William Stallings Data and Computer Communications 7th Edition

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William StallingsData and Computer
Communications7th Edition

• Chapter 1Data Communications and Networks
  Overview

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A Communications Model

• Source
• generates data to be transmitted
• Transmitter
• Converts data into transmittable signals
• Transmission System
• Carries data
• Receiver
• Converts received signal into data
• Destination
• Takes incoming data

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Simplified Communications Model - Diagram
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Simplified Data Communications Model
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Networking

• Point to point communication not usually
  practical
• Devices are too far apart
• Large set of devices would need impractical
  number of connections
• Solution is a communications network
• Wide Area Network (WAN)
• Local Area Network (LAN)

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Wide Area Networks (WAN)

• Large geographical area
• Consists of intermediate nodes
• provides switching from node to node
• Rely in part on common carrier circuits
• Implementation
• Traditionally
• Circuit switching
• Packet switching
• Recently
• Frame relay
• Asynchronous Transfer Mode (ATM)

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Circuit Switching

• Dedicated communications path established for the
  duration of the conversation
• Connection oriented communication
• Establish a circuit
• Transmit messages
• Release the circuit
• Example ?Telephone Network

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Packet Switching

• Data sent out of 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
• Most overhead for error control is stripped out
• Frame is a variable size of data
• Intermediate node does not perform error
  detection correction

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Asynchronous Transfer Mode (ATM)

• ATM is also known as cell relay network
• Fixed packet size, called Cells
• Gives almost same overhead for error control
• It gives less processing overhead than the frame
  relay
• Higher layer performs error detection
  correction
• Anything from 10Mbps to Gbps
• Constant data rate using packet switching
  technique

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Local Area Networks (LAN)

• Smaller scope than WAN
• Building or small campus
• Usually owned by a single organization
• E.g., CS and ECE have their own LANs
• Data rates much higher than WAN
• LAN Configuration
• Switched LANs
• Switched Ethernet LAN
• May consists of one or more switches
• Wireless LANs
• Allow user mobility
• Ease of installation

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Metropolitan Area Networks (MAN)

• A MAN is optimized for a larger geographical area
  than a LAN
• Unlike LAN, it ranges from several blocks of
  buildings to entire cities
• Like LAN, a MAN might be owned and operated by a
  single organization
• Often provide means for internetworking of local
  networks (for example UB entire campus network)
• Gives High speed and covers Large area

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Further Reading

• Read Chapter 1
• Web site for Stallings book
• http//williamstallings.com/DCC7e.html