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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)