Coding Schemes in Computer Networks

In computer networks, coding schemes are used to convert digital data into signals that can be transmitted over a communication channel. These coding schemes serve various purposes, including error detection, synchronization, and efficient transmission of data. They are crucial in ensuring that data sent over networks is transmitted accurately and efficiently.

Let’s discuss some common coding schemes used in computer networks.

1. Line Coding

Line coding is the process of converting digital data into a digital signal. It is a method to represent binary data (1s and 0s) using signal levels over a transmission medium.

Types of Line Coding:

Unipolar Encoding
- In unipolar encoding, all the data is represented by positive voltages (for 1) or zero voltages (for 0). A 0 is represented by 0 volts, and a 1 is represented by a positive voltage.Example:
  - 0 → 0 volts1 → +5 volts
  Advantages: Simple and easy to implement.Disadvantages: It has a DC component, which makes it less efficient for long-distance transmission.
Example: : 1 0 1 1 Signal: +5V 0V +5V +5V
Polar Encoding
- In polar encoding, the binary digits are represented by two voltage levels: positive voltage for 1 and negative voltage for 0, or vice versa.Example:
  - 0 → -5 volts1 → +5 volts
  Advantages: Provides better signal strength as compared to unipolar encoding.
Example: 1 0 1 1 Signal: +5V -5V +5V +5V
Manchester Encoding
- In Manchester encoding, each bit is represented by two signal levels, which help with synchronization. A ‘1’ is represented by a transition from high to low, and a ‘0’ is represented by a transition from low to high within one clock cycle.Advantages: Self-synchronizing and suitable for reliable data transmission.
Example: 1 0 1 1 Signal: high → low, low → high, high → low, high → low
Differential Manchester Encoding
- In this encoding scheme, a transition occurs at the beginning of each bit interval for a ‘1’, while no transition occurs at the beginning of the bit interval for a ‘0’.
- Advantages: Provides better synchronization, even in noisy environments.

2. Block Coding

Block coding involves grouping data bits into blocks and then encoding them into longer codewords. This encoding ensures that the encoded data adheres to specific properties, such as error detection.

Example: 4B/5B Encoding

4B/5B encoding is used to map 4-bit data into 5-bit codewords. This extra bit helps in ensuring a balanced number of 1s and 0s, which makes transmission more reliable.Example:
- Data: 1101 (4 bits)
- Codeword: 11110 (5 bits)

Benefits:

Block coding helps with error detection and synchronization, making it more robust in noisy environments.

3. Huffman Coding

Huffman coding is a type of lossless data compression used for efficient data transmission. It works by assigning variable-length codes to input characters, with shorter codes for more frequent characters and longer codes for less frequent ones. This scheme is particularly useful when the data includes repetitive patterns.

Example:

Suppose you need to encode the following characters with frequencies:
- ‘A’ = 5, ‘B’ = 9, ‘C’ = 12, ‘D’ = 13, ‘E’ = 16, ‘F’ = 45
The characters will be encoded using the shortest possible code lengths, where the most frequent characters get shorter codes.Huffman Tree:scssCopyEdit F(45) / \ D(13) E(16) / \