Data Communication Network
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Transcript of Data Communication Network
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Data Communication Network
331: STUDY DATA COMMUNICATIONS AND NETWORKS
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331: STUDY DATA COMMUNICATIONS AND NETWORKS
1. Discuss computer networks (5 hrs) 2. Discuss data communications (15 hrs)
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331.2: Discuss Data Communications PERFORMANCE STANDARD
◦ Given a network system, identify and illustrate the different data communications components clearly
Objectives:◦ Define elements of a communication system◦ Define data communications◦ Discuss various types of transmission media and
their characteristics◦ Discuss encoding of information for transmission◦ Discuss types of signal & their characteristics◦ Relate data capacity of a channel and bandwidth◦ Classify media based on bandwidth◦ Discuss channel organization
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SKILL AREA 331.2.3
Discuss encoding of information for transmission
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Data vs. Information
Data raw facts no context just numbers and
text
Information data with context processed data value-added to data
◦ summarized◦ organized◦ analyzed
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We have all seen computers do seemingly miraculous things with all kinds of sounds, pictures, graphics, numbers, and text.
All of the wonderful multi-media that we see on modern computers is all constructed from simple ON/OFF switches - millions of them - but really nothing much more complicated than a switch.
The trick is to take all of the real-world sound, picture, number etc data that we want in the computer and convert it into the kind of data that can be represented in switches.
Data in computer
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Data in computer
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Data Encoding
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Data Encoding refers the various techniques of impressing data (0,1) or information on an electrical, electromagnetic or optical signal that would propagate through the physical medium making up the communication link between the two devices.
Data Encoding
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Digital Data, Analog Signals [modem] Digital Data, Digital Signals [wired LAN] Analog Data, Digital Signals [codec]
◦ Frequency Division Multiplexing (FDM)◦ Wave Division Multiplexing (WDM) [fiber]◦ Time Division Multiplexing (TDM)◦ Pulse Code Modulation (PCM) [T1]◦ Delta Modulation
Data Encoding Techniques
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Two types of data Analog and Digital Two types of Signals (transmission
techniques) Analog and Digital
Data and Signals
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The signal is exact Signals can be checked for errors Noise/interference are easily filtered out A variety of services can be offered over
one line Higher bandwidth is possible with data
compression
Advantages of Digital Transmission
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Advantages of Analog Transmission Most mediums support analog transmission
- used for wireless communication The telephone infrastructure provides a
relatively cheap “individual point-to-point” transmission
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Interpreting Signals Need to know
◦ Timing of bits - when they start and end◦ Signal levels
Factors affecting successful interpreting of signals◦ Signal to noise ratio◦ Data rate◦ Bandwidth
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Comparison of Encoding Schemes (1) Signal Spectrum
◦ Lack of high frequencies reduces required bandwidth
◦ Lack of dc component allows ac coupling via transformer, providing isolation
◦ Concentrate power in the middle of the bandwidth Clocking
◦ Synchronizing transmitter and receiver◦ External clock◦ Sync mechanism based on signal
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Comparison of Encoding Schemes (2) Error detection
◦ Can be built in to signal encoding Signal interference and noise immunity
◦ Some codes are better than others Cost and complexity
◦ Higher signal rate (& thus data rate) lead to higher costs
◦ Some codes require signal rate greater than data rate
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Analog Signals Carrying Analog and Digital Data
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Digital Signals Carrying Analog and Digital Data
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Digital Data - Digital Signal It is logical to represent digital data with a
digital signal Digital signal
◦ Discrete, discontinuous voltage pulses◦ Each pulse is a signal element◦ Binary data encoded into signal elements
Signal changes value as the data changes value from 0 to 1 and 1 to 0
Several line encoding schemes are possible. Each has pros and cons
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Encoding Schemes There are many encoding schemes. We will
focus on:◦ Nonreturn to Zero-Level (NRZ-L)◦ Nonreturn to Zero Inverted (NRZI)◦ Manchester◦ Differential Manchester
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Nonreturn to Zero-Level (NRZ-L) Two different voltages for 0 and 1 bits Voltage constant during bit interval
◦ no transition I.e. no return to zero voltage e.g. Absence of voltage for zero, constant
positive voltage for one More often, negative voltage for one value
and positive for the other This is NRZ-L
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Nonreturn to Zero Inverted Nonreturn to zero inverted on ones Constant voltage pulse for duration of bit Data encoded as presence or absence of
signal transition at beginning of bit time Transition (low to high or high to low)
denotes a binary 1 No transition denotes binary 0 An example of differential encoding
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NRZ
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NRZ pros and cons Pros
◦ Easy to engineer◦ Make good use of bandwidth
Cons◦ dc component◦ Lack of synchronization capability
Used for magnetic recording Not often used for signal transmission
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Ensures that each bit has some type of signal change
Solves the synchronization problem. There is always a transition in the middle of
the interval. Manchester code signal:
◦ Changes from high to low in the middle of the interval to transmit a 0, and
◦ Changes from low to high in the middle of the interval.
Manchester Digital Encoding Schemes
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Used in most local area networks No transmission in the beginning interval = 1 Transmission in the beginning interval = 0 Receiver can synchronize itself with the
incoming bit stream. Disadvantage: Nearly half of the time there
will be two transitions during each bit. Hardware has to work twice as hard of that of NRZ encode signal.
Therefore it can be inefficient.
Differential Manchester
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Manchester Encoding
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Differential Manchester Encoding
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Examples of four digital encoding schemes
Digital Data - Digital Signal
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Analog Data, Digital Signal Digitization
◦ Conversion of analog data into digital data◦ Digital data can then be transmitted using NRZ-L◦ Digital data can then be transmitted using code
other than NRZ-L◦ Digital data can then be converted to analog
signal◦ Analog to digital conversion done using a codec◦ Pulse code modulation◦ Delta modulation
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Digitizing Analog Data
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Analog Data, Digital Signal Digitization
◦ Conversion of analog data into digital data◦ Digital data can then be transmitted using NRZ-L◦ Digital data can then be transmitted using code
other than NRZ-L◦ Digital data can then be converted to analog
signal◦ Analog to digital conversion done using a codec◦ Pulse code modulation◦ Delta modulation
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Digitizing Analog Data
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Pulse Code Modulation(PCM) (1) If a signal is sampled at regular intervals at
a rate higher than twice the highest signal frequency, the samples contain all the information of the original signal.
Voice data limited to below 4000Hz Require 8000 sample per second Analog samples (Pulse Amplitude
Modulation, PAM) Each sample assigned digital value
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Pulse Code Modulation(PCM) (2) 4 bit system gives 16 levels Quantized
◦ Quantizing error or noise◦ Approximations mean it is impossible to recover
original exactly 8 bit sample gives 256 levels Quality comparable with analog
transmission 8000 samples per second of 8 bits each
gives 64kbps
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Analog Data, Analog Signals Why modulate analog signals?
◦ Higher frequency can give more efficient transmission
◦ Permits frequency division multiplexing Types of modulation
◦ Amplitude◦ Frequency◦ Phase
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Analog Modulation
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QUESTION?