aaalloc / CRC-IDECC

Introduction, Detection, and Error Correction on Content with CRC-8 / School project

CRC-IDECC

This a project school that consist in a Introduction, Detection, and Error Correction on Content using CRC algorithm.

Analysis of Capacity

Given the following polynomial that we have chosen to use in our CRC algorithm:

$G(x) = x^{7} + x^{5} + x^{4} + x^{3} + x^{1} + x^{0}$

(in binary: 0b10111001)

We can determine that the hamming distance of this polynomial is 4, which means that we can detect up to 3 errors and correct up to 1 error.

Overall Architecture

The established architecture is capable of handling multiple clients by connecting to a proxy, which is in turn connected to a server, using the TCP protocol with multi-threading support.

To send a message, the client inserts a character and then calculates its CRC (Cyclic Redundancy Check), which is concatenated to form a 2-byte packet:

+-----------+-----------+
| Message   | CRC       |
| (1 byte)  | (1 byte)  |
+-----------+-----------+

The client then sends the packet to the proxy, which modifies random bits in the first byte representing the message.

Note: We assume that the byte representing the CRC cannot be altered.

The proxy then forwards the modified packet to the server, which verifies its validity by performing a polynomial division in the binary field $F_2[X]$

Two cases can occur:

• If the remainder of the polynomial division is zero, there are no errors.
• If the remainder is non-zero, an error is detected and can be corrected by comparison with a software register.

If the server fails to correct the error, it sends a predefined value of 0xFFFF, indicating that the packet could not be corrected. The client then resends the packet until the server manages to correct the error.

Usage

In root directory:

make

you will need to execute in order:

Server

./bin/project-rio --server --server-address=localhost --server-port=9876

Proxy

./bin/project-rio --proxy --proxy-address=localhost --proxy-port=9800 --server-address=localhost--server-port=9876

Client

./bin/project-rio --client --proxy-address=localhost --proxy-port=9800

Note: You can use the --help flag to see the available options for each program.

Resources

• Ross N. Williams. : A painless guide to crc error detection algorithms
• Sunshine2K : Understanding and implementing CRC (Cyclic Redundancy Check) calculation

Authors

• Alexander Yanovskyy
• Roman Bonnet
• Jean-Raphäel Julien
• Romain Bourdain