Presentation of value in terms of wave or discrete form is calledsignal basically we have two types of signal. Analog are generalwave based signal. And digital signal are discrete (0&1)basedsignal in data communication some time we have to convert thesignal from analog to digital and some time digital to analog

Signal

Frequency

The frequency of a periodic function is the number ofcomplete cycle that can occur per second. Frequency isdenoted with lower case ‘f’. Frequency has unite of Herz orcycle per second.

Amplitude

The amplitude of the given wave is the value if the wave ofthat point. Amplitude is also known as the magnitudes ofthe wave at that point. There are no particular variable thatis used with amplitude, although capital A, capital M,capital R are common

Bandwidth

The amount of data that can be carried from one point toanother in a given period of time (usually in second). Thiskinds of bandwidth is usually expressed in bit of data persecond(bps).

Analog and digital transmission

There are tow types of transmission signal popular in the devices. Some devicesuse digital signal directly and some need the conversion of signal to use. Wehave to perform the digital signal due to following reasons.

1. Capacity utilization is high on digital signal.2. It is easy to maintain privacy on digital processing.3. It is the modern technology which uses discrete

signal to processing digital data.4. It enhance the existing digital equipment.

Transmission impairments

Disturbance due to the communication media andvariation of signal and their frequency are calledimpairments. There are three basic type of impairments .They are given below.

Attenuation

Distortion

Noise

Attenuation

1. Increase the strength of thesignal and frequency to transferthe signal .

2. Use the amplifier to orrepeaters to again and restoreit's original strength of thesignal

It is a phenomena where the strength of the signal is reduce and finally falls off with some distances. We have to use some technique to reduce the attenuation these are give below.

Distortion

Impairment due to the variation of the velocities of a signal is calleddistortion. Due to this impairment the signal may varies so that recipient mapis not able to get the complete from of the signal such delay phenomena tocalled delay distortion.

We can minimize such impairmentsby selection the suitablecommunication media specially thewired transmission media.

Noise

Receptor will receive the signal with some unwanted signal mixed with the original signal is called noise . Such noise are mixed with the message signal form various sources these are

A. Thermal B. Intermodulation C. Cross talk D. impulse

Synchronous and Asynchronous transmission

Synchronous

Transmission of data by making sameblock and transfer in the form ofstream of block is called synchronoustransmission.

Asynchronous

Transmission of the signal with thecharacter by character or frame byframe is called asynchronoustransmission it can transfer the signalwith low frequency speed channeland the variation of the signalstrength of channels,