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William Stallings Data and Computer Communications 7 th Edition

William Stallings Data and Computer Communications 7 th Edition. Chapter 1 Data Communications and Networks Overview. A Communications Model . Source generates data to be transmitted Transmitter Converts data into transmittable signals Transmission System Carries data Receiver

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William Stallings Data and Computer Communications 7 th Edition

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  1. William StallingsData and Computer Communications7th Edition Chapter 1Data Communications and Networks Overview

  2. 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

  3. Simplified Communications Model - Diagram

  4. Simplified Data Communications Model

  5. 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)

  6. 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)

  7. 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

  8. 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

  9. 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

  10. 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 givesless processing overhead than the frame relay • Higher layer performs error detection & correction • Anything from 10Mbps to Gbps • Constant data rate using packet switching technique

  11. 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

  12. 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

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

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