TCP uses a ______ window that allows for up to 65,576 bytes to be outstanding before it stops and waits for an acknowledgement.

• A. Static window
• B. Dynamic window
• C. Fixed window
• D. Sliding window

Answer: (B)

TCP flow control relies on a sliding window. The sender is allowed to transmit up to the current window size before waiting for an acknowledgement. As the receiver acknowledges data, the window moves forward, making room for more data to be sent. The window size is advertised by the receiver, and because it’s a 16-bit field, the maximum outstanding data is 65,535 bytes (with true implementations often using window scaling to exceed that). This dynamic adjustment of how much data can be in flight is what the sliding window captures. The terms static or fixed imply the window wouldn’t change, which isn’t how TCP flow control works, and dynamic window isn’t the standard name for this mechanism.