Transmission Modes

Transmission Modes

The transmission mode enables the receiving computer to know where one byte ends and the next byte begins on the transmission medium. The two transmission modes are: -

. Asynchronous Transmission
. Synchronous Transmission

Asynchronous Transmission

Asynchronous Transmission is also called as start and stop transmission. In this case a sender can send a character at any time convenient and the receiver will accept it. In this case data is transmitted character by character at irregular intervals. Each character is preceded with a start bit and succeeded with a stop bit.

This kind of transmission is well suited for keyboard type terminals and tape devices. The advantage of using this kind of transmission is that it does not require any local storage at the computer. Therefore it is economical to implement.

The main disadvantage of using asynchronous transmission is the idle time during character transmission.

Synchronous Transmission

In case of Synchronous Transmission, it involves a group of characters in the form of a block and each block is framed by a header and trailer information. The header contains synchronizing information used by the receiving device to set the clock time in synchronize with the clock time of sender. The trailer consists of information about sender and receiver, this kind of transmission is well suited for remote communication between a computer and devices such as buffered card reader and printers. Here the block length is about 80-130 characters long. It is also used with buffered terminals for communication in a network. The primary advantage of using synchronous transmission is efficiency because it offers higher data rate and lesser time difference between the blocks as compared to asynchronous transmission.