UNIT I
Overview of
Data Communications
and
Networking
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1.1 Data Communication
Components
Data Representation
Direction of Data Flow
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1-1 DATA COMMUNICATIONS
Where are the data communications?
Why data communications?
Telecommunication: communication at a distance.
Data: information presented in whatever form is agreed upon by the parties
creating and using the data.
Data communications: the exchange of data between two devices via some form
of transmission medium such as a wire cable.
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1-1 DATA COMMUNICATIONS
 What do we need?
Hardware
Software
 Four fundamental characteristics:
1.
2.
3.
4.
Delivery: correct destination
Accuracy: correct data
Timeliness: fast enough
Jitter: uneven delay
 Topics covered:
1. Components
2. Data representation
3. Data flow
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Figure 1.1
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Five components of data communication
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DATA REPRESENTATION
 Text
Email, articles, etc
Coding (Unicode, ASCII)
 Numbers
Direct conversion
 Images
Pixels, resolution, gray scale, RGB, YCM
 Audio
Continuous, signal conversion
 Video
Movie, continuous/discrete
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DIRECTION OF DATA FLOW
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Figure
1.2 Data flow (simplex, half-duplex, and full-duplex)
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Figure 1.13
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LAN
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Figure 1.13
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LAN (Continued)
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Figure 1.14
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MAN
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Figure 1.15
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WAN
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TYPES OF CONNECTION
POINT TO POINT
MULTIPOINT
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Figure 1.5
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Point-to-point connection
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Figure 1.6
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Multipoint connection
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Figure 1.7
Categories of topology
Topology
The way network is connected either physically or logically.
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Mesh
Example: telephone regional
offices
1
2
4
5
3
Advantages:
•
no traffic problems
•
Robust. No link failure no
effect on others.
•
Privacy security
•
Easy to detect the abnormal
situation.
Disadvantages:
•
Amount of cables, i/o ports
•
Efficiency and effectiveness
•
Space
•
Cost
Figure 1.5 A fully connected mesh topology (five devices)
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Figure 1.9
Star topology
Each node is connected to a device in the center of the network called
a hub.
The hub simply passes the signal arriving from any node to the other
nodes in the network.
The hub does not route the data.
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Star
Less expensive. One link
and I/o port
connecting to the
hub. No direct
traffic between two
devices.
Advantages:
•
Easy to install
•
Less cables
•
Maintain: add,
move, delete
•
Robustness
Figure 1.6 A star topology connecting four stations
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Disadvantages;
•
Hub is too
important
•
The hub represents
a single source of
failure
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Bus
•Each node is connected one after the other (like christmas lights)
•Nodes communicate with each other along the same path called the
backbone
Multipoint
Advantages:
•
Easy to install
•
Less cables
Disadvantages:
•
Hard to detect fault isolation.
•
Bus cable is too important
Figure 1.7 A bus topology connecting three stations
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Ring
•The ring network is like a bus network, but the “end” of the network
is connected to the first node
•Nodes in the network use tokens to communicate with each other
Point to point with 2 devices
on both sides
Figure 1.8 A ring topology connecting six stations
Advantages:
•
Easy to install
•
Maintain: add move
delete
•
Fault isolation
Disadvantages:
•
Unidirectional traffic
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Figure 1.10
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Bus topology
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Figure 1.8 A ring topology connecting six stations
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Figure 1.9 A hybrid topology: a star backbone with three bus networks
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1.4 Protocols and Standards
Protocols
Standards
Standards Organizations
Internet Standards
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Protocols and standard
 Protocols (rules)
1. Why do we need protocols?
2. Key elements of protocols
a) Syntax: structure or format of the data
b) Semantics: meaning of each section of bits
c) Timing: when sent and how fast
 Standards
1. De facto vs. De jure
2. Organizations
3. Internet standards (Internet draft & RFC)
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National Standards Organizations
(Generally responsible for standards within a nation and usually participate in that
nation’s international activity)
• American National Standards Institute (ANSI)
•International Standards Organizations
(Promote standards for worldwide use)
• International Standards Organization (ISO)
• International Telecommunications Union (ITU)consists of ITU-T, which is
responsible for communications, interfaces, and other standards related to
telecommunications.
• Electronic Industries Association (EIA)
• Institute for Electrical and Electronics Engineers (IEEE)
• Internet Engineering Task Force (IETF)
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