The Echo protocol (Echo) is a "testing" protocol, used to verify proper return of data from a server. When contacted, the server responds by echoing back unaltered all data as received. The protocol is quite useful for verifying that no data corruption is occuring at any point during the round trip. Interestingly, most versions of Microsoft Windows contain a built-in Echo server that can be easily activated. Echo servers can be accessed using a TelNet client. Below are addresses to various free public access Echo servers.
[IANA Port assignment = 7]