04-signals carried over the network1

8/9/2019 04-Signals Carried Over the Network1

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Signals Carried over the


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Types of Information and Their RequirementsThis information that is transmitted through the networkma be an one of the followin :

Speech (telephony, fixed, or cellular); Moving images (television or video); Printed pages or still picture (facsimile or multimedia

messaging); Music; All types of computer information such as program

.


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Communication Requirements of Different Applications


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Analog and Digital Signals


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Analog and Digital Signals

A special and very important case of digital signalsis a binary signal where only two values, binary

Binary signals are used internally in computers andother digital systems to represent any digital signal.,

the slope in Figure 3.4 into three binary bits and

each of these three bit words then represents one of= .another example, a digital signal with eight-bit wordsor bytes (often called octets in digital

= 256 discrete values of a signal. These kinds ofdigital numbers are used to represent analog voice,in which each sam le of a voice si nal is encodedinto eight-bit words,


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Advantages of Digital Technology

The most important advantages of digital technologyover analog technology are as follows: g a unc ons ma e a g sca e o n egra on poss e. Digital technology results in lower cost, better reliability,

less floor s ace, and lower ower consum tion. Digital technology makes communication quality

independent of distance. . Digital networks are ideal for growing data

communication.

g a ec no ogy ma es new serv ces ava a e. Digital system provides high transmission capacity. Digital networks offer flexibility.


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Analog Signals over Digital Networks

Digital networks provide communication only with a setof discrete symbols (in the binary case these symbolsare ca e s a a cer a n a a ra e an e ana ogsignal has to be converted into a series of these symbolsfor digital communication.

The data rate of a digital network corresponds to the

channel bandwidth of an analog network. The higher the,versa.

If the network is fully digital, analog voice is encoded intodigital form at the transmitting end and decoded intoanalog form at the receiving end


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Analog Signals over Digital NetworksThis process has two main phases:

1. Analog-to-digital conversion (A/D): An analog signal is

values are then represented as numerical values by theencoder. These values, presented as binary words, aret en transm tte w t n regu ar t me per o s t roug t edigital channel.

2. Di ital-to-analo conversion D/A : At the other end ofthe channel, the decoder receives numerical values of thesamples that indicate the values of the analog signal at

.amplitudes corresponding to the values of the originalsignal at sampling instants are reconstructed and theser es ey orm s ere o pro uce an ana og s gna

close to the original one.


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Analog Signals over Digital Networks


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Pulse Code Modulation (PCM

PCM is a standardized method that is used in the telephone networkto change an analog signal to a digital one for

network. The analog signal is first sampled at a 8-kHz sampling

rate; then each sample is quantized into 1 of 256 levelsand the encoded into digital eight-bit words.

8,000 8 = 64 Kbps.

In the United States one bit of eight in every sixth frame

is robbed for in-band signaling and the availabletransparent data capacity of a single speech channel inthe network is reduced to 8 000 7 = 56 Kb s.


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Pulse Code Modulation (PCMow we a e a more e a e oo a e ree ma n

processing phases of the PCM in the telecommunicationsnetwork.


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Pulse Code Modulation (PCM) - Sampling

sampling frequency or sampling rate, and it depends onthe highest frequency component present in the analogsignal.

The relation of sampling frequency and the highest

follows:If the sampling frequency, fs , is higher than two times the

g es requency componen o e ana og s gna , , eoriginal analog signal is completely described by theseinstantaneous samples alone; that is, fs > 2 W.

This minimum sampling frequency is sometimes calledthe Nyquist rate .


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Pulse Code Modulation (PCM) - Quantizing


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Pulse Code Modulation (PCM) - Encoder

04-signals carried over the network1

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