25 protocol and its application in CHINA then Summarizes the progress of X. 25 synchronous communication controller . At last a key device for microcomputers to jon PSDN - a high-performance intelligent X.

介绍X25 协议及其在中国的应用情况，对X.25同步通信控制器的发展进行了总结和分析，给出一种微机加入公用数据网关键设备&高性能的智能 X.25 同步通信控制设备的设计。

L2TP VPN as a second layer of VPN technology because of simple can support multi-protocol ( which can carry IP X.25 frame relay or ATM ATM point-to-point protocol frames ) and many other advantages in the VPN market occupy an important role .

L2TPVPN作为第二层的VPN技术，由于简单易行，可支持多协议（可承载IP、 X.25、帧中继或异步传输模式ATM的点对点 协议帧）等诸多优点在VPN市场上占有重要角色。