Spyros Georgios Zygouris
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  • Circuit Switching Technique

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    In communication networks two quite different switching techniques are used, circuit switching and packet switching. Their difference lies in the way that network nodes shift (forward) the information from one line to the next to reach its destination.
    In circuit switching, to communicate two stations
    an exclusive physical connection is established,
    maintained throughout the communication.
    This connection essentially consists of a series of connections through network nodes.
    Communication with the circuit switching technique involves three phases:
    A. Circuit establishment
    B. Data transfer
    C. Circuit Disconnect
    Station A wants to reach D station.
    To do this, it must first create an end-to-end link (from A to D).
    The connection is implemented partially,
    from A to node K1,
    from node K1 to node K3,
    from node K3 to node K6 and
    from node K6 to D.
    If it is found that D is not busy,
    the connection is established.
    The transfer of information(Data Transfer) can now be started through the network
    from station A to station D.
    This can be analogue or digital,
    depending on the nature of the network.
    Of course, as telecommunications providers,
    on an international scale,
    are developing integrated digital networks,
    the use of digital transmission,
    both for voice and for data,
    has begun to dominate.
    Transmission, which is usually bidirectional (from A to D and D to A)
    is through the line A-K1,
    the internal switching to K1,
    the line K1-K3,
    internal switching to K3,
    line K3-K6,
    internal switching to K6 and
    line K6-D.
    After some time the data transfer ends
    and the connection is terminated.
    The switching nodes that participated
    in this connection are properly updated
    to release the resources
    they have committed.
    These resources
    can be used later
    for another connection.
    Circuit Switching technique can be quite inefficient.
    The capacity of the telecommunication channel,
    a valuable resource of a network,
    is devoted throughout the communication of the two stations,
    even if no information is transmitted.
    For dial-up connection, channel usage is high,
    but it is not approaching 100%
    (there are timeouts moments when the interlocutors are silent).
    For communication between computers
    it is possible for the channel
    to remain unused
    for the longest duration of the connection.
    Also, there is always a delay before transmitting information to restore the connection.
    On the other hand,
    once the connection is restored,
    the information can be transferred
    from one station to another
    at a constant rate
    and without delays
    (unless of course
    by the propagation delay through
    communication lines,
    which is due,
    in that information is transmitted
    at the speed of light,
    which is very large,
    but not infinite).
    The most well-known example
    of a circuit switching network
    is the Public Switched Telephone Network (PSTN).
    Although originally designed and developed
    to provide analogue telephone services to its subscribers,
    PSTN has reached support
    for data transmission (computer connection)
    using appropriate modems,
    and gradually converts to a digital network. Show less
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