Explain the flow control mechanism?

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11.Explain the flow control mechanism?

Flow control is a fundamental mechanism in data communication that ensures the efficient and reliable transfer of data between a sender and a receiver. It manages the rate at which data is transmitted to prevent data loss, buffer overflow, and congestion. Flow control is especially important when there is a speed or capacity mismatch between the sender and receiver, as it allows them to synchronize their data exchange process. There are two main types of flow control mechanisms: stop-and-wait and sliding window.

flow control mechanism
flow control mechanism


1. Stop-and-Wait Flow Control:

  1.     The stop-and-wait flow control mechanism is a simple and straightforward method to manage data transmission between a sender and a receiver. Here's how it works:
  2.     The sender sends a packet (data frame) to the receiver.
  3.     The receiver acknowledges the receipt of the packet and indicates that it is ready to receive the next packet.
  4.     The sender waits for the acknowledgment before sending the next packet.

If the sender doesn't receive an acknowledgment within a certain timeout period, it assumes that the packet was lost or corrupted and retransmits it. This process continues until the receiver successfully receives the packet and sends the acknowledgment.

The stop-and-wait flow control is effective but not very efficient, especially in high-speed networks, as it introduces a significant delay due to the waiting time for acknowledgments. To improve efficiency, sliding window flow control is used.

2. Sliding Window Flow Control:

    Sliding window flow control is a more sophisticated method that allows multiple packets to be in transit simultaneously, improving data transfer efficiency. The sender maintains a "window" of allowed, unacknowledged packets that it can send to the receiver. The receiver, in turn, maintains a corresponding window to track the expected sequence of packets it can receive.

Here's how sliding window flow control works:

  1.     The sender sends a window of packets to the receiver without waiting for individual acknowledgments for each packet.
  2.     The receiver acknowledges the receipt of packets by sending back an acknowledgment with the number of the next expected packet (acknowledgment number).
  3.     The sender slides the window forward based on the acknowledgment received, allowing it to send additional packets.
  4. The size of the window determines the number of packets that can be sent without acknowledgment. If the window size is too small, the sender may be underutilizing the available bandwidth. If it's too large, congestion and packet loss may occur.


Sliding window flow control optimizes data transfer by allowing continuous transmission, minimizing the waiting time for acknowledgments, and utilizing available network resources efficiently. Different variations of sliding window protocols, such as Go-Back-N and Selective Repeat, are used in various network environments, depending on the requirements and characteristics of the communication channel.

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