说明：  ISUP协议规范，对于学习ISUP协议，阅读规范是一个不错的方法。尤其对于深入的理解协议，阅读规范是一个不错的手段。
(ISUP protocol specification ISUP protocol for studying, reading norms are a good way. Especially in-depth understanding of the agreement, read the specification is a good means.)