http://www.rfc-editor.org/rfc/rfc0877.txt
RFC 0877: Standard for the transmission of IP datagrams over public data networks, J.T. Korb1983-09-01T23:00:00-00:00This RFC specifies a standard adopted by CSNET, the VAN gateway, and other organizations for the transmission of IP datagrams over the X.25-based public data networks.