Specific method of establishing Intranet with DDN and PSTN to join center LAN to remote LAN each other is accomplished,in which we use PSTN as backup connection of DDN to assure the transmission is not interrupted. It is of practical use.

• 利用 DDN、PSTN组建企业级 Intranet；实现中心局域网与远程局域网的互联 ；且使用 PSTN作为 DDN专线的备分线路 ；保证网络传输不中断 ；具有实用价值 .