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、ESTABLISHACK、ALLOCATION、ALLOCATIONCOMPLETE
B:ALLOCATION、ALLOCATIONCOMPLETE、ESTABLISH、ESTABLISHACK
C:ESTABLISH、ALLOCATION、ESTABLISHACK、ALLOCATIONCOMPLETE
D:ALLOCATION、ESTABLISH、ESTABLISHACK、ALLOCAT
出自:电信业务技能