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Asynchronous and synchronous


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comparison between Asynchronous and Synchronous

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Asynchronous and synchronous

  1. 1. ASYNCHRONOUS AND SYNCHRONOUS .. Prepared by : Parackattu.Akhil.B Dept : Electronic And Communication
  2. 2.  NEED OF SYNCHRONIZATION. • Whenever an electronic device transmits digital (and sometimes analogue) data to another electronic device. • There must be a certain rhythm established between the two devices, i.e., the receiving device must have some way of knowing, within the context of the fluctuating signal that it's receiving. • where each unit of data begins and where it ends. • So there two types synchronization. i. Asynchronous. ii. Synchronous.
  3. 3.  ASYNCHRONOUS. • In asynchronous the transmission of data is generally without the use of an external clock signal, where data can be transmitted intermittently rather than in a steady stream. • Any timing required to recover data from the communication symbols is encoded within the symbols. • The most significant aspect of asynchronous communications is that data is not transmitted at regular intervals, thus making possible variable bit rate. • And that the transmitter and receiver clock generators do not have to be exactly synchronized all the time.
  4. 4.  PHYSICAL LAYER. • In asynchronous serial communication the physical protocol layer, the data blocks are code words of a certain word length. • For example octets (bytes) or ASCII characters, delimited by start bits and stop bits. • A variable length space can be inserted between the code words. No bit synchronization signal is required. • This is sometimes called character oriented communication.
  5. 5.  TWO CATEGORIES OF ASYNCHRONOUS. • Strobe Control. • Handshaking Control. Strobe control. • This is one way of transfer i.e. by mean of strobe pulse supplied by one of the units to indicate to the unit when the transfer has to occur. Handshaking control. • This method is used to accompany each data item being transferred with a control signal. That indicates presence of data into the bus.
  6. 6.  STROBE CONTROL METHOD. • Strobe control method of data transfer uses single control signal for each transfer. • The strobe may be activated by either source unit or destination unit Source Unit Destination Unit Data bus Strobe
  7. 7.  HANDSHAKING CONTROL METHOD. • In case source unit the data transfer under the strobe. The source unit has no way of knowing whether destination unit has received the data or not • Similarly destination has no way of knowing whether source unit has place data on the data bus or not • So handshaking mechanism solve this problem by introducing second control signal that provides a reply to unit that initiates to transfer. Source unit Data Unit Data valid Data Bus Data Accepted
  8. 8.  BLOCK DIAGRAM. sender stop Data Start Receiver  Here the data is transmitted intermittently rather than in a steady stream.
  9. 9.  APPLICATION. • Asynchronous activities take place outside of real time system. • As asynchronous does not require a constant bit rate. • For examples file transfer, email and the World Wide Web.
  10. 10.  DRAWBACKS. • Overhead of start and stop bits. • Asynchronous transmission is relatively slow due to the increased number of bits and gaps.
  11. 11.  SYNCHRONOUS. • In Synchronous the transmission of data is sent in a continuous stream at a constant rate. • Synchronous communication requires that the clocks in the transmitting and receiving devices are synchronized running at the same rate. • so the receiver can sample the signal at the same time intervals used by the transmitter. No start or stop bits are required. • For this reason synchronous communication permits more information to be passed over a circuit per unit time.
  12. 12.  TWO CATEGORIES OF SYNCHRONOUS • Byte oriented protocols • Bit oriented protocols Byte Oriented Protocol. • Early synchronous protocols were byte-oriented protocols, where synchronization was maintained by transmitting a sequence of synchronous idle characters. • when the line was not actively transmitting data or transparently within a long transmission block. • This protocol was developed by IBM in late 1960.
  13. 13.  BIT ORIENTED PROTOCOL. • Bit-oriented protocols are synchronous protocols that view the transmitted data as a stream of bits with no semantics, or meaning. • Control codes are defined in terms of bit sequences instead of characters. Synchronization is maintained on an idle line by transmitting a predefined sequence of bits. • Synchronous Data Link Control (SDLC) specifies that a station continue transmitting a sequence of '1' bits on an idle line.
  14. 14.  BLOCK DIAGRAM. Sender DATA Receiver  Here data is transmitted in a steady stream.
  15. 15. • Over time the transmitting and receiving clocks will tend to drift apart, requiring resynchronization. • Synchronous communication is direct communication that occurs in real time. • That take place face-to-face, and as technology has evolved, can take place irrespective of distance • (ex. telephone conversations and instant messaging)
  16. 16.  APPLICATION. • Most common use is in the ASCII terminals. • High speeds communication links established using synchronous modems. DRAWBACKS. • The clock frequency should be same at both the sending and receiving ends. • No tolerance in clock frequency is allowed.
  17. 17. THANK YOU…