BY

AJAL.A.JFACULTY – METS

Transmission Mode

INTRODUCTION

Transmission Modes

Parallel Mode is the way the internal transfer of binary data takes place inside a computer.

Serial Mode is the predominant method of transferring information in data communications.

Transmission ModesParallel Mode

Serial Mode

Baseband Transmission

Digital transmission is the transmission of electrical pulses. Digital information is binary in nature in that it has only two possible states 1 or 0.

Digital signals are commonly referred to as baseband signals.

In order to successfully send and receive a message, both the sender and receiver have to agree how often the sender can transmit data (data rate).

Parallel Bits in a group are sent simultaneously, each using a

separate link n wires are used to send n bits at one time Advantage: speed Disadvantage: cost; limited to short distances

Serial Transmission of data one bit at a time using only one

single link Advantage: reduced cost Disadvantage: requires conversion devices Methods:

Asynchronous Synchronous

Asynchronous Transmission

Transfer of data with start and stop bits and a variable time interval between data units

Timing is unimportant Start bit alerts receiver that new group of data is arriving Stop bit alerts receiver that byte is finished Synchronization achieved through start/stop bits with each byte

received Requires additional overhead (start/stop bits) Slower, ideal for low-speed communication when gaps may occur

during transmission (ex: keyboard) Cheap and effective

Asynchronous Transmission

In asynchronous transmission, we In asynchronous transmission, we send 1 start bit (0) at the beginning send 1 start bit (0) at the beginning

and 1 or more stop bits (1s) at the end and 1 or more stop bits (1s) at the end of each byte. There may be a gap of each byte. There may be a gap

between each byte.between each byte.

Note:Note:

Asynchronous here means Asynchronous here means “asynchronous at the byte level,” but “asynchronous at the byte level,” but the bits are still synchronized; their the bits are still synchronized; their

durations are the same.durations are the same.

NoteNote::

Synchronous Transmission

Requires constant timing relationship Bit stream is combined into longer frames, possibly containing

multiple bytes Any gaps between bursts are filled in with a special sequence of

0s and 1s indicating idle Advantage: speed, no gaps or extra bits Byte synchronization accomplished by data link layer

Synchronous Transmission

In synchronous transmission, In synchronous transmission, we send bits one after another without we send bits one after another without

start/stop bits or gaps. start/stop bits or gaps. It is the responsibility of the receiver to It is the responsibility of the receiver to

group the bits.group the bits.

Note:Note: