MyNoteBook : Transmission Media

Transmission Media is a pathway that carries the data information from transmitter to receiver. There are different types of waves or cables to transmit data. Information is transmitted normally through electrical (Current) or electromagnetic signals (at different frequencies). These signals can be transmitted through different Medias like copper wires, atmosphere, water, and optical fibre. Different media have different properties like bandwidth, ease of installation, cost and delay. Characteristic and quality are determined by signal and medium. For guided transmission, medium is important. For unguided transmission, bandwidth is important. Key concerns in transmission are data rate and distance.

Types of Transmission Media

Transmission media is divided into two groups:

1. Guided or Wired or Bounded Transmission Media

2. Unguided or Wireless or Unbounded Transmission Media

Figure: Transmission medium and physical layer

There are various design factors:
1. Bandwidth: Higher bandwidth gives higher data rate
2. Interference
3. Transmission Impairments
4. Number of Receivers: More receivers introduce more attenuation, need more amplifiers and repeaters.

Guided or Wired Media are the cables that have physical existence and are limited by environmental geography. Mostly used wired media are co-axial cable, twisted pair cable, and optical cable. Each media has its own properties like speed of transmission, effect of noise, cost etc.

Unguided or Wireless Media are the way of transmitting information without using any physical media or cables. It is also known as wireless communication. Example, wireless LAN are used in office and college campuses. This transmission uses radio wave, microwave, infrared waves.

Table: Transmission Characteristics of Guided Media

	Frequency Range	Typical Attenuation	Typical Delay	Repeater Spacing
Twisted Pair	0 to 3.5 KHz	0.2 dB/km	50 µs/km	2 km
Coaxial Cable	0 to 500 MHz	7 dB/km	4 µs/km	1 to 9 km
Optical fiber	186 to 370 Thz	0.2 to 0.5 dB/km	5 µs/km	40 km