© N. Ganesan, Ph.D. , All rights reserved.

Chapter

Asynchronous and Synchronous Transmission

Chapter Objectives

• Explain the features of asynchronous and synchronous transmission and possible areas of application for each transmission type

Chapter Modules

• Asynchronous Transmission• Synchronous Transmission

© N. Ganesan, Ph.D. , All rights reserved.

Module

Asynchronous Transmission

Questions

• What is the characterizing feature of asynchronous transmission?

• Give some examples of asynchronous transmission

• Can asynchronous transmission be conducted at high and low speeds? Give examples in each case

Asynchronous Transmission

• Burst mode transmission• Sender and receiver are not

synchronized with respect to the flow of the information

• However, the sender and receiver are synchronized with respect to the timing of the characters that are transmitted

A Note on Asynchronous Transmission

• In the past, asynchronous transmission referred only to character by character transmission where each character contained information about timing etc.– Note the use of start and stop bits

• At present, the concept of asynchronous transmission can be extended to cover packet transmissions as well

The Use of the Word Asynchronous

• Asynchronous Transmission– Generally refers to the transmission

of characters with each character carrying information about timing

• Asynchronous Communication – Refers to overall communication

between two points • An example in this case would be ATM

Asynchronous Transmission Applied to Characters

Stop Bit Start Bit

Each character is individually timed.

Character Frame

Asynchronous Transmission Applied to

Packets

Packets of data Packets of data

Burst of Data

A B

Intermittent transmission of packets of data

Analogy

Host expecting thearrival of guests

Intermittent of burst arrivalof guests

Asynchronous Transmission/Communication

Application

• Character by character transmission

• Data packet transmission at present

Speed Variations In Asynchronous Transmission

• Low and high-speed transmissions are possible

• Low speed– Almost all modem based communications

fall into this category

• High speed– Asynchronous Transfer Mode (ATM)

• Internet is a good example where asynchronous communication is used predominantly to carry the information

Questions

• What is the characterizing feature of asynchronous transmission?

• Give some examples of asynchronous transmission

• Can asynchronous transmission be conducted at high and low speeds? Give examples in each case

End of Module End of Module

© N. Ganesan, Ph.D. , All rights reserved.

Module

Synchronous Transmission

Questions

• How does synchronous transmission differ from asynchronous transmission?

• Where is synchronous transmission used in practice?

Synchronous Transmission• Sender and receiver are synchronized

with respect to the sending and receiving of information

• Each character need not have a start-bit and a stop-bit as the sender and the receiver are both synchronized

• Requires more hardware and software resources

• High speed communication is the norm

A Note on Synchronous Transmission

• The definition of synchronous transmission refers to the transmission of characters

• However, the use of the word synchronous can be extended to cover packet transmission as well

Usage in Practice

• Which one of the two transmissions is used widely in the real world? Explain.

Examples of Synchronous Transmission

• High-speed communication links established using synchronous modems– It is now possible to establish high speed

links based on asynchronous transmission

• Used in a number of mainframe installations– Collective exchange of information between

the mainframe and the peripheral devices is based on synchronous transmission

In Summary

• Synchronous transmission plays a smaller role compared to asynchronous transmission in practice

• Implementation of synchronous transmission requires more resources

• Asynchronous technology has advanced– It is no more necessary to rely on

synchronous communication to establish a high speed communication link

End of Module End of Module

End of ChapterEnd of Chapter