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Data Communications. Chapter 1 – Data Communications, Data Networks, and the Internet. Eighth Edition by William Stallings. Data Communications, Data Networks, and the Internet.

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Data Communications

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Data Communications

Chapter 1 – Data Communications, Data Networks, and the Internet

Eighth Edition

by William Stallings

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Data Communications, Data Networks, and the Internet

  • The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point - The Mathematical Theory of Communication, Claude Shannon

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Contemporary Data Comms

  • Trends influenced by:

    • traffic growth at a high & steady rate

    • Requirement / development of new services

    • advances in technology

  • significant change in requirements led to:

    • emergence of high-speed LANs

    • corporate WAN needs

    • Use of digital electronics

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A Communications Model

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Key Communications Tasks

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Data Communications Model

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Transmission Medium

  • selection is a basic choice

    • internal use entirely up to business

    • long-distance links made by carrier

  • rapid technology advances affects choice

    • fiber optic – high capacity, getting cheaper

    • Wireless - mobility

  • transmission cost is still high

  • hence interest in efficiency improvements – multiplexing and compression

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  • growth of number & power of computers is driving need for interconnection

  • also seeing rapid integration of voice, data, image & video technologies

  • two broad categories of communications networks:

    • Local Area Network (LAN)

    • Wide Area Network (WAN)

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Wide Area Networks

  • span a large geographical area

  • rely in part on common carrier circuits

  • alternative WAN technologies used include:

    • circuit switching

    • packet switching

    • frame relay

    • Asynchronous Transfer Mode (ATM)

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Circuit Switching

  • uses a dedicated communications path established for duration of communication

  • comprising a sequence of physical links

  • with a dedicated logical channel

  • eg. telephone network

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Packet Switching

  • data sent out in sequence

  • small chunks (packets) of data at a time

  • packets passed from node to node between source and destination

  • used for terminal to computer and computer to computer communications

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Frame Relay

  • packet switching systems have large overheads to compensate for errors

  • modern systems are more reliable

  • errors can be caught in end system

  • Frame Relay provides higher speeds

  • with most error control overhead removed

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Asynchronous Transfer Mode

  • ATM - evolution of frame relay

  • fixed packet (called cell) length

  • with little overhead for error control

  • anything from 10Mbps to Gbps

  • constant data rate using packet switching technique with multiple virtual circuits

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Local Area Networks

  • smaller scope

    • Building or small campus

  • usually owned by same organization as the attached devices

  • data rates much higher within

  • switched LANs, eg Ethernet

  • wireless LANs

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Metropolitan Area Networks

  • MAN

  • middle ground between LAN and WAN

  • private or public network

  • high speed

  • large area – city or metro

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Types of connections: point-to-point and multipoint

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Categories of topology

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A fully connected mesh topology (five devices)

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A star topology connecting four stations

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A bus topology connecting three stations

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A ring topology connecting six stations

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A hybrid topology: a star backbone with three bus networks

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  • # In a network with 25 computers, which topology would require the least extensive cabling?

    • Mesh

    • Star

    • Bus

    • Ring

    • # For six devices connected in mesh, how many cables are needed? How many ports are needed for each device?

    • # What is the consequence if a connection fails for five devices arranged in:

    • a) Mesh b) Star (excluding hub) c) Bus d) Ring

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The Internet

  • Internet evolved from ARPANET

    • first operational packet network

    • applied to tactical radio & satellite nets also

    • had a need for interoperability

    • led to standardized TCP/IP protocols

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Internet Elements

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Internet Architecture

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Example Configuration

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The protocol/medium/signal/all the above is the physical path over which message travels.

The information to be communicated in a data communications system is the medium/protocol/message/transmission.

Frequency of failure and network recovery time after a failure are measures of the performance/reliability/security/feasibility of a network.

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  • introduced data communications needs

  • communications model

  • defined data communications

  • overview of networks

  • introduce Internet

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