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TCP Congestion Window and Receiver Window
Overview
TCP congestion window (CWND) and receiver window (RWND) are two important mechanisms that regulate the flow of data in TCP connections.
Congestion Window (CWND)
The congestion window is a sender-imposed window that limits the amount of data that a sender can send at any given time. This window is designed to prevent the sender from overwhelming the network and causing congestion.
The CWND is initially set to a small value, and it is gradually increased as the sender receives acknowledgments from the receiver. The sender can continue to send data as long as the CWND is greater than the amount of unacknowledged data.
Receiver Window (RWND)
The receiver window is a receiver-imposed window that limits the amount of data that the receiver can receive at any given time. This window is designed to prevent the receiver from being overwhelmed with data.
The RWND is set to a value that is equal to the amount of buffer space that the receiver has available. The sender must not send more data than the RWND, or the data will be dropped.
Interaction of CWND and RWND
The CWND and RWND interact to regulate the flow of data in TCP connections. The sender can only send data if both the CWND and the RWND are greater than zero.
If the CWND is greater than the RWND, the sender will be limited by the RWND. This can happen if the receiver is slow to process data, or if the network is congested.
If the RWND is greater than the CWND, the sender will be limited by the CWND. This can happen if the sender is sending data too quickly, or if the network is congested.
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