| 释义 |
xDSL (generic Digital Subscriber Line) Reference Model. X.400 gained considerable popularity in Europe, largely for in-house implementations. In the United States, however, the preference developed for the Simple Mail Transfer Protocol (SMTP) of the TCP/IP protocol suite, upon which the Internet is based. Although most carriers do not use X.400 in native implementations, they commonly use it as a gateway protocol for X.400-to-SMTP gateways, particularly for international networks. See also Application Layer, gateway, ITU-T, Layer 7, OSI Reference Model, SMTP, TCP/IP protocol suite, and X Series. |