ISDN用户网络接口规范 第三层基本呼叫控制协议Q.931国家标准（中文）。可以做为ISDN、VOIP H.225的参考资料。-ISDN User Network Interface Specification third tier basic call control protocol Q.931/Network national standards (Chinese). ISDN can be used as a VOIP H.225 reference.