Noise in Networking

Noise in Networking

Networking involves one sender and one receiver. The sender sends signals to the receiver via a transmission medium for example, wire. Unfortunately, the transmission mediums are not perfect, so the signal received is not what is sent. One of the reasons for the transmission impairment is noise.

Noise in Networking
Fig 1: Noise in Networking

In networking, noise is an unwanted signal produced in the transmission medium. It comes from the sources that carry electricity - for example, AC power cables, motors, and fluorescent lights. It affects the quality of the desired signal.

The noise can be:

  1. Thermal Noise
  2. Induced Noise
  3. Crosstalk
  4. Impulse Noise

Thermal Noise

The thermal noise is generated due to the random motion of electrons in a wire. Thermal noise is always present in the electrical equipment and is directly proportional to the temperature of the wires. It is also known as Johnson-Nyquist noise, Johnson noise, or Nyquist noise. Elimination of thermal noise is impossible; however, reducing the temperature or resistance in electrical circuits can reduce the thermal noise.

Induced Noise

Induced noise is the noise that produced in a circuit by a fluctuating magnetic or electrostatic field produced by another circuit. For example, AC power cables produce magnetic fields, and fluorescent light produces electrostatic fields. Once this electrostatic or magnetic energy gets in the equipment, the energy is converted to noise, called induced noise. The induced noise can be reduced by using twisted pair cables, proper grounding, and shielding the networking cables.


In crosstalk, the signal in one wire affects the signal in the other wire. One wire act as sending antenna, and the other wire acts as receiving antenna. Crosstalk could cause you can hear someone else's discussion. Twisted-pair cable, shielded cable, and keeping cables further apart help avert crosstalk.

Impulse Noise

Impulse noise is a spike generated in the transmission medium from power lines or lightning. Impulse noise increases or decreases a circuit's signal level; this causes the receiving equipment to misinterpret the signal.

A noise-free medium is not possible in reality. So, the signal delivered to the receiver always has a noise component, and therefore, a significant noise power. The ratio of the average signal power to the average noise power is called signal-to-noise ratio or SNR. High SNR means the signal is less corrupted by noise, and low SNR means the signal is more corrupted by the noise. Therefore, a larger SNR makes it easier for the receiver to extract the transmitted signal from the background noise.

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