Difference between flow control and error control

Key difference - Flow control vs error control

Data communication is the process of sending data from source to destination via a transmission medium. For effective communication of data, it is necessary to use techniques. The transmitter and receiver have different speeds and storage capacities. When the data reaches the destination, it is temporarily stored in memory. This memory is called a buffer. Differences in speed and buffer limits can affect the reliability of data communication. Flow control and error control are two different mechanisms used for precise data transmission. If the speed of the transmitter is higher and the speed of the receiver is lower, there is a speed offset. Then, the data flow sent must be checked. This technique is called flow control. Errors may occur during transmission. If the recipient identifies an error, he must inform him of the presence of an error in the data. Thus, the sender can retransmit the data. This technique is known as error checking. Both occur in the data link layer of the OSI model. the Both occur in the data link layer of the OSI model. the Both occur in the data link layer of the OSI model. the key difference between flow control and error control is that flow control is about keeping the correct data flow from sender to recipient, while error control is about determining whether the data being passed to the receiver are reliable and error free.

What is flow control ??

When sending data from one device to another, the sender is called a source, sender, or sender. The recipient is called the recipient or recipient. The sender and the recipient can have different speeds. The recipient will not be able to process the data if the speed of sending the data is higher. Thus, flow control techniques can be used.

A simple method of flow control is, Stop and Wait Flow Control . First, the transmitter sends the data frame. Upon receipt, the recipient sends an acknowledgment frame (ACK). The transmitter can send data only after receiving the acknowledgment frame from the receiver. This mechanism controls the transmission flow. The main disadvantage is that you can only transmit one frame of data at a time. If a message contains more than one frame, stopping and waiting will not be an effective flow control method.

In Sliding Window Method , both the sender and the recipient hold a window. The window size can be equal to or less than the size of the buffer. The sender can transmit until the window is full. When the window is full, the transmitter must wait to receive an acknowledgment from the receiver. A sequence number is used to track each image. The receiver acknowledges a frame by sending an acknowledgment with the sequence number of the next expected frame. This acknowledgment announces to the sender that it is ready to accept the size of the number of images window, starting with the specified number.

What is error checking?

Data is sent as a sequence of frames. Some images may not reach the destination. The burst of noise may affect the frame and therefore may not be recognizable by the recipient. In this situation, this is called the frame is lost. Sometimes the frames reach the destination, but there are bit errors. Then the frame is called a damaged frame. In both cases, the recipient does not receive the correct data frame. In order to avoid these problems, the sender and the recipient have protocols for detecting transit errors. It is important to transform the unreliable data link into a reliable data link.

Error checking techniques

There are three error control techniques. They are Stop-and-Wait, Go-Back-N, Selective-Repeat. Together, these mechanisms are known as the Automatic Repeat Request (ARQ).

In Stop and wait for ARQ, a frame is sent to the recipient. Then the recipient sends the acknowledgment. If the sender has not received an acknowledgment within a specified time, it will send this frame again. This period is determined using a special device called a timer. When the frame is sent, the sender starts the stopwatch. He has a fixed time. If there is no recognizable acknowledgment of receipt from the recipient, the sender will retransmit this frame again.

In Go-Back-N ARQ, the sender transmits a series of images up to the size of the window. If there is no error, the recipient sends the acknowledgment as usual. If the destination detects an error, it sends a negative acknowledgment (NACK) for this frame. The receiver will discard the error frame and all future frames until the error frame is corrected. If the sender receives a negative acknowledgment, it should retransmit the error frame and all subsequent frames.

 In ARQ Selective Repeat , the receiver keeps track of the sequence numbers. It sends a negative acknowledgment from the only lost or damaged frame. The sender can only send the frame for which the NACK is received. It is more effective than Go-Back-N ARQ. These are the common error checking techniques.

Similarity between flow control and error control?
..... Flow control and error control occur in the data link layer.

What is the difference between flow control and error control?

Flow control vs error control

Flow control is the mechanism for maintaining correct transmission from sender to recipient in data communication. Error control is the mechanism for transmitting reliable and error-free data to the receiver during data communication.
 Main techniques
Stop and Wait and Sliding Window are examples of flow control techniques. ARQ Stop-and-Wait, ARQ Go-Back-N, ARQ selective-repeat are examples of error control techniques.


Summary - Flow  Control vs error control

The data is transmitted from the sender to the recipient. For reliable and effective communication, it is essential to use techniques. Flow control and error control are two of them. This article discusses the difference between flow control and error control. The difference between flow control and error control is that flow control is to maintain the correct data flow from sender to recipient, while error control is to determine whether the data being transmitted to the receiver are reliable and error free.

Reference:
1. "Flow control (data)". Wikipedia, Wikimedia Foundation, January 27, 2018. Available here
2.Point, tutorials. "DCN data link control and protocols.", Tutorials Point , January 8, 2018.  Available here 
3.nptelhrd. Lecture - 16 Flow and error control, Nptelhrd, Oct. 20, 2008.  Available here

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