How TCP Works | tcp receive window | tcp deepdive

The TCP receive window, also known as the receive buffer or the receiver's window, is a mechanism used in TCP to manage the flow of data from the sender to the receiver. It represents the amount of data, in terms of bytes, that the receiver can accept and buffer at a given time.

Here's how the TCP receive window works:

Flow Control: The receive window plays a crucial role in flow control, which ensures that the sender does not overwhelm the receiver with more data than it can handle. The receiver advertises its receive window size to the sender, indicating the amount of available buffer space for incoming data.

Window Size Advertisement: The receiver includes the receive window size in the TCP header of the ACK (acknowledge) packets it sends back to the sender. The window size value represents the number of bytes of data that the receiver can currently accept. It dynamically adjusts based on the available buffer space.

Sliding Window Mechanism: The sender maintains a sliding window that represents the range of sequence numbers it can send without waiting for acknowledgments. The size of the sliding window is determined by the minimum of the receiver's advertised window size and the congestion window size (determined by congestion control mechanisms).

Sending Data within the Window: The sender sends data segments to the receiver as long as the sequence numbers fall within the receiver's window. The receiver acknowledges the received segments and updates its window size accordingly.

Advancing the Window: As the receiver processes and consumes the data, the receive window advances. The receiver informs the sender about the newly available buffer space by updating the window size in the ACK packets it sends.

By managing the receive window, TCP ensures that data transmission is paced according to the receiver's ability to process and store the incoming data. It helps prevent data loss, buffer overflow, and congestion by allowing the receiver to control the rate at which data is sent. The receive window is a crucial component of TCP's flow control mechanism, contributing to the reliable and efficient transfer of data over a TCP connection.