This document discusses asynchronous and synchronous communication. Asynchronous communication transmits data intermittently without an external clock, with timing encoded in the symbols. It is used for variable bit rate applications like file transfers and email. Synchronous communication transmits data in a steady stream at a constant rate, requiring synchronized clocks, but allows more data transfer. It is used for real-time applications like telephone calls. Both methods have advantages and disadvantages related to overhead, speed and clock synchronization.

1. ASYNCHRONOUS
AND
SYNCHRONOUS
..
Prepared by : Parackattu.Akhil.B
Dept : Electronic And Communication

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.  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.  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.  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.  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.  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.  BLOCK DIAGRAM.
sender stop Data Start Receiver
 Here the data is transmitted intermittently rather than in a steady stream.

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.  DRAWBACKS.
• Overhead of start and stop bits.
• Asynchronous transmission is relatively slow due to the increased
number of bits and gaps.

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.  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.  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.  BLOCK DIAGRAM.
Sender DATA Receiver
 Here data is transmitted in a steady stream.

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.  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. THANK YOU…