File Transfer Protocol LOCK Command for Using a Single Port
One of the biggest hurdles for FTP in real life usage is its use of two connections. First, it uses a primary connection to send control commands on, and when it sends or receives data, it opens a second TCP stream for that purpose. This document specifies a new FTP LOCK command to be used by clients to request the server to use the control connection for data transfers, using a single port instead of two.