Which field in the TCP header is utilized for flow control?

The window size field in the TCP header is essential for flow control because it specifies the amount of data that the sender is permitted to send before needing to receive an acknowledgment from the receiver. This mechanism helps to prevent network congestion by ensuring that a sender does not overwhelm a receiver with data it cannot process quickly enough.

When a device receives data, it can adjust the window size in its TCP acknowledgments based on its current processing capacity, effectively managing the flow of data according to its ability to receive and handle it. A larger window size indicates that the sender can transmit more bytes before waiting for an acknowledgment, while a smaller window size signals that the sender should pause or slow down transmission to prevent data loss. This dynamic adjustment is fundamental in maintaining efficient and reliable connections in TCP.

Other fields, such as the checksum, are used for error-checking, while the urgent pointer indicates if there are urgent data segments that should be prioritized. The sequence number is crucial for ordering segments within a TCP stream but does not directly influence the flow control mechanism.