80 characters (or fewer).

You can use Unix pipes and filters to make debugging your pair of programs easier. For example:

   cat data1 | stuff | unstuff > data2

There are numerous ways to obtain bit information. However, here is a sample that does a bit-mask looking at each bit in a long integer that you are free to use and modify:

/* print out the bit information of the long integer passed in */
void printBits(int c) {
   int i;			/* loop index */
   int mask;			/* for checking for each individual bit */

   /* set the mask to have a 1 in the furthest bit left, rest 0 */
   mask = 1 << 15; /* 10000000 */

   /* each char is 1 byte = 8 bits */
   for (i=1; i<=16; i++) {

      /* is the bit a 1 or a 0? */
      if (c & mask)
	 printf("1");
      else
	 printf("0");

      /* shift the mask to the next bit down */
      mask >>= 1;

      /* but a space between bytes */
      if (i%8==0)
	printf(" ");
   }

   return;
}

A few recommendations on completing this lab if you find yourself struggling (in order):

1. Convert a single char on stdin to bits.
2. Convert multiple chars on stdin to bits.
3. Stuff bits.
4. Add frame ending.
5. Repeat for unstuff.
6. Polish, clean-up, debug thoroughly ...
7. Work on making it faster.
8. Turn it in.
9. Relax!

Remember, do each step thoroughly. Make sure the step you are on works well and you understand it before going to the next step.

There will be a series of longer test cases released shortly before the project is due (so as not to give you a chance to optimize your project for the test cases. :-) ). However, some minimal test cases you should get working are:

hello
world

claypool@saagar=>> cat a
a
claypool@saagar=>> cat a | stuff
011000010111101claypool@saagar=>> 
claypool@saagar=>> cat abc
abc
claypool@saagar=>> cat abc | stuff
0110000101100010011000110111100claypool@saagar=>> 
claypool@saagar=>> cat abc | stuff | unstuff
abc
claypool@saagar=>> cat test2
abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLNOPQRSTUVWXYZ1234567890!@#$%^&*()
The
quick
brown
fox
jumped
over
the
lazy
dogs.
We the people of the United States, in order to form a more perfect union...
She saw sea shells at the seashore.
claypool@saagar=>> cat test2 | stuff
0110000101100010011000110110010001100101011001100110011100110100001101001011010100110101101101100011011010110111000110111010111000000111000010111000100111000110111001000111001010111001100111001110011101000011101001011101010010000010100001001000011010001000100010101000110010001110010010000100100101001010010010110100110001001110001001110101010000010100010101001001010011010101000101010101010110010101110010110000101100101011010001100010011001000110011001101000011010100110110001101110001110000001110001001100000010000101000000001000110010010000100101010111010001001100010101000101000001010010111100010101000110100001100101011110001110000101110010101101001011000110110101101111000110001001110001001101110101110011100110111000111100011001100110111010111010000111100011010100111001010110110101110000001100101011001000111100011011101011100110011001010111000100111101011100100011010000110010101111010110110001100001011101010011101001011110101100100011011101011001110011100011001011100011110101010111001100101001000000111001000110100001100101001000000111000000110010101101110101110000001101100011001010010000001101110101100110001000000111001000110100001100101001000000101010101101110001101001011100100011001010110010000100000010100110111001000110000101110010001100101011100011001011000010000001101001011011100001000000110111010111000100110010001100101011100010001000000111001000110111010010000001100110011011101011100010011011010010000001100001001000000110110101101110101110001001100101001000000111000000110010101110001001100110011001010110001101110010000100000011100101011011100011010010110111010110111000010111000010111000010111000111101010100110110100001100101001000000111000110110000101110011100010000001110001101100101011000010010000001110001101101000011001010110110001101100011100011001000000110000101110010000100000011100100011010000110010100100000011100011011001010110000101110001101101000011011101011100010011001010010111000111100claypool@saagar=>>
claypool@saagar=>> cat test2 | stuff | unstuff > temp
claypool@saagar=>> cat test2 | stuff | unstuff > temp
claypool@saagar=>> diff temp test2
claypool@saagar=>>

A bonus of 10 points will be rewarded to the group that has the fastest overall stuff and unstuff times. The test cases used for this performance test will be announced later.

The main information I'd like you to have from the documentation standard is; author, date, project id, language, OS dependencies, description and building information. All this information should appear in a README file that accompanies your program.

Here is a sample of the information you should have:

Author:                         Mark Claypool
Date:                           1/21/99
Project ID:                     Project 1
CS Class:                       CS4514
Programming Language:           C
OS/Hardware dependencies:       None

Problem Description:            This program implements blah, blah, blah

How to build the program:       make