单项选择题
A、ESTABLISH、ESTABLISHACK、ALLOCATION、ALLOCATIONCOMPLETEB……
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