下面关于用户启动(AN侧发起呼叫)的PSTN的呼叫流程正确的是()
A.ESTABLISH、ESTABLISH ACK、ALLOCATION、ALLOCATION COMPLETE
B.ALLOCATION、ALLOCATION COMPLET
C.ESTABLISH、ESTABLISH ACK
D.ESTABLISH、ALLOCATION、ESTABLISH ACK、ALLOCATION COMPLETE
E.ALLOCATION、ESTABLISH、ESTABLISH ACK、ALLOCAT