Introduction to Computer Networks and Data Communications

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Data Communications and Computer Networks

The Language of Computer Networks

• Computer network - an interconnection of computers and computing equipment using either wires or radio waves over small or large geographic distances • Local area network - networks that are small in geographic size spanning a room, building, or campus • Metropolitan area network - networks that serve an area of 3 to 30 miles - approximately the area of a typical city 1 2

Data Communications and Computer Networks

The Language of Computer Networks

• Wide area network - a large network that encompasses parts of states, multiple states, countries, and the world •Personal area network – a network of a few meters, between wireless devices such as PDAs, laptops, and similar devices.

•Voice network - a network that transmits telephone signals •Data network - a network that transmits computer data 1 3

Data Communications and Computer Networks

The Language of Computer Networks

• Data communications - the transfer of digital or analog data using digital or analog signals •Telecommunications - the study of telephones and the systems that transmit telephone signals •Network management - the design, installation, and support of a network and its hardware and software 1 4

Data Communications and Computer Networks

The Big Picture of Networks

• Networks are composed of many devices, including: • workstations (computers and telephones) • servers • network hubs and switches (bridges) • routers (LAN-WAN and WAN-WAN) • telephone switching gear 1 5

Data Communications and Computer Networks

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Data Communications and Computer Networks

Network Architectures

• A reference model that describes the layers of hardware and software necessary to transmit data between two points or for multiple devices / applications to interoperate • Reference models are necessary to increase the likelihood that different components from different manufacturers will converse • There are two architectures that are required learning: The OSI Model, and the TCP/IP protocol suite 1 7

Data Communications and Computer Networks

Network Architectures

• The OSI Model’s seven layers 1 8

Data Communications and Computer Networks

Network Architectures

•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 1 9

Data Communications and Computer Networks

Network Architectures

• 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.

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

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Data Communications and Computer Networks

Network Architectures

• 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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Data Communications and Computer Networks

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Data Communications and Computer Networks

Network Architectures

• The TCP/IP protocol suite 1 13

Data Communications and Computer Networks

Network Architectures

• Application layer - equivalent to the OSI’s presentation and application layers •Transport layer - performs same function as OSI transport layer •Network (Internet or internetwork) layer - roughly equivalent to the OSI’s network layer •Network access (data link/physical) layer - equivalent to the OSI’s physical and data link layers 1 14

Data Communications and Computer Networks

Network Architectures

• Logical and physical connections - A logical connection is one that exists only in the software, while a physical connection is one that exists in the hardware.

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

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Data Communications and Computer Networks

Network Architectures

• Logical and physical connections 1 16

Data Communications and Computer Networks

Network Architectures

• Example of data flow through layers 1 17

Data Communications and Computer Networks

Network Connections in Action

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Data Communications and Computer Networks

The TCP/IP Protocol Suite in Action

• 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 • The adding of information over pre-existing information is termed

encapsulation

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Data Communications and Computer Networks Chapter 1

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Data Communications and Computer Networks

Review Questions

• A user is sitting at work using a laptop computer with a wireless connection into the corporate LAN. The user is sending email. What basic connections are being used?

• List the seven OSI layers with a quick description of each layer.

• List the TCP/IP layers with a quick description of each layer.

•What is the difference between a logical and a physical interface / connection?

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