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CSCI 465 D ata Communications and Networks Lecture 13

CSCI 465 D ata Communications and Networks Lecture 13. Martin van Bommel. Switching Techniques. Transmission beyond local area requires intermediate switching nodes Nodes concerned not with content but with movement of data

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CSCI 465 D ata Communications and Networks Lecture 13

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  1. CSCI 465Data Communications and NetworksLecture 13 Martin van Bommel CSCI 465Data Communications & Networks

  2. Switching Techniques • Transmission beyond local area requires intermediate switching nodes • Nodes concerned not with content but with movement of data • Two technologies of switching differ in way data is switched from one link to another • circuit switching versus packet switching CSCI 465Data Communications & Networks

  3. Circuit-Switching • Definition: • Communication in which a dedicated communications path is established between two devices through one or more intermediate switching nodes • Dominant in both voice and data today • e.g. PSTN is a circuit-switched network • Relatively inefficient • 100% dedication even without 100% utilization CSCI 465Data Communications & Networks

  4. Circuit-Switching Stages • Circuit establishment • end-to-end circuit established before any signals can be transmitted • Data transfer • point-to-point from endpoints to nodes • internal switching/multiplexing among nodes • Circuit disconnect • deallocate resources dedicated to circuit CSCI 465Data Communications & Networks

  5. PSTN • Public Switched Telephone Network • Four generic components • Subscribers - devices that attach to network • Local loop - link from subscriber to network • Exchanges - switching centers (end office - connected to subscribers) • Trunks - branches between exchanges (FDM or synchronous TDM) CSCI 465Data Communications & Networks

  6. Circuit-Switched Node

  7. Circuit-Switching Node:Digital Switch • Provides transparent signal path between any pair of attached devices • Appears to devices as direct connection • Typically full-duplex CSCI 465Data Communications & Networks

  8. Circuit-Switching Node:Network Interface • Provides hardware and functions to connect digital devices to switch • Analog devices can be connected if interface includes CODEC functions • Typically full-duplex • Trunks to other switches carry TDM signals to provide links for multiple node networks CSCI 465Data Communications & Networks

  9. Circuit-Switching Node:Control Unit • Establishes on-demand connections • handle and acknowledge request • determine if destination is free • construct path through switch • Maintains connection while needed • maintain time-division for connection • Breaks down connection on completion CSCI 465Data Communications & Networks

  10. Blocking/Non-blocking Networks • Blocking • network is unable to connect two stations because all possible paths are already in use (acceptable for voice only) • Non-blocking: • permits all possible connection requests because any two stations can be connected (and may stay that way for a long time) CSCI 465Data Communications & Networks

  11. Switching Techniques • Space-Division Switching • Developed for analog environment, but has been carried over into digital communication • Requires separate physical paths for each signal connection • Uses metallic or semiconductor “gates” • Time-Division Switching • Used in digital transmission • Utilizes multiplexing to place all signals onto common transmission path • Bus must have higher data rate than the individual I/O lines CSCI 465Data Communications & Networks

  12. Circuit-Switched Networks: Routing • Requires balancing efficiency and resiliency • Traditional circuit-switched model is hierarchical, sometimes supplemented with peer-to-peer trunks • Newer circuit-switched networks are dynamically routed: all nodes are peer-to-peer, making routing more complex CSCI 465Data Communications & Networks

  13. Alternate Routing • Possible routes between two end offices are predefined • Originating switch selects the best route for each call • Routing paths can be fixed (one route) or dynamic (multiple routes, selected based on current and historical traffic) CSCI 465Data Communications & Networks

  14. Control Signaling • Manage the establishment, maintenance, and termination of signal paths • Includes signaling from subscriber to network, and signals within network • In-channel signaling uses the same channel for control signals and calls • Common-channel signaling uses independent channels for controls • SS7 – Signaling System Number 7 CSCI 465Data Communications & Networks

  15. Traditional Circuit Switching

  16. Softswitch Architecture • latest trend in circuit-switching technology • computer running specialized software that turns it into a smart phone switch • costs less and provides more functionality • Media gateway (MG) – physical switching • Media gateway controller (MGC) – call processing logic CSCI 465Data Communications & Networks

  17. Softswitch

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