Assignment 5: Simulating The Data Link Layer

Assigned: Friday, March 3, 2000
Due: Wednesday, March 15, 2000

In this assignment, you will work as a class to simulate the error-detection and frame alignment aspects of the data-link layer. For convenience, the portions that deal with the simulated bits sent and received will use character '0' for a zero bit and character '1' for a one bit.

Here are the programs that you will need to write to support the simulator. We'll have them run as separate Unix processes.

• bitsToChars: converts the actual bits received on standard input to the ``character-bit'' representation. For example, on input of Abc this will give an output of something like 010000010101001101010100.
• frameXXX: puts the character-bits from standard in put into frames. XXX can be ByteStuff, BitStuff, or ClockBased.
• addPrefix: adds a random-length character-bit prefix to the input
• addNoise: takes a character-bit representation on standard input and flips some percentage of errors (specified on the command line) before sending to standard output
• unframeXXX: reads character-bits from standard input, identifies frames, discards erroneous frames (with an accompanying error message printed to stdout) and sends to contents of the successful frames to standard output.
• charsToBits: undoes bitsToChars

In addition, the frameXXX and unframeXXX need to be able to add error-detection codes to the payload. They will rely on two helper functions,

• char *addcodes(char *data), which builds a new string that adds the error-detecting bits, and
• int checkbits(char *extendedData), which returns 1 if the error-detection scheme detects no error and 0 if it detects an error.

Using these programs together, I can see how well the bit-stuffing algorithm does with 1 bit error out of 100 with somethinn like:

% cat example | bitsToChars | frameBitStuff | addPrefix 50 | \
      addNoise .001 | unframeBitStuff | charsToBits

Please use class on Wednesday, March 8, and Friday, March 10, to coordinate within and between groups. Attendance those days is mandatory.

The group assignments are as follows:

bitsToChars and charsToBits

• Jarrod Routh and Dima Krivin,

addPrefix and addNoise

• Alex Brown and Jon Flaherty

addcodes and checkbits using CRC-16

• Wanlin Liu and Erik Hanson
• Amit Nangalia and Oleksiy Andriychenko

addcodes and checkbits using two-dimensional parity and a row size of eight

• Sarah Luebke, Todd Holloway, Dorene Mboya and Erin Nichols
• Nathan Corvino and Joe Simonson

frameBitStuff and unframeBitUnstuff

• Eric Otto and Andrew Vick
• Brian K. Smith and Josh Vickery

frameByteStuff and unframeByteUnstuff

• Jared Baszler and Andrew Kensler
• Chris Kern and Rackham Hoke

frameClockBased and unframeClockBased

• Pete Broadwell and Dan Hawando
• Joey Lesh and Joe Pipkins

Additional Notes: