DC Lec 11 (Signals)

8/3/2019 DC Lec 11 (Signals)

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DATA

COMMUNICATION


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The OSI Model

Functions of OSI Layers

TCP/IP Protocol Suite


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Signals

Analog and Digital

Analog and Digital Data & Signals

Periodic & Aperiodic Signals


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Generally, the information is not in a form that canbe transmitted over a Link

The binary digits must be converted into a form thatTransmission Medium can accept

The data stream of 1s and 0's must be turned intoSignals


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Signaling is the way data is transmitted across themedium.

The data/information to be communicated is transmittedin such a way that it can be understood by the receiver,

and this is done byencoding (in terms of digital signaling)

modulation (in terms of analog signaling).

The information to be communicated can exist in both forms, i.e.analog and digital.

The two signaling methods correspond to the two types of datadescribed are: Digital Signaling and

Analog Signaling.


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ANALOG

Refers to something that is Continuous.

An analog signal has infinitely many levels of intensity over a

period of time. CONTINUOUS

A set of specific points of data and all possible points betweenthem.

A digital signal has only a limited number of defined values,often as simple as 1 and 0.


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DIGITAL

Refers to something that is Discrete.

DISCRETE

A set of specific points of data with no points in between.


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For example,

An analog clock that has hour, minute, and second hands

gives information in a continuous form; the movements ofthe hands are continuous.

On the other hand, a digital clock that reports the hoursand the minutes will change suddenly from 8:05 to 8:06.


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Periodic

Signals(Analog or Digital)

Aperiodic


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A signal is called Periodic if it completes apattern within a measurable time frame called

a Period and then repeats that pattern overidentical subsequent Periods


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An Aperiodic or Non-Periodic signal is the onethat changes constantly without exhibiting a

pattern or cycle that repeats over time


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Sine waves can be fully described:

Amplitude Period / Frequency

Phase


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The peak amplitude of a signal is the absolute value

of its highest intensity, proportional to the energy itcarries. For electric signals, peak amplitude is

normally measured in volts.ExampleThe power in your house can be represented by a sine

wave with a peak amplitude of 155 to 170 V.

However, it is common knowledge that the voltage of thepower in U.S. homes is 110 to 120 V.


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Period refers to the amount of time, in seconds, a

signal needs to complete 1 cycle.

Frequency refers to the number of periods in I s.

Note:Period and frequency are just one characteristic defined in

two ways. Period is the inverse of frequency, andfrequency is the inverse of period, as the following

formulas show.T= 1 / f OR f=1 / T


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Seconds____Hertz

Milliseconds____KilohertzMicroseconds____Megahertz

Nanoseconds____Gigahertz

Picoseconds____Terahertz


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Signals

Analog and Digital

Analog and Digital Data & Signals

Periodic & Aperiodic Signals

Sine Waves and its Characteristics


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Section

3.1,

3.2 Data Communications and Networking 4th Edition by

Behrouz A. Forouzan

DC Lec 11 (Signals)

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