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Analog and Digital Transmission

  • Analog Signal:- An analog signal is one that is continuous with respect to time and may take on any value within a given range of values. Human voice, video and music when converted to electrical signal using suitable device produce analog signals. Landline phone uses analog signal.
  • Digital signal:- A digital signal may take on only a discrete set of values within a given range. Most computers and computer related equipment is digital.

Data Flow

Communication between two devices can be Simplex, Half-Duplex, Full-Duplex.
  • Simplex: It is one way data transmission. e.g: pager, radio, T.V
  • Half-Duplex:- In Half-Duplex, each station can both transmit and receive but not at the same time. The half-duplex mode is like a one-lane road with traffic allowed in both direction. e.g: Wireless, Walky-talky
  • Full-Duplex:- In Full-Duplex mode, data can be transmit and receive at the same time. It is a two day data transmission simultaneously. e.g: Telephone, video conferencing etc.

Data Communication Modes

Data can be transmitted from source to destination in a number of ways. The different modes of data transmission are:
  • Parallel and Serial Transmission:- There is always need to exchange commands data and other control information between two communication system There are two option and these are:
    • Serial Transmission:- In Serial transmission bits are transmitted serially, one after another. There are single lines available for this transmission. This a very slow method for transmitting data from one place to another.
    • Parallel transmission:- All the bits of a byte are transmitted simultaneously on separate lines. There are multiple lines available for this transmission. This a very fast method for transmitting data from one place to another.
  • Asynchronous and Synchronous Transmission:- One of the major difficulties in data transmission is that of synchronizing the receiver with the sender. The two mechanisms used for synchronization are:
    • Asynchronous transmission:- Asynchronous transmission sends single character at a time framed by start bit and 1 or 2 stop bits. Each frame begins with a start bit that enables the receiving device to adjust to the timing of the transmitted signal. This transmission is used to transmit character data and is ideally suited for characters that are transmitted at irregular intervals, such as when users are typing in character data from the keyboard.
    • Synchronous transmission:- In synchronous transmission, the whole block of data bits is transferred at once, instead of one character at a time. A sync signal is used to tell the receiving station that a new frame is arriving and to synchronies the receiving station. Synchronous transmission is used when high-volumes of data are to be transmitted.

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