File Service Protocol
File Service Protocol is a UDP-based replacement for the File Transfer Protocol, designed for anonymous access with lower hardware and network requirements than FTP. In particular, because it uses UDP, it avoids the problems that many FTP servers have had with requiring a separate process for each client, and because it is built to use an unreliable protocol, it can more easily handle resuming a transfer after a network failure.
History
FSP never reached the popularity of FTP for legitimate use, but became very popular in the early-to-mid-1990s for underground sites containing pornography and/or warez. Because an FSP server only requires one process, it is much harder for a system administrator to notice it in a process list; also, since it uses UDP, it is less likely to be noticed by a network administrator.Eventually, however, an increased use of firewalls, a decreasing usage of the shell accounts required to run a server or most of the clients, and a lack of FSP support in web browsers caused its use to taper off, and the warez scene moved to HTTP and FXP while pornography moved to publicly advertised web servers.