| 单词 | X.25 |
| 释义 | X.25 The ITU-T Recommendation for the interface into a packet-switched network, X.25 was pub- lished in 1976, and subsequently revised several times, most recently in 1993. X.25 actually is a protocol suite comprising three layers that map into the bottom three layers of the OSI Reference Model: • packet layer protocol (PLP) maps into Layer 3, the Network Layer • link access procedure, balanced (LAPB) maps into Layer 2, the Data Link Layer • X.21bis maps into Layer 1, the Physical Layer Figure X-1 illustrates the relationship between the PLP, LAPB, and X.21bis. X.25 originally was intended for interactive time-sharing, which involves long connect times and low data volumes over error-prone circuits. Although X.25 still supports such applications effectively, contemporary applications include online interactive processing (e.g., reservations systems and credit card processing), electronic messaging (e.g., e-mail), batch file transfer (e.g., data backup), and Internet access. X.25 largely has been replaced by frame relay and IP networks, although X.25 remains heavily used in developing countries and in areas where error prone analog circuits must be used in data communications applications. See also frame relay, IP, ITU-T, LAPB, packet switch, PLP, protocol suite, X.21bis, and X Series. 74570c24.qxd 9/11/07 12:37 PM Page 548 |
| 随便看 |
|
科学参考收录了5291条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。