Kenya Coconut Production Presentation by Dr. Lalith Perera
DCCN S1.ppt
1. PAN African e-Network Project
MFC
Data Communication and Computer Network
Semester – IV
Session - 1
By – Sapna Sinha
2. Agenda
• Introduction to Data Communication
• Data Flow
• Transmission Mode
• Signals
• Transmission Impairments
• Networks and Its type
• Topology
• Protocols
• Modulation
• Sampling
3. Data Communications
• Data
– Raw facts about any thing is known as data.
• Data communication
– Exchange of data between two devices
– Via some form of transmission medium
• Fundamental characteristics of data communication
– Delivery
– Accuracy
– Timeliness
– Availability
4. Five Components of Data
Communication
• Message: Information (data) to be communicated
• Sender
• Receiver
• Transmission medium: Physical path by which a message
travels
• Protocol: A set of rules that govern data communication
7. Transmission Medium
• Medium
– Guided medium
• e.g. twisted pair, optical fiber
– Unguided medium
• e.g. air, water, vacuum
8. Terminology
• Direct link
– No intermediate devices
• Point-to-point
– Direct link
– Only 2 devices share link
• Multi-point
– More than two devices share the link
10. Data Flow
• Simplex
– Unidirectional
– As on a one-way street, Television
• Half-duplex
– Both transmit and receive possible, but not at the same time
– Like a one-lane road with two-directional traffic
– Walkie-talkie, CB radio
• Full-duplex
– Transmit and receive simultaneously
– Like a two-way street, telephone network
– Channel capacity must be divided between two directions
11. Frequency, Spectrum and
Bandwidth
• Time domain concepts
– Continuous signal
• Various in a smooth way over time
– Discrete signal
• Maintains a constant level then changes to another
constant level
– Periodic signal
• Pattern repeated over time
– Aperiodic signal
• Pattern not repeated over time
15. Parallel Transmission
• Use n wires to send n bits at one time synchronously
• Advantage: speed
• Disadvantage: cost Limited to short distances
16. Serial Transmission
• One communication channel
• Advantage: reduced cost
• Parallel/serial converter is required
• Three ways: asynchronous, synchronous, or
isochronous
17. Asynchronous Transmission
• Use start bit (0) and stop bits (1s)
• A gap between two bytes: idle state or stop bits
• It means asynchronous at byte level
• Good for low-speed communications (terminal)
18. Synchronous Transmission
• Bit stream is combined into “frames”
• Special sequence of 1/0 between frames: No gap
• Timing is important. It use clock signal.
• Communication device is synchronized with internal
clock
• Advantage: speed high-speed transmission
19. Analog and Digital Data
Transmission
• Data
– Entities that convey meaning
• Signals
– Electric or electromagnetic representations of
data
• Transmission
– Communication of data by propagation and
processing of signals
20. Analog and Digital Signals
• To be transmitted, data must be transformed to
electromagnetic signals
• Data can be analog or digital.
• Analog data are continuous and take
continuous values. e.g. sound, video
• Digital data have discrete states and take on
discrete values. text, integers
21. Signals
• Means by which data are propagated
• Analog
– Continuously variable
– Various media
• wire, fiber optic, space
– Speech bandwidth 100Hz to 7kHz
– Telephone bandwidth 300Hz to 3400Hz
– Video bandwidth 4MHz
• Digital
– Use two DC components
25. Analog Transmission
• Analog signal transmitted without regard to
content
• May be analog or digital data
• Attenuated over distance
• Use amplifiers to boost signal
• Also amplifies noise
26. Digital Transmission
• Concerned with content
• Integrity endangered by noise, attenuation etc.
• Repeaters used
• Repeater receives signal
• Extracts bit pattern
• Retransmits
• Attenuation is overcome
• Noise is not amplified
27. Advantages of Digital Transmission
• Digital technology
– Low cost LSI/VLSI technology
• Data integrity
– Longer distances over lower quality lines
• Capacity utilization
– High bandwidth links economical
– High degree of multiplexing easier with digital
techniques
• Security & Privacy
– Encryption
• Integration
– Can treat analog and digital data similarly
28. Periodic Analog Signals
• Periodic analog signals can be classified as simple or composite.
• A simple periodic analog signal, a sine wave, cannot be decomposed
into simpler signals.
• A composite periodic analog signal is composed of multiple sine waves
• Sine wave is described by
– Amplitude
– Period (frequency)
– phase
33. Wavelength
• Another characteristic of a signal traveling through a
transmission medium
• Binds the period or the frequency of a simple sine wave to the
propagation speed of the medium
• Wavelength = propagation speed x period
= propagation speed/frequency
34. Composite Signals
• A single-frequency sine wave is not useful in
data communications; we need to send a
composite signal, a signal made of many simple
sine waves
• According to Fourier analysis, any composite
signal is a combination of simple sine waves
with different frequencies, phases, and
amplitudes
35. Bandwidth
• The bandwidth of a composite signal is the difference between
the highest and the lowest frequencies contained in that signal
37. Bit Rate and Bit Interval
Bit Rate: No. of bits transmitted per unit time.
38. Example
• Assume we need to download text documents at the rate of 100
pages per minute. What is the required bit rate of the channel?
Solution
• A page is an average of 24 lines with 80 characters in each line.
If we assume that one character requires 8 bits, the bit rate is
39. Transmission of Digital Signals
• Baseband transmission: Sending a digital signal
without changing into an analog signal
40. Broadband Transmission (Using Modulation)
• In Broadband Transmission , we need to
convert the digital signal to an analog signal
before transmission.
42. Transmission Impairments
• Signal received may differ from signal
transmitted
• Analog - degradation of signal quality
• Digital - bit errors
• Caused by
– Attenuation and attenuation distortion
– Delay distortion
– Noise
44. Attenuation
• Reduction in the strength of signal during transmission.
• Loss of energy to overcome the resistance of the
medium: heat
45. Distortion
• The signal changes its form or shape
• Each signal component in a composite signal has its own
propagation speed
• Differences in delay may cause a difference in phase
46. Noise
• Corruption of signals due to inferences.
• Additional signals inserted between transmitter and receiver
47. Noise
• Thermal
– Due to thermal agitation of electrons
• Intermodulation
– Signals that are the sum and difference of original
frequencies sharing a medium
• Crosstalk
– A signal from one line is picked up by another
• Impulse
– Irregular pulses or spikes
– e.g. External electromagnetic interference
– Short duration
– High amplitude
48. Performance
• Bandwidth
– Bandwidth in bits per second, refers to the speed
of bit transmission in a channel or link.
• Throughput
– Measurement of how fast we can actually send
data through a network
• Latency (Delay)
– Define how long it takes for an entire message to
completely arrive at the destination from the time
the first bit is sent out from the source
49. Data Rate & Signal Rate
• Data rate defines the number of data elements (bits) sent in 1s:
bps
• Signal rate is the number of signal elements sent in 1s: baud
50. Network
• Network: A set of devices (nodes) connected by communication
links
• Node: Computer, printer, or any device capable of sending
and/or receiving data
• To be considered effective and efficient, a network must meet a
number of criteria
51. Basic Components of Computer
Network
• Sending Device
• Receiving Device
• Hardware Components
– NIC, Repeaters, Hub, Switches, Routers,
Bridges, Gateways etc.
• Software Components
– Protocols, NOS
53. Type of Connection
• Point-to-point
– Dedicated link between two devices
– The entire capacity of the channel is reserved
– Ex) TV remote control
• Multipoint
– More than two devices share a single link
– Capacity of the channel is either
• Spatially shared: Devices can use the link simultaneously
• Timeshare: Users take turns
55. Hardware Components
• NIC (Network Interface Card)
– Used to connect computer on network
– Provide an interface to media
• Repeaters
– It connects two segment of network cable
– It retimes & regenerates the signals to proper
amplitudes and send them to other segments
56. Hardware Components Contd..
• Hub
– It is Central connecting device in computer network
– It is a box, used to gather groups of PCs together at
central location
– It receive information on one port & distribute to all
other active ports
57. Hardware Components Contd..
• Switch
– It is hardware device that joins multiple
computer together within one LAN
– Its intelligent than Hub, by determining source
& destination device of each packet
58. Hardware Components Contd..
• Routers
– More sophisticated network devices than switch/hub
– Box has
• Connection point for multiple computers
• Connection for electric power
• No. of LED lights to display device status
– It join LAN & WAN
– In large network it acts as intermediate destination for
traffic
59. Hardware Components Contd..
• Bridges
– It read outermost section of data on data
packet to tell where messages are going
– It reduces the traffic on outer network
segments
• Gateways
– A gateway can translate information between
different network data
60. Circuit Switching
• Dedicated communications path
established for the duration of the
conversation
• e.g. telephone network
61. Packet Switching
• Data sent out of sequence
• Small chunks (packets) of data at a time
• Packets passed from node to node
between source and destination
• Used for terminal to computer and
computer to computer communications
62. Frame Relay
• Packet switching systems have large
overheads to compensate for errors
• Modern systems are more reliable
• Errors can be caught in end system
• Most overhead for error control is stripped
out
63. Asynchronous Transfer Mode
• ATM
• Evolution of frame relay
• Little overhead for error control
• Fixed packet (called cell) length
• Anything from 10Mbps to Gbps
• Constant data rate using packet switching
technique
65. Mesh Topology
• Dedicated point-to-point link
to every other nodes
• A mesh network with n
nodes has n(n-1)/2 links. A
node has n-1 I/O ports (links)
• Advantages: No traffic
problems, robust, security,
easy fault identification &
isolation
• Disadvantages: Difficult
installation/reconfiguration,
space, cost
66. Star Topology
• Dedicated point-to-point link only to a central controller, called a
hub
• Hub acts as an exchange: No direct traffic between devices
• Advantages: Less expensive, robust
• Disadvantages: dependency of the whole on one single point,
the hub
67. Bus Topology
• One long cable that links all nodes
• tap, drop line, cable end
• limit on the # of devices, distance between nodes
• Advantages: Easy installation, cheap
• Disadvantages: Difficult reconfiguration, no fault isolation, a fault
or break in the bus stops all transmission
68. Ring Topology
• Dedicated point-to-point link only with the two
nodes on each sides
• One direction, repeater
• Advantages: Easy reconfiguration, fault
isolation
• Disadvantage: Unidirectional traffic, a break in
the ring cab disable the entire network
69. Hybrid Topology
• Example: Main star topology with each branch
connecting several stations in a bus topology
• To share the advantages from various topologies
70. Protocols
• Protocol : rule
– A set of rules that govern data communication
– Used for communications between entities in a system
– For communication to occur, entities must agree upon
a protocol
• Entities
– User applications
– e-mail facilities
– terminals
• Systems
– Computer
– Terminal
– Remote sensor
71. Key elements of a protocol
– Syntax: structure or format of data
– Semantics: meaning of each section in the
structure
• error handling
– Timing: when and how fast data should be
sent
• Speed matching
• Sequencing
74. Pulse Code Modulation
• PCM (Pulse Code Modulation)
• Three processes
– The analog signal is sampled
– The sampled signal is quantized
– The quantized values are encoded as streams of
bits
76. Pulse amplitude Modulation
• PAM (Pulse amplitude Modulation)
– According to the Nyquist theorem, the
sampling rate must be at least 2 times the
highest frequency contained in the signal.
