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Sliding Window Protocol

What is Sliding Window Flow Control?

Sliding Window Flow Control is a mechanism that controls the flow of data between a sender and a receiver. It prevents the sender from overwhelming the receiver with too much data at once and ensures that data is transmitted efficiently.

Key Concepts

  1. Window Size:

    • The "window" represents the amount of data (in bytes or packets) that the sender can send before requiring an acknowledgment (ACK) from the receiver.
    • Both the sender and receiver agree on the window size beforehand.

  2. Acknowledgments (ACKs):

    • The receiver sends an acknowledgment to confirm the successful receipt of data.
    • The sender uses these acknowledgments to decide how much more data to send.

  3. Sliding Mechanism:

    • As the receiver acknowledges packets, the sender’s window "slides" forward, allowing it to send additional packets.

How It Works

  1. Initial Transmission:

    • The sender transmits packets up to the window size limit.
    • For example, if the window size is 4 packets, the sender sends packets 1, 2, 3, and 4.

  2. Waiting for Acknowledgments:

    • The sender waits for ACKs from the receiver.
    • If the receiver acknowledges packet 1, the window slides forward, allowing the sender to send packet 5.

  3. Retransmission:

    • If a packet is lost or corrupted, the receiver does not acknowledge it.
    • The sender retransmits the lost packet once it detects the missing acknowledgment.

Types of Sliding Window Protocols

  1. Go-Back-N (GBN):

    • If a packet is lost, the sender retransmits the lost packet and all subsequent packets in the window, even if some were already received correctly.

  2. Selective Repeat (SR):

    • The sender retransmits only the lost or corrupted packets.
    • This method is more efficient but requires the receiver to store out-of-order packets.

Advantages of Sliding Window Protocols

  • Efficiency: Sliding Window allows multiple packets to be in transit simultaneously, maximizing the use of available bandwidth.

  • Error Handling: Mechanisms like Go-Back-N and Selective Repeat ensure reliable communication.

  • Flow Control: Prevents the receiver's buffer from being overwhelmed by regulating the rate of data transfer.

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