TRANSMISSION MEDIUM

Dept. of electronics and communication

Presented by:-

Content

• Transmission media• Types of transmission media• Guided media - Twisted pair cable - Coaxial cable - Fiber optic cable• Unguided media - Radio wave - Microwave - Infrared

Transmission media

• Transmission media are located below the physical layer.

• Signals are transmitted in the form of electromagnetic energy.

Types of transmission media

Guided media

• The transmission capacity depend on the medium , the length and whether the medium is point to point or multipoint.

• for example:- local area network (LAN).• For guided media the medium is more

important in determining the limitation of transmission.

Guided media-twisted pair cable

TWISTED-PAIR CABLE

Twisted-pair

• One of the wires carries signal, the other is used only as a ground reference.

• The receiver uses the difference b/w the two levels.

• Twisting increases the probability that both wires are effected by the noise in the same manner, thus the difference at the receiver remains same.

• Therefore, number of twists per unit length determines the quality of the cable

Types of twisted-pair

• Unshielded twisted pair (UTP)• Shielded twisted pair (STP)

Unshielded twisted pair (UTP)

• Ordinary telephone wire• Cheapest• Easiest to install• Suffers from external EM interference

Shielded twisted pair (STP)

• Metal braid or Sheathing that reduces interference• More expensive• Harder to handle (thick and heavy)

Guided media-UTP connector

Twisted Pair - Applications

• Most common medium• Telephone network• Within buildings• For local area networks (LAN)

Guided Media - Coaxial Cable

Coaxial cable

• Inner conductor is a solid wire outer conductor serves both as a shield against noise and a second conductor

APPLICATION• Most versatile medium• Television distribution• Long distance telephone transmission• Can carry 10,000 voice calls simultaneously

Guided Media - Coaxial Cable

• BNC CONNECTOR-(Bayonet-Neill-concealman)

Guided Media - Fiber-Optic Cable

OPTIC FIBER CABLE

Optical Fiber - Transmission Characteristics

• uses total internal reflection to transmit light• can use several different light sources– Light Emitting Diode (LED)• cheaper, wider operating temp range,

lasts longer– Laser Diode •more efficient, has greater data rate,

narrow range.

Guided Media – Fiber-Optic Cable

• Propagation mode

Guided Media – Fiber-Optic cable

Propagation modes

Guided Media – Fiber-Optic Cable

Fiber-optic cable connector

Applications of Fiber Optics

• Backbone networks due to wide bandwidth and cost effectiveness

• Up to 1600 Gbps with WDM • Cable TV• LANS

Advantage of fiber optics

• Higher bandwidth than twisted-pair and coaxial cable; not limited by medium, but by equipment used to generate and receive signals.

• Noise resistance• Less signal attenuation • Immunity to EMI • Lightweight• Greater security

Disadvantage of fiber optics

• Installation and maintenance• Unidirectional light propagation -for bidirectional communication two fibers are needed.• cost - cable and interfaces are relatively more expensive than other guided media

Unguided Media

• Electromagnetic spectrum for wireless communication

Wireless propagation method

• Ground – radio waves travel through lowest portion of atmosphere, hugging the Earth.

• Sky – higher-frequency radio waves radiate upward into ionosphere and then reflect back to Earth.

• Line-of-sight – high-frequency signals transmitted in straight lines directly from antenna to antenna.

Unguided Media

• Propagation method

Unguided media

• Wireless transmission wave

Unguided media

• It provided a means for transmitting electromagnetic signal but do not guided for example:-wireless communication.

• In other words we can say that for unguided media the bandwidth of the signal produced by the transmitting antenna and the size of antenna is more important than the medium.

Unguided media-radio wave

Omnidirectional antenna

• Frequencies between 3 KHz and 1KHZ

• used for multicasts communications, such as radio and television, and paging system.

Radio wave

• Frequency ranges: 3 KHz to 1 GHz• Omni directional • Susceptible to interference by other antennas

using same frequency or band• Ideal for long-distance broadcasting• May penetrate walls• Apps: AM and FM radio, TV, maritime radio,

cordless phones, paging

Unguided Media – Microwaves

• Frequency between 1 to 300 GHZ.• Used for unicast communication such as cellular phones,

satellite networks and wireless LANs.

Microwave

• Frequencies between 1 and 300 GHz• Unidirectional• Narrow focus requires sending and receiving

antennas to be aligned • Issues: – Line-of-sight (curvature of the earth; obstacles)– Cannot penetrate walls

Microwave application

• Unicasting – one-to-one communication between sender and receiver– Cellular phones– Satellite networks– Wireless LANs

Unguided media-Infrared

Frequencies between 300 GHz to 400 THz.

Can not penetrate walls.

Used for short-range communication in a closed area using line-of-sight propagation

Infrared

• modulate non-coherent infrared light• end line of sight (or reflection)• are blocked by walls• no licenses required• typical uses– TV remote control– IRD port

Infrared application

• Wide bandwidth available for data transmission.

• Communication between keyboards, mice, PCs, and printers.

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