ARPA service
The ARPA services support the most important applications based on the TCP/ IP protocols. They are located in layers 5 to 7 and apply to both the TCP protocol and the User Datagram Protocol( UDP).
The connection-oriented Transmission Control Protocol (TCP) is the basis for the application protocols for virtual terminal traffic, for file transfer the FTP protocol and for electronic mail the Simple Mail Transfer Protocol( SMTP), as well as X-Window.
The connectionless UDP protocol supports the Trivial File Transfer Protocol( TFTP) and the Simple Network Management Protocol( SNMP).