Transmission Medium and physical layer

Is a types of communication medium in which communication

devices are directly linked with each other.

Media Issues

Frequency range

Some media support higher frequencies than others

Impairments

Different media deform signals differently

Some are more susceptible to noise and distortion

Cost

We’re in the real world

Number of receivers

Broadcast vs. point-to-point

Classes of transmission media

Guided media

Guided media, which are those that provide a pipe or passage

from one device to another, include twisted-pair cable, coaxial

cable, and fiber-optic cable

Twisted-Pair Cable Two copper conductors

Number of pairs are bundled together

More twists mean better quality (eliminate electromagnetic

interference effect)

least expensive, most widely used

limitation : data rate and distance (100 m)

Applications

Twisted-Pair Cable comes in two forms

Unshielded twisted pair cable (UTP)

UTP cable is the most common type of telecommunication

medium in use today

The range is suitable for transmitting both data and video.

Advantages of UTP are its cost and ease of use so it is flexible,

and easy to be installed.

Shielded twisted pair cable (STP)

has a metal foil that enhances each pair of insulated

conductors.

more expensive than UTP but less susceptible to noise

UTP connectors

UTP categories

Coaxial Cable

Coaxial cable is a copper-cored cable surrounded by a heavy

shielding. Outer conductor shields the inner conductor from

picking up stray signal from the air

Much better than twisted pair in attenuation

High bandwidth but lossy channel

Television distribution

Long distance telephone transmission

Traditional Ethernet LANs like 10Base2, or 10Base5.

Maximum cable length is 500 m

Coaxial Cable Standards

Coaxial Cable Connectors

Optical Fiber Cable

Is made of glass or plastic and transmits signals in the form

of light reflect through it.

It uses the principal of total internal reflection theorem

Fiber optic cable has the ability to transmit signals over much

longer distances than coaxial and twisted pair.

It also has the capability to carry information (higher

bandwidth) at vastly greater speeds (long-haul trunks). . This

capacity broadens communication possibilities to include

services such as video conferencing and interactive services.

The cost of fiber optic cabling is comparable to copper cabling

however.

It is difficult to be installed

Less signal attenuation

Propagation Modes

Current technology supports two modes for propagating light

along optical channel.

Fiber sizes

are defined by the ratio of the diameter of their core to the diameter

of their cladding.

Fiber-optic cable connectors

Unguided media, or wireless communication, transport

electromagnetic waves without using a physical conductor.

Instead the signals are broadcast though air, and thus are

available to anyone who has a device capable of receiving

them.

Susceptible to interference

Unguided media-Wireless

Radio Waves

Microwaves

IEEE 802.15 Infrared (Bluetooth)

(Institute of Electrical and Electronics Engineers)

Radio Waves

Electromagnetic waves ranging in frequencies between 3kHz

and 1Ghz.

Microwaves

are used for multicast communications, such as radio and

television, and paging systems

Infrared waves

use frequencies from 300 Ghz to 400 Thz, can be used for

short-range communication (1 to 100 m).