Introduction to Networking

Line Coding

Line Coding is an encoding technique that is used to convert digital data into digital signals. This process is done at the physical layer of the OSI Model because the OSI model is used in digital communication to transmit data from source to destination.

Important Terms 

  • Data Element: A data element is the smallest piece of information that we want to send, i.e., bit 0 or 1.
  • Signal Element: It is a shortest element of signal.
  • Data Rate: Data elements are sent in one second. It is measured in bit/sec
  • Signal Rate/Baud rate: Signal elements are sent in one second. SI unit is baud.

Important: Our basic need in encoding to transfer maximum bits (data element) per signal element. So, according to different encoding techniques (Explained below), one or more than one bit can be transferred in one signal element. Sometimes, more than one signal element is required to transmit one bit.

According to Manchester’s encoding, the following figure explains all the above factors.

Reasons for Line Coding

To resolve the following factors, we use the line coding

I. Bandwidth Problem

High bandwidth will be required when one digital bit is transferred through more than one element of the signal.

  • For bit 0, half of the signal is represented by -V and half by zero voltage.
  • for bit 1 half of the signal is represented by +V and half by zero voltage
  • Example: Data = 01001.

II. DC Problem

  • Due to series of same bit values, a constant rate is generated. It is called the DC component, which is difficult to handle as in the following diagram continuous of 1. So to Eliminate the DC factor Line coding is used.

III. Synchronization Problem

When a digital signal represents its beginning, mid, and end for each digital bit, then there will be no synchronization problem. in the following diagram, there is no synchronization problem

However, in the following cases, there will be a problem with process synchronization because the midpoints of each signal element are not defined.