Asyn Sync Transmission
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Transcript of Asyn Sync Transmission
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Communication Modes
There are three communication modes.
Simplex Communication
Sender Receiver
Only One-way communication is possible.
Examples : TV, Radio
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Communication ModesHalf Duplex
Sender
Receiver
Two-way communication is possible, but
not simultaneously.
ExampleWalky Talky.
Receiver
Sender
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Communication ModesFull Duplex
Sender
Receiver
Two-way simultaneous communication is
possible.
ExampleTelephone System.
Receiver
Sender
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Serial Transmission
Data are transmitted in a bit by bit fashion.
1 0 0 1 1 1 0 1 0 0 0 0 0 1 0 1
Only one channel is needed for the link.
Used in almost all the data communication
applications.
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Parallel Transmission
1
0
0
11
1
0
1
0
0
0
00
1
0
1
All the bits in a
byte or a wordare transmitted
simultaneously
Because of the need of the multiple channels,
only used to connect devices in short range.
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Synchronization
Since the information is encoded into digital
signals at the transmitting side, for the receiver
to interpret the incoming information correctly,
the receiver must be able to identify the exact
boundaries of each bit, each byte, and each
block of information.
Enabling this capability in a transmission link
is called synchronization.
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Synchronization Ctd.
Synchronization in a transmission link isachieved in three levels.
Bit or Clock Synchronization
Byte or Character Synchronization Block or Frame Synchronization.
There are two approaches followed in common
practice. Asynchronous Transmission
Synchronous Transmission
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Asynchronous Transmission
The bit rate is known in advance by bothtransmitting and receiving ends.
The level of the link is maintained at high
when no bits are transmitted.
The number of data bits, use and the type of
the parity bit, and the number of stop bits are
also agreed upon in advance, and each
transmitted element (byte, character,etc.) is
encapsulated with a Start bit and one or more
Stop bits.
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Asynchronous Transmission Ctd.
Start of Transmission Time
Start Bit 8data bitsEven Parity Bit
Stop Bit(s)
1 1 0 0 0 1 0 1
Direction of Transmission
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
1st
Byte 2nd
Byte
1 1 0 0 0 1 0 1 1 0 0 0 0 1 0 1
Direction of Transmission
Asynchronous Transmission Ctd.
Start BitStart Bit
Stop Bit(s) Stop Bit(s)
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Asynchronous Transmission Ctd.
The bit rates known by the both ends
enable the Bit or Clock synchronization.
The use of start and Stop bits enables theByte or Character synchronization.
The communication control characters
such as STX, ETX are used to achievethe Block or Frame synchronization.
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Asynchronous Transmission Ctd.
When one Start bit, one Parity bit and
one Stop bit is used for each transmitted
element, for example a byte, the actual
throughput can be examined by the
efficiency.
A synchronous transmits is used forlow bit rate character based
communication.
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Synchronous Transmission
This is a method used to transmit data in amore efficient manner.
There are no gaps or extra bits placed inbetween the transmitted bytes.
A complete frame containing the dataelements to be transmitted is constructed andthe frame is transmitted as a single entity.
There are two approaches, namely
a) Character Oriented SynchronousTransmission
b) Bit Oriented Synchronous Transmission
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Synchronous Transmission
SYN SYN STX STX
Data and Error Detection Info.
Direction of Transmission
Frame
SYNSynchronizing Character
STXStart of Text
ETXEnd of Text
Character Oriented Synchronous Transmission
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Synchronous Transmission Character Oriented Synchronous
Transmission with Character Stuffing
SYN SYN DLE STX DLE STXDLE DLE
Start of Text sequence End of Text sequence
DLE inserted by
the transmitter
This scheme is made data-transparent by
Character Stuffing.
Frame Content
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Synchronous Transmission
Bit Oriented Synchronous Transmission
01111110 1001110111111. ..110110 01111110
Opening Flag Closing Flag
Frame Content
Frame
Opening Flag is used to achieve Byte or
Character synchronization
Clock information is included within the
encoding method and hence the Bit or Clock
synchronization is achieved.
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Synchronous Transmission
Bit Oriented Synchronous Transmission withBit Stuffing
01111110 10011101111101..11011011 01111110
Zero bit inserted
The Zero Bits inserted by the transmitter
after every set of consecutive five binary 1sin the content, to avoid the date being mis
interpreted go the opening flag.
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Dales Delivery Services
There are two types of Services :
a) Connection-Oriented Services
b) Connectionless Services
In connection Oriented Services, a continues
path from the source to the destination is
established, then it is used for the information
transfer and finally it is released.
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Types of Services Ctd.
In Connectionless services, there is no continues
path established between the source and the
destination, instead the transmitted information
are encapsulated in packets which contain thefull addressing information of the destination.
The addressing information enables the
connecting devices in the network to forward
the packets on the correct routes so that the
packets can reach the destination.
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Types of Services Ctd.
Each service can be characterized by a Quality of
Service.
Some services are characterized as reliable as they
guarantee that the data are delivered correctly to
the destination. Such services provide some means
of acknowledgement which confirms the correctreception. Convection oriented services are
typically reliable.
The services which do not provide suchacknowledgements are known as unreliable (best
effort) services. Convectional services are typically
unreliable.
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Flow Control
Involved with controlling the flow of
information so that the receiver can accept all
the information without any overflow or loss
due to the fact that the sender is sending at ahigher speed.
The implementation of Flow Control requires
some kind of feedback mechanism, so the
sender can be made aware of whether or not
the receiver can keep up.
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Unrestricted Simplex Protocol
This is the simplest - But unrealistic !!!
It is based on the following assumptions.
Data are transmitted in one direction only.Both transmitting and receiving sides are
always ready.
Processing time can be ignored.The communication channel is totally error
free and does not cause any data losses.
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Unrestricted Simplex protocol
Is a
Frame
Coming?
Receive it
Yes
NoFrameReady to
send?
Send it
Yes
No
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Simple Stop-and Wait Protocol
Is a
Frame
ready?
Is the
Receiver
Ready?
No
YesNoYes
Send
the frame
At the Sender :-
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Simple Stop-and Wait Protocol
Is theprocessingof framecompleted?
No
YesNo
YesProcessthe frame
At the Receiver :-
Is thenext framearrived?
Send anacknowle-dgement
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ICT 2002. All rights reserved. No part of this material may be reproduced and sold.
Sliding Window Protocols
More frames are sent without waiting for
individual acknowledgements.
The number of frames sent at a time can be
changed dynamically.
Sender maintains a set of sequence numbers
corresponding to the frames it is permitted tosend. (Sending Window)
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Receiver also maintains a Receiving Windowcorresponding to the set of frames it is
permitted to accept.
The Senders Window and the ReceiversWindow need to have the same lower and upper
limits.
Slid window to protocol is more efficient thenthe stop & wait protocol
Slid window protocol is used in connation
oriented service typically.
Sliding Window Protocols Ctd.