1. Unit III
Signals, Transmission & Performance
• Analog and Digital data,
• Analog and Digital signals,
• Digital Signals-Bit rate,
• Bit length
• Baseband Transmission,
• Broadband Transmission
• Transmission Impairments– Attenuation,
• Distortion and Noise Data Rate
• Limits– Noiseless channel: Nyquist’s bit rate,
• noisy channel : Shannon's law
• Performance of the Network Bandwidth,
• Throughput, Latency (Delay),
• Bandwidth –Delay Product, Jitters Line Coding Characteristics, Line Coding
Schemes– Unipolar -NRZ, Polar-NRZ-I, NRZ-L, RZ, Manchester and Differential
Manchester, Problems Transmission Modes, Parallel Transmission and Serial
Transmission– Asynchronous and Synchronous Multiplexing, FDM and TDM
Switching-Circuit Switching, Message Switching and Packet Switching.
2. Analog data
• Analog data is information represented by a continuously variable physical
quantity. It differs from digital data, which is represented by discrete, or non-
continuous, values. Analog data is characterized by its smooth, continuous
waveforms, and can take on any value within a given range.
Characteristics of Analog Data:
• Continuous:
• Analog data changes smoothly over time, representing a continuous range of
values.
• Examples:
• Natural phenomena like sound waves, voltage fluctuations, and radio waves are
examples of analog data.
• Measurement:
• Analog data can be thought of as a measurement or representation of something
that can fluctuate, like the intensity of a light or the temperature of a room.
3. Feature Analog Data Digital Data
Nature Continuous Discrete (binary)
Representation Waves Bits (0s and 1s)
Accuracy
High in natural
signals High in computing
Storage
Difficult without
noise
Easy and noise-
resistant
Devices
Thermometer, Tape
recorders
Computers,
CD/DVD players
4. Examples of Analog Data in Use:
• Audio: Microphones capture sound as analog
signals, which are then converted to digital for
storage or transmission in many modern systems.
• Temperature Sensors: Many temperature sensors
output an analog signal that varies with
temperature.
• Communication: Traditional telephone systems
and radio waves rely on analog signals.
5. Advantages and Disadvantages:
Advantages:
• Analog data can represent real-world phenomena with great
fidelity, as it captures the continuous nature of these phenomena.
Disadvantages:
• Analog signals can be susceptible to noise and degradation during
transmission. They may also require more complex circuitry for
processing.
• In summary, analog data is continuous and variable, reflecting the
natural world, while digital data is discrete and
quantized. Understanding the difference between the two is
fundamental in various fields, including electronics,
communication, and data processing.
6. Digital data
Digital data is information represented in a binary format (ones
and zeros) that a computer can understand and process. It's
the fundamental language of computers and is used to
represent everything from text and images to audio
Examples of Digital Data
• Text documents (e.g., Word files, emails)
• Images (e.g., JPEGs, PNGs)
• Audio recordings (e.g., MP3s, WAV files)
• Video files (e.g., MP4s, AVI files)
• Software code
• Spreadsheets (e.g., Excel files)
• audio and video.
8. Key Characteristics:
• Binary Representation:
• Digital data is fundamentally based on the binary system, using only two
states (0 and 1) to represent information.
• Discrete:
• Unlike analog data which is continuous, digital data is discrete, meaning it
has distinct, separate values.
• Machine-Readable:
• Digital data is structured in a way that computers can easily interpret and
manipulate.
• Versatile:
• Digital data can represent a wide range of information, including text,
numbers, images, audio, and video.
• No Physical Form:
• Digital data exists as electronic signals or patterns, not as physical objects.
9. Analog and digital signals
Analog and digital signals are two fundamental ways to
represent and transmit information. Analog signals are
continuous and can take on any value within a range, while
digital signals are discrete, meaning they have specific,
distinct values, often represented as binary (0s and 1s).
Analog signals are like a dimmer switch, continuously
adjusting, while digital signals are like a light switch, either
on or off. Digital signals have largely replaced analog
signals in modern technology due to their superior
robustness and efficiency.
11. Analog Signals:
• Continuous: They vary smoothly over time and can
represent a continuous range of values.
• Examples: Human voice, temperature readings,
voltage in a circuit, and sound waves.
• Characteristics: Can be represented by sine waves.
• Applications: Older technologies like record
players and tape recorders utilize analog signals.
• Disadvantages: Susceptible to noise and signal
degradation during transmission.
12. Digital Signals:
• Discrete: They have specific, distinct values, often
represented as binary code (0s and 1s).
• Examples: Data stored in a computer, digital clocks,
and digital audio files.
• Characteristics: Can be represented by square waves.
• Advantages: More resistant to noise and signal
degradation, can be easily regenerated, and are
efficient for data storage and transmission.
• Disadvantages: Can require more bandwidth than
analog signals for transmitting the same information.
14. Digital signals bit rate
• In digital signals, bit rate is the number of bits transmitted per second, and is a
measure of how quickly data is being transferred. It's a crucial factor in
determining the quality and speed of digital communication, often expressed in
bits per second (bps), kilobits per second (kbps), or megabits per second
(Mbps).
• Key points about bit rate:
• Definition:
• Bit rate represents the amount of data transferred per unit of time, specifically
bits per second.
• Measurement:
• It's commonly measured in bps (bits per second), kbps (kilobits per second),
Mbps (megabits per second), and Gbps (gigabits per second).
• Importance:
• Bit rate directly impacts the quality and speed of digital communication,
including audio and video streaming, file downloads, and other data transfers.
15. • Relationship to other terms:
• In digital signals, bit rate replaces frequency or period used for
analog signals.
• Bit rate vs. Baud rate:
• While both relate to data transmission speed, bit rate refers to the
number of bits transmitted, while baud rate (or signaling rate) refers
to the number of signal elements (symbols) transmitted per second.
• Example:
• A common audio format like MP3 uses bitrates between 128-320
kbps, with higher bitrates generally indicating better audio quality.
• Video streaming services like YouTube offer different quality options
(e.g., 144p, 720p, 1080p) based on varying bitrates, which
determine the video's clarity and smoothness.
16. Bit length
Bit length refers to the physical length that a single bit occupies on a transmission
medium. It is determined by the bit's duration (how long it lasts) and the
propagation speed of the signal on the medium. Essentially, it's the spatial
distance a bit covers as it travels from sender to receiver.
Bit Duration:
• This is the time it takes for a single bit to be transmitted. It's the inverse of the
bit rate (bits per second). For example, if the bit rate is 10 Mbps (10 million bits
per second), then the bit duration is 1/10,000,000 seconds.
• Propagation Speed:
• This is the speed at which the signal travels through the transmission medium
(e.g., copper wire, fiber optic cable, or wireless medium).
• Bit Length Calculation:
• Bit length is calculated by multiplying the propagation speed by the bit
duration.
• Formula: Bit Length = Propagation Speed * Bit Duration
17. • Example:
• If the propagation speed is 2 x 10^8 meters per second and the bit
duration is 0.1 microseconds (for a 10 Mbps signal), then the bit length is
20 meters.
• Significance:
• Understanding bit length is important for calculating signal propagation
delay and ensuring reliable data transmission, especially in high-speed
networks.
• In some network designs, like those using slotted ALOHA, the bit length
influences the slot time, which is the time it takes for a signal to traverse
the longest possible path in the network.
• Bit length is also relevant in understanding how different network
technologies and media affect signal characteristics and performance.
19. Baseband Transmission
• In baseband transmission, the data bits are
directly converted into signals. Generally a higher
voltage level represents the bit 1, while a lower
voltage level represents bit 0.
• The different encoding schemes are shown in the
diagram. Among these, the first three are come in
the category of polar encoding. In polar signaling,
one logical state is represented by only one
voltage state. In bipolar schemes, two voltage
levels may be used to represent a logical state.
20. NRZ (Non – Return to Zero)
NRZ is an unipolar coding scheme. Here, a high voltage represents 1, while a low
voltage represents 0. Non-return to zero implies that the signal does not return to
zero at the middle of the bit.
Manchester Encoding
Manchester encoding is a biphase coding scheme. Bit 1 is represented by a voltage
transition from high to low, while bit 0 is represented by a voltage transition from
low to high.
Bipolar Encoding
It is also called Alternate Mark Inversion or AMI. Three voltage levels are used here.
Here, bit 0 is represented by no line signal, while bit 1 is represented by a positive or
negative voltage level, alternating for successive ones.
22. • It is a transmission technology where a single signal is either sent or received
through a communication channel such as a cable, in the form of discrete pulses of
the single frequency.
• The frequency of the baseband signal is not altered. The signal bandwidth is almost
zero. As there is no frequency shifting in baseband systems, only one signal
occupies the entire bandwidth of the system at a time. Any remaining bandwidth is
therefore wasted.
• In this technology, multiple devices connected in a network communicate with each
other by transmitting and receiving data on a single communication channel, which
is shared among multiple devices using its entire bandwidth. Either transmission or
reception of data takes place at a time. The signal needs to be of one common type
which is ?understandable' by all the devices in the network. The same medium
however can be shared using Time Division Multiplexing (TDM).
• Ethernet-based wired Local Area Network (LAN) is a popular application of
baseband signal. The following image depicts transmission of Baseband signal ?
23. Advantages of Baseband Transmission
• Simple in implementation.
• Costs incurred for installation are low.
• Overall maintenance costs are lesser than
Broadband transmission costs.
Disadvantages of Baseband Transmission
• It can be used for transmission of only data
and voice.
• It works good only for short distance.
• Coverage of the signal is limited
24. It is a transmission technology where multiple signals of different frequencies are
simultaneously sent through a single communication channel.
At the transmitting end, entire bandwidth is logically divided into multiple signals using
a multiplexing device. These multiple signals are sent over the communication channel
such as Radio Waves or Optical Fiber. At the receiving end, the signals are accumulated
into one single signal using a demultiplexer device. Large files, audio, and video are
transmitted on broadband with high speed at long distances.
The following image depicts how broadband signal transmission takes place ?
Signals with different frequencies are taken by a Multiplexing device, transmitted
over the medium as one logical signal and then divided back to multiple signals.
Broadband Transmission
25. Types of Broadband Technologies
Six main types of broadband technologies are
• Digital Subscriber Line (DSL) ? In this type, the telephone wires are used
for accessing Internet. The DSL Modem is required to set-up the Internet
connection. The Internet Service Provider (ISP) sends the signal through
phone line to the DSL modem. The modem receives signal and converts it
to the signal you need to use the Internet.
• Cable Modem ? In this type, the cable television infrastructure is used to
access the Internet. It comprises of a modem inside user's place and a
coaxial wire or cable that runs from the modem to the Cable Modem
Termination System (CMTS) located in the premises of the ISP. Simply, it
works by connecting the modem to the CMTS using a coaxial cable.
• Optical Fiber ? In this type, fiber-optic cable is used for data transmission,
which can transmit data at a phenomenal speed of 70% the speed of light.
Fiber-optic cables are also tough on weather, and they reduce
maintenance costs.
26. • Wireless ? As the name depicts, there are no physical wired
involved for data traffic. Data is sent over radio waves. It requires
a wireless Internet modem, a wireless access card or Internet
dongle, and a Wireless Internet Connection Provider (WISP)
service. This technology is weather-dependent hence slower.
• Satellite ? A satellite dish is required to be installed on which the
data is projected from the space via the satellite orbiting around
the Earth. It provides wide reach ability even in the remote places
of the country.
• Broadband over Power Lines (BPL) ? In this technology of
transmission, overhead and underground power lines are used to
carry broadband data for long distances.
27. Advantages of Broadband Transmission
• Data transmission is fast.
• The transmission can take place for long
distances.
• Large bandwidth provision for transmission.
Disadvantages of Broadband Transmission
• Additional hardware such as Multiplexers and
De-multiplexers are required.
• High cost of implementation and maintenance is
high.
29. Transmission Impairments
• Transmission impairment occurs when the received signal is different
from the transmitted signal. As we know, a signal can be transmitted
as Analog signal or it can be transmitted as a digital signal.
• In Analog signals due to transmission impairment the resulting
received signal gets different amplitude or the shape. In the case of
digitally transmitted signals at the receiver side we get changes in bits
(0's or 1's).
Causes of Transmission Impairments
• There are various causes of transmission impairments
• Noise
• Distortion
• Attenuation
30. Noise
• Noise is the major factor for the transmission
distortion as any unwanted signal gets added to the
transmitted signal by which the resulting transmitted
signal gets modified and at the receiver side it is
difficult to remove the unwanted noise signal. These
noises are various kinds like shot noise, impulse
noise, thermal noise etc.
• Noise is diagrammatically represented as follows
31. Distortion
• This kind of distortion is mainly appearing in case of composite signals in which a
composite signal has various frequency components in it and each frequency
component has some time constraint which makes a complete signal.
• But while transmitting this composite signal, if a certain delay happens between
the frequencies components, then there may be the chance that the frequency
component will reach the receiver end with a different delay constraint from its
original which leads to the change in shape of the signal. The delay happens due to
environmental parameters or from the distance between transmitter and receiver
etc.
• Distortion is diagrammatically represented as follows
32. Attenuation
• Attenuation is generally decreased in signal strength, by
which the received signal will be difficult to receive at
the receiver end. This attenuation happens due to the
majority factor by environment as environment imposes
a lot of resistance and the signal strength decreases as it
tries to overcome the resistance imposed.
