Chapter 1 The Big Picture Introduction to Computer Networks and Data Communications

Data Communications & Computer Networks, Second Edition

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Chapter 1

The Big Picture

Introduction to Computer Networks and Data Communications


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Who today has not used a computer network?

Examples?

Introduction


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The Language of Computer Networks Computer network

Local area network

Metropolitan area network


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The Language of Computer Networks Wide area network

Personal area network

Data communications


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The Language of Computer Networks Voice network

Data network

Telecommunications

Network management


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The Big Picture of Networks

Networks are composed of many devices, including: workstations (computers and telephones) network servers network hubs and switches (bridges) routers (LAN-WAN and WAN-WAN) telephone switching gear


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Computer Networks - Basic Configurations Computer terminal-to-mainframe computer Microcomputer-to-mainframe computer Microcomputer-to-local area network Microcomputer-to-Internet Local area network-to-local area network Local area network-to-metropolitan area network Personal area network-to-workstation Local area network-to-wide area network Sensor-to-local area network Satellite and microwave Wireless telephone and wired telephone-to-network


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Computer terminal to mainframe computer

Predominant form in 60s and 70s. Still used in many types of businesses for

data entry and data retrieval. Usually involves a low-speed connection.


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Microcomputer-to-Local Area Network

Highly common throughout business and academic environments, and now even homes

Typically a medium- to high-speed connection Microcomputer requires a NIC (network interface

card) NIC connects to a hub-like device


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Microcomputer-to-Internet

Very popular with home users and some small businesses

Typically a dial-up modem is used to connect user’s microcomputer to an Internet service provider.

Newer technologies such as DSL (digital subscriber line) and cable modems are replacing dial-up modems.


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Local Area Network-to-Local Area Network

Found in businesses and schools that have two or more LANs and a need for them to intercommunicate.

A bridge-like device is typically used to interconnect LANs.

Bridge-like device can filter traffic


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Personal Area Network-to-Workstation Interconnects devices such as PDAs,

laptops, and music playback devices using wired or wireless transmission

Used over a short distance such as a few meters


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Local Area Network-to-Metropolitan Area Network Used to interconnect companies (usually

local area networks) to networks that encompass a metropolitan city

High speed networks with redundant circuits


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Local Area Network-to-Wide Area Network One of the most common ways to

interconnect a user on a LAN workstation to the Internet (a wide area network).

A router is the typical device that performs LAN to WAN connections.

Routers are more complex devices than bridges/switches


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Sensor-to-Local Area Network

Not all local area networks deal with microcomputer workstations.

Often found in industrial and laboratory environments.

Assembly lines and robotic controls depend heavily on sensor-based local area networks.


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Satellite and Microwave Long distance wireless connections. Many types of applications including long

distance telephone, television, radio, long-haul data transfers, and wireless data services.

Typically expensive services but many companies offer competitive services and rates.


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Network Architecture Models A reference model that describes the layers of

hardware and software necessary to transmit data between two points.

Reference models are necessary to increase the likelihood that different components from different manufacturers will converge.

There are two models that are required learning: The OSI Model, and the Internet Model.


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OSI Model

Seven layers


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OSI Seven Layers Application layer

where the application using the network resides. Common network applications include remote login, file transfer, e-mail, and web page browsing.

Presentation layer performs a series of miscellaneous functions necessary for

presenting the data package properly to the sender or receiver.

Session layer responsible for establishing sessions between users.

Transport layer provides an end-to-end error-free network connection. Makes sure

the data arrives at the destination exactly as it left the source.


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OSI Seven Layers Network layer

responsible for creating, maintaining and ending network connections. Transfers a data packet from node to node within the network

Data link layer responsible for taking the data and transforming it into a frame with

header, control and address information, and error detection code. Physical layer

handles the transmission of bits over a communications channel. Includes voltage levels, connectors, media choice, modulation techniques.


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The Internet Model (TCP/IP Model)


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OSI Model vs. Internet Model Application layer - equivalent to the OSI’s

presentation and application layers Transport layer - performs same function as OSI

transport layer Network layer - roughly equivalent to the OSI’s

network layer Interface layer - equivalent to the OSI’s physical

and data link layers


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Logical and physical connections Logical and physical

connections.

Note that in a network architecture model, only the lowest layer contains a physical connection, while all higher layers contain logical connections


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Network Models in Action


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The Internet Model in Action See Figure 1-19 on pp. 25 Note the flow of data from user to web browser

and back At each layer, information is either added or

removed, depending on whether the data is leaving or arriving at a workstation

Adding information over pre-existing information is termed encapsulation


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Chapter 1 The Big Picture Introduction to Computer Networks and Data Communications

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