mcgraw-hill©the mcgraw-hill companies, inc., 2004 overview of data communications and networking...
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McGraw-Hill © The McGraw-Hill Companies, Inc., 2004
Overview of Data Communications
and Networking
UNIT I
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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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What do we need?
HardwareSoftware
Four fundamental characteristics:
1. Delivery: correct destination2. Accuracy: correct data3. Timeliness: fast enough4. Jitter: uneven delay
Topics covered:
1. Components2. Data representation3. Data flow
1-1 DATA COMMUNICATIONS
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Figure 1.1 Five components of data communication
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DATA REPRESENTATION
Text
Email, articles, etcCoding (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 1.13 LAN
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Figure 1.13 LAN (Continued)
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Figure 1.14 MAN
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Figure 1.15 WAN
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TYPES OF CONNECTION
POINT TO POINT
MULTIPOINT
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Figure 1.5 Point-to-point connection
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Figure 1.6 Multipoint connection
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Figure 1.7 Categories of topology
The way network is connected either physically or logically.
Topology
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Mesh
Figure 1.5 A fully connected mesh topology (five devices)
1
2
3
4
5
Example: telephone regional offices
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
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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
Figure 1.6 A star topology connecting four stations
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
Disadvantages;• Hub is too
important• The hub represents
a single source of failure
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Bus
Figure 1.7 A bus topology connecting three stations
Multipoint
Advantages:• Easy to install• Less cables
Disadvantages:• Hard to detect fault isolation.• Bus cable is too important
• Each node is connected one after the other (like christmas lights)• Nodes communicate with each other along the same path called the
backbone
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Ring
Figure 1.8 A ring topology connecting six stations
Point to point with 2 devices on both sides
Advantages:• Easy to install• Maintain: add move
delete• Fault isolation
Disadvantages:• Unidirectional traffic
• 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
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Figure 1.10 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 (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 jure2. Organizations3. Internet standards (Internet draft & RFC)
Protocols and standard
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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)