Which action could improve performance when transferring large files to and from a server over FTP?

Increasing the TCP window size can significantly improve performance when transferring large files over FTP. The TCP window size determines how much data can be sent before requiring an acknowledgment from the receiving end. A larger window size allows more data to be "in flight" during the transfer, which is particularly beneficial for transferring large files, as it can lead to better utilization of the available bandwidth and reduced round-trip times.

When the window size is increased, it reduces the need for frequent acknowledgment packets to be sent back and forth, enabling a smoother and faster data transfer. This is especially important in high-latency networks, where each round trip can add significant delays. By maximizing the amount of data sent before waiting for an acknowledgment, the overall transfer speed is enhanced, making it the optimal choice for improving file transfer performance over FTP.