What are the advantages and disadvantages of synchronous and asynchronous transmission?

Synchronous Transfer

Synchronous transmission is the data transfer in units of data frames. Frame synchronization signals in the form of characters or bit combinations (the latter have high transmission efficiency and reliability) can be used. The transmitter or receiver provides a clock signal dedicated to synchronization. In short distance high-speed large file transfer, the clock signal can be transmitted by a dedicated clock line. When the computer network adopts the synchronous transmission method, the clock synchronization signal is often embedded in the data signal frame to achieve clock synchronization between the receiver and the transmitter.

In digital communication, synchronization is very important. When the transmitter transmits data information to the receiver through the transmission medium, for example, each time a character (or data frame) data signal is sent, the receiver must recognize the start bit and end bit of the character (or frame) data signal. To correctly read each bit of the data signal of the character (or the frame) at the appropriate time, this is the basic synchronization problem between the receiver and the transmitter.

When sengding data signals in data frames, to ensure the integrity and accuracy of the transmitted signal, in addition to requiring the receiver to be able to recognize the start and end of the signal corresponding to each character (or data frame), to ensure that the reading starts and ends at the correct time Retrieving the signal means maintaining the integrity of the transmitted signal. It is also required to keep the clock and the transmitter at the same frequency to ensure that the number of signal units reads per unit time is the same, that is, to ensure the accuracy of the transmitted signal.

Therefore, when transferring data signals in data frames, the transmitter is required to take the following two measures for the transmitted signals:

①  Add a start signal and a stop signal different from the data signal before and after the corresponding signal of each frame of data;

②  Add a clock synchronization signal before the data signal of each frame to control the clock synchronization of the receiver

Asynchronous Transmission

Asynchronous transmission is the transmission of data in units of characters, using character synchronization signals in the form of bits. The transmitter and receiver have independent clocks (the frequency difference cannot be too much), and neither side provides clock synchronization signals to the other side.

The sender and receiver of the asynchronous transmission do not need to coordinate before the data can be transmitted: the sender can move data at any time, and the receiver must be ready to receive data at any time.

The asynchronous transmission mode is generally adopted between the computer host and the input and output devices. Such as a keyboard, a typical RS-232 serial port (used between a computer and a modem or an ASCII terminal device): the sender can send a character at any time (led by a start bit, and then send all the characters in succession, followed by A dumb bit longer than one bit).

The Advantages and Disadvantages of Asynchronous and Synchronous Data Transmission

Synchronous Data Transfer

• Advantages

Improved productivity and transfer rate; no additional time is required to determine the start and finish of the data blocks being sent.

Voice, video, image, and other high-speed, high-capacity, long-duration data transfer applications can all be supported via synchronous transfer.

The benefits of synchronous transfer include easy operation, low transmission costs, great transmission efficiency, and strong dependability.

With synchronous data transfer, high-performance, multifunctional transmission systems are simple to construct.

• Disadvantages

The complexity and cost of synchronous transmission are higher, as it requires a fixed clock signal and additional line cooling.

Higher standards for data format, modulation, and encoding apply to synchronous transmission, necessitating sophisticated synchronizing control mechanisms and high-precision synchronizing devices.

Sophisticated control techniques are necessary for synchronous transmission.

Asynchronous Data Transfer

• Advantages

Asynchronous transmission has a low system overhead, is straightforward to implement, and does not require synchronous clocks.

Asynchronous transmission has no limitations on the frequency or timing of data packet transfer, therefore it can begin delivering data at any moment.

Transmission equipment is appropriate for lower speed and shorter distance communication contexts due to its minimal hardware complexity and inexpensive cost.

The requirements for data structure, modulation, and encoding are less for asynchronous transmission.

• Disadvantages

Because start bits, stop bits, and potential error correction must be included in data packets being transported, some of the data may be erroneous, reducing transmission efficiency.

Asynchronous transfer has lower dependability; data loss is easily possible if data transmission occurs too quickly.

Asynchronous transfer has higher requirements for data integrity and correctness, because there is no fixed interval for data sending and receiving, which can lead to data loss or errors.

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To Sum Up

Both asynchronous transmission and synchronous transmission have the above basic synchronization problem: character synchronization or frame synchronization signals are generally used to identify the start and end of transmitting character signals or data frame signals. The main difference between the two is whether one of the transmitters or receivers sends a clock synchronization signal to the other party.