Difference Between Flow Control and Error Control

Flow control and Error control are the control mechanism at data link layer and transport layer. Whenever the sends the data to the receiver these two mechanisms helps in proper delivering of the reliable data to the receiver. The main difference between the flow control and error control is that the flow control observes the proper flow of the data from sender to receiver, on the other hand, the error control observes that the data delivered to the receiver is error free and reliable.

Let’s study the difference between Flow control and Error control with a comparison chart.

Content: Flow Control Vs Error Control

1. Comparison Chart
2. Definition
3. Key Differences
4. Conclusion

Comparison Chart

Basis for Comparison	Flow Control	Error Control
Basic	Flow control is meant for the proper transmission of the data from sender to the receiver.	Error control is meant for delivering the error-free data to the receiver.
Approach	Feedback-based flow control and rate-based flow control are the approaches to achieve the proper flow control.	Parity checking, Cyclic Redundancy Code (CRC) and checksum are the approaches to detect the error in data. Hamming code, Binary Convolution codes, Reed-Solomon code, Low-Density Parity Check codes are the approaches to correct the error in data.
Impact	avoid overrunning of receivers buffer and prevents the data loss.	Detects and correct the error occurred in the data.

Definition of Flow Control

The flow control is a design issue at data link layer and transport layer. A sender sends the data frames faster then the receiver can accept. The reason can be that a sender is running on a powerful machine. In this case, even the data is received without any error; the receiver is unable to receive the frame at this speed and loose some frames.

There are two control methods to prevent the loss of frames they are feedback-based flow control and rate-based flow control.

Feedback-based control

In feedback-based control whenever the sender sends the data to the receiver, the receiver then sends the information back to the sender and permits the sender to send more data or inform the sender about how the receiver is doing. The protocols of feedback-based control are sliding window protocol, stop-and-wait protocol.

Rate-based flow control

In rate-based flow control, when a sender transmits the data faster to the receiver and receiver is unable to receive the data at that speed, then the built-in mechanism in the protocol will limit the rate at which data is being transmitted by the sender without any feedback from the receiver.

Definition of Error Control

Error Control is the issue that occurs at data link layer and transport level as well. Error Control is a mechanism for detecting and correcting the error occurred in frames that are delivered from sender to the receiver. The error occurred in the frame may be a single bit error or burst error. Single bit error is the error that occurs only in the one-bit data unit of the frame, where 1 is changed to 0 or 0 is changed to 1.

In burst error is the case when more than one bit in the frame is changed; it also refers to the packet level error. In burst error, the error like packet loss, duplication of the frame, loss of acknowledgment packet, etc. can also occur.The methods to detect the error in the frame are parity checking, cyclic redundancy code (CRC) and checksum.

Parity Checking

In parity checking, a single bit is added to the frame which indicates whether the number of ‘1’ bit contained in the frame are even or odd. During transmission, if a single bit gets changed the parity bit also get change which reflects the error in the frame. But the parity checking method is not reliable as if the even number of bits are changed then the parity bit will not reflect any error in the frame. However, it is best for single bit error.

Cyclic Redundancy Code (CRC)

In Cyclic Redundancy Code the data undergoes a binary division whatever the remainder is obtained is attached with the data and send to the receiver. The receiver then divides the obtained data with the same divisor as with which the sender divided the data. If the remainder obtained is zero then the data is accepted. Else the data is rejected, and the sender needs to retransmit the data again.

Checksum

In checksum method, the data to be send is divided into equal fragments each fragment containing n bits. All the fragments are added using 1’s complement. The result is complemented once again, and now the obtained series of bits is called checksum which is attached with the original data to be send and send to the receiver.

When the receiver receives the data, it also divides the data in equal fragment then add all the fragment using 1’s complement; the result is again complemented. If the result comes out to be zero then the data is accepted else it is rejected, and the sender has to retransmit the data.

The error obtained in the data can be corrected using methods they are Hamming code, Binary Convolution codes, Reed-Solomon code, Low-Density Parity Check codes.

Conclusion

Both the control mechanism i.e. Flow control and Error control are the unavoidable mechanism for delivering a complete and reliable data.