What is Flow Control in data link layer

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 Sure! Let’s break down flow control in the Data Link Layer with an example in simple terms.

What is Flow Control?

Flow control is a technique used to manage the rate of data transmission between two devices to ensure that the sender does not overwhelm the receiver. This is crucial because the sender might be capable of sending data much faster than the receiver can process it.

Why is Flow Control Important?

Without flow control, a fast sender could send data at a rate that the slower receiver cannot handle, leading to data loss or the need for retransmission. Flow control ensures smooth communication by regulating the data flow.

Types of Flow Control

There are two main types of flow control mechanisms:

  1. Stop-and-Wait Flow Control
  2. Sliding Window Flow Control

1. Stop-and-Wait Flow Control

In this method, the sender sends one frame and waits for an acknowledgment from the receiver before sending the next frame. This ensures that the receiver has processed the frame before receiving more data.

Example:

Imagine you are sending letters to a friend. You send one letter and wait for your friend to reply before sending the next one. This way, you ensure that your friend has read your letter before you send another.

Steps:

  1. Sender sends a frame.
  2. Receiver receives the frame and sends an acknowledgment.
  3. Sender waits for the acknowledgment before sending the next frame.

Advantages:

  • Simple and easy to implement.
  • Ensures that the receiver is not overwhelmed.

Disadvantages:

  • Inefficient if the propagation delay is high, as the sender spends a lot of time waiting.

2. Sliding Window Flow Control

This method allows the sender to send multiple frames before needing an acknowledgment for the first frame. Both the sender and receiver maintain a window that determines the number of frames that can be sent before an acknowledgment is required.

Example:

Imagine you are sending a series of letters to a friend, but this time you send a batch of letters (say 5) before waiting for a reply. Your friend reads and acknowledges the batch, and then you send the next batch.

Steps:

  1. Sender sends multiple frames up to the window size.
  2. Receiver receives the frames and sends cumulative acknowledgments.
  3. Sender slides the window forward based on the acknowledgments received and sends the next set of frames.

Advantages:

  • More efficient than Stop-and-Wait as it reduces waiting time.
  • Better utilization of the network.

Disadvantages:

  • More complex to implement.
  • Requires more memory and processing power.


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