TIdEchoUDPServer = class(TIdUDPServer);

TIdEchoUDPServer is a TIdUDPServer descendant that implements the UDP-based variant of the Echo Protocol, as described in the Internet Standards document: 

RFC 862 - Echo Protocol  

TIdEchoUDPServer is useful as a debugging and measurement protocol where the data sent to the server is simply sent back to the originating client. The ECHO protocol provides a measure of the time it takes to send and receive data from an Echo Server (TIdEchoUDPServer). 

The UDP-based implementation of the Echo Protocol server is not a connection based application. 

An Echo Server listens for TCP connections on TCP Port 7. 

The UDP server listens for the arrival of datagrams, and any data received by the server is returned to the originating client. 

Set the value in DefaultPort to indicate the port assigned for listener threads in the server. 

Definitions for socket handles can be added to Bindings, and used to created one or more listener threads when the Active property in the server is set to True. 

TIdEchoUDPServer overrides the protected method executed an arriving datagram on a socket handle for a a listener thread is detected. Data read from the socket handle is written to the originating IP address and port number for the datagram.