This document discusses key concepts in data communication including transmitters, receivers, transmission mediums, analog and digital signals, modulation, error correction, and bandwidth. It covers transmission modes like simplex, half-duplex, and full-duplex. Impairments during transmission like attenuation, noise, and delay are also summarized. Digital transmission uses repeaters to regenerate signals over long distances while avoiding noise amplification.

1. Data Communication
Data
Transmission
Introduction of some concepts & terms
used.
• Transmitter
• Receiver
• Medium

2. 2
—Com. in form of electromagnetic waves
—Guided medium
• Along a physical path
• e.g. twisted pair, optical fiber
—Unguided medium
• Means for transmitting electromagnetic waves but
not guide them
• e.g. air, water, vacuum

3. 3
• Direct link
—No intermediate devices
—Transmission path between 2 devices
—Can apply to both guided & unguided media
• Point-to-point
—Direct link
—Only 2 devices share link
• Multi-point
—More than two devices share the link

4. 4
Transmission mode :
• Simplex
—One direction
• e.g. Television
• Half duplex
—Either direction, but only one way at a time
• e.g. police radio
• Full duplex
—Both directions at the same time
• e.g. telephone

5. 5
• Data
—Entities that convey meaning or info
• Signals
—Electric or electromagnetic representations of
data
• Transmission
—Communication of data by propagation and
processing of signals

6. Analog and Digital Data
6
• Analog
—Continuous values within some interval
—e.g. sound, video
• Digital
—Discrete values
—e.g. text, integers

7. Da
Co
ta and Computer
mmunications 8
Analogue & Digital Signals

8. Data and Computer
Communications 9
Periodic
Signals
Amplitude
Period = T = 1/f
Period = T = 1/f
Amplitude

9. 10
Sine Wave
Fundamental periodic signal
• Peak Amplitude (A)
—maximum strength of signal
—volts
• Frequency (f)
—Rate of change of signal
—Hertz (Hz) or cycles per second
—Period = time for one repetition (T)
—T = 1/f
• Phase (
—Relative position in time

10. Components of Speech
10
• Frequency range (of hearing) 20Hz-20kHz
—Speech 100Hz-7kHz
• Easily converted into electromagnetic signal for
transmission
• Sound frequencies with varying volume
converted into electromagnetic frequencies with
varying voltage
• Limit frequency range for voice channel
—300-3400Hz

11. Conversion of Voice Input into
Analog Signal
11

12. Binary Digital Data
• Generated by computer terminals etc.
—Converted into digital voltage pulses for
transmission
• Two dc components
—Voltage levels – 1s and 0s
• Bandwidth of signal depends on data rate
—Bandwidth approximation of digital pulse
stream
12

13. Conversion of PC Input to
Digital Signal
-
-
1 signal = 0.02 msec
1 sec = 1000 msec = 50,000 bits
13

14. Data and Signals
• Usually use digital signals for digital data and
analog signals for analog data
• Can use analog signal to carry digital data
—Modem (modulator/demodulator)
Digital
signal
modulator
Analog
signal
demodulator
Digital
signal
14
Transmission
medium

15. Data and Signals(2)
• Usually use digital signals for digital data and
analog signals for analog data
• Can use digital signal to carry analog data
—Compact Disc audio
—Codec (coder-decoder)
Analog
signal
digital
signal
15
codec receiver
Transmission
medium
A codecencodes a data stream or a signal for transmission and storage, possibly in
encrypted form, and the decoder function reverses the encoding for playback or
editing.

16. Data and Computer
Communications 18
Analog Signals Carrying Analog
and Digital Data

17. Data and Computer
Communications 19
Digital Signals Carrying Analog
and Digital Data

18. A transceiver means a unit which contains both a receiver
and a transmitter.
Historically, transceiver was used to interface computers to peripherals such as
modems, printers, keyboards, joysticks, and a mouse
Today, transceiver is used in applications such as GPS, POS, glucose meters,
barcode scanners, automotive telemetric, set-top boxes, gaming, and many
others that require low-cost, low-speed
Transceivers can handle analog or digital signals, and in some cases, both.
The transceivers will still be used in applications where lower cost and
design simplicity are important.
In future applications lower supply voltages and higher data rates will be
considered for newer designs. Future integration will likely include
galvanic isolation and overvoltage protection.

19. Bandwidth
Bandwidth is also defined as the amount of data that can be transmitted in a fixed
amount of time. For digital devices, the bandwidth is usually expressed in bits per
second(bps) or bytes per second. For analog devices, the bandwidth is expressed in
cycles per second, or Hertz (Hz).
Bandwidth is also described as the carrying capacity of a channel or the data
transfer speed of that channel. ...
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20. Analog Transmission
• Analog signal transmitted without regard to content
• May be analog or digital data
— Eg: Analog data: voice,
Digital data: binary data that passed through a
modem
• Attenuated over distance
• Use amplifiers to boost signal
• Also amplifies noise
• Disadvantage: distance distortion
— Analog data (eg. voice) :distortion can be tolerated
— Digital data :introduce errors
Attenuation is a general
term that refers to any
reduction in the
strength of a signal.
Attenuation occurs with
any type of signal,
whether digital or
analog. Sometimes
called loss,
attenuation is a natural
consequence of signal
transmission over long
distances

21. An amplifier is an electronic device that increases the voltage,
current, or power of a signal.
Amplifiers are used in wireless communications and
broadcasting, and in audio equipment of all kinds.
They can be categorized as either weak-signalamplifiers or
power amplifiers.
An audio power amplifier (or power amp) is an electronic
amplifier that reproduces low-power electronic audio
signals such as the signal from radio receiver or electric
guitar pickup at a level that is strong enough for driving
(or powering) loudspeakers or headphones.

22. Digital Transmission
22
• Concerned with content(binary)
• Integrity endangered by noise, attenuation etc.
-limited distance
• Repeaters used
— Repeater receives digital signal
— Extracts bit pattern
• recover the patterns of 1s and 0s
— Retransmits
• a new signal
• Attenuation is overcome
• Noise is not amplified

23. RepeatersIn telecommunications, a repeater is an electronic device that receives a signal and
retransmits it.Repeaters are used to extend transmissions so that the signal can cover longer
distances or be received on the other side of an obstruction.
A repeater is a network device that is used to regenerate or replicate signals that are
weakened or distorted by transmission over long distances and through areas with high
levels of electromagnetic interference (EMI).

24. Advantages of Digital
Transmission
Data and Computer
Communications 24
• Digital technology
— Low cost LSI/VLSI technology
• Data integrity
— Longer distances over lower quality lines
• with the use of repeater(regenerate) rather than amplifier
• Capacity utilization
— High bandwidth links economical.
• eg: satellite channels, optical fiber
— High degree of multiplexing easier with digital techniques
• Time division multiplexing (TDM) rather than frequency division multiplexing
(FDM)
• Security & Privacy
— Encryption
• To digital data and analog data that have been digitized
• Integration
— Can treat analog and digital data similarly

25. LSI/VLSI
Very-large-scale integration (VLSI) is the process of creating
an integrated circuit (IC) by combining hundreds of thousands
of transistors or devices into a single chip.
VLSI began in the 1970s when
complex semiconductor and communication technologies were
being developed. T
he microprocessor is a VLSI device.
Before the introduction of VLSI technology most ICs had a limited
set of functions they could perform. An electronic circuit might
consist of a CPU, ROM, RAM and other glue logic.
VLSI lets IC designers add all of these into one chip.

26. Data and Computer
Communications 43
•
•
•
•
The first integrated circuits contained only a few transistors. Called "Small-
Scale Integration" (SSI), they used circuits containing transistors numbering
in the tens.
The next step in the development of integrated circuits, taken in the late 1960s,
introduced devices which contained hundreds of transistors on each chip, called
"Medium-Scale Integration" (MSI).
They were attractive economically because while they cost little more to
produce than SSI devices, they allowed more complex systems to be produced
using smaller circuit boards, less assembly work (because of fewer separate
components), and a number of other advantages.
Further development, driven by the same economic factors, led to "Large-
Scale Integration" (LSI) in the mid 1970s, with tens of thousands of
transistors per chip.
Integrated circuits such as 1K-bit RAMs, calculator chips, and the first
microprocessors, that began to be manufactured in moderate quantities in the
early 1970s, had under 4000 transistors. True LSI circuits, approaching 10,000
transistors, began to be produced around 1974, for computer main memories
and second-generation microprocessors.
The final step in the development process, starting in the 1980s and continuing
on, was "Very Large-Scale Integration" (VLSI), with hundreds of thousands
of transistors, and beyond (well past several million in the latest stages).
For the first time it became possible to fabricate a CPU on a single integrated
circuit, to create a microprocessor.
LSI and VLSI

28. Transmission Impairments
28
• Signal received may differ from signal
transmitted
• Analog - degradation of signal quality
• Digital - bit errors
• Caused by
—Attenuation and attenuation distortion
—Delay distortion
—Noise

29. Attenuation
Data and Computer
Communications 29
• Signal strength falls off with distance
• Depends on medium
• Received signal strength:
—must be enough to be detected
—must be sufficiently higher than noise to be received
without error
—Can be deal by using amplifier/repeater
• Attenuation is an increasing function of frequency
—Noticeable for analog signal
—Use equalizer to smooth out attenuation effect
—Use amplifier to amplify high freq. more than low freq.

30. Noise (1)
• Additional signals inserted between transmitter
and receiver
1. Thermal
—Due to thermal agitation of electrons
—Uniformly distributed
—White noise, cannot be eliminated
2. Intermodulation
—Signals that are the sum and
difference of original frequencies
sharing a medium
Intermodulation
Data and Computer
Communications 30

31. Noise (2)
3. Crosstalk
—A signal from one line is picked up by another
4. Impulse
—Irregular pulses or spikes
• e.g. External electromagnetic interference
—Short duration
—High amplitude
—Sharp spike could change a 1 to 0 or
Data and Computer
Communications a 0 to 1. 31

32. Data and Computer
Communications 44
FDM and TDM
FDM
TDM
TDM (Time Division Multiplexing) and FDM (Frequency Division Multiplexing) are two
methods of multiplexing multiple signals into a single carrier. Multiplexing is the process
of combining multiple signals into one, in such a manner that each individual signal can
be retrieved at the destination

33. 40
CONCLUSION
• Successful transmission of data depends
principally on 2 factors
— Quality of the signal being transmitted
— Characters of the transmission medium
Data and Computer
Communications

34. 41
Key Points
• All forms of info. can be represented by
electromagnetic signals
• Analog or Digital signals can be used to
convey info.
• The greater the bandwidth of the signal, the
greater its info.-carrying capacity
Data and Computer
Communications

35. 42
Key Points (2)
• Major problem in designing a com. facility is
transmission impairment
—Attenuation, delay attenuation, noise (thermal
noise, intermodulation noise, crosstalk, impulse
noise)
• Designer of com. facility must deal with 4
factors
—Bandwidth of signal, data rate that is used for
digital info., amount of noise & other impairments,
and the level of error rate that is acceptable.
Data and Computer
Communications