A.17userbusy
B.18nouserresponding
C.19noanswerfromtheuser
D.20subscriberabsent
A.IAM
B.APM
C.ACM
D.ANM
A.A.Call Instance Code(CIC):呼叫实例码,表示一次呼叫信令的关系
B.B.Bearer setup direction:承载建立方向,指示前向或者后向承载
C.C.BICC tunneling:在CS2中,支持IP承载。IP承载控制协议通过BICC隧道传送
D.D.Codec negotiation:通过IAM、APM等消息,协商Codec