單項(xiàng)選擇題
下面關(guān)于用戶啟動(dòng)(AN側(cè)發(fā)起呼叫)的PSTN的呼叫流程正確的是()。
A、ESTABLISH、ESTABLISHACK、ALLOCATION、ALLOCATIONCOMPLETE
B、ALLOCATION、ALLOCATIONCOMPLETE、ESTABLISH、ESTABLISHACK
C、ESTABLISH、ALLOCATION、ESTABLISHACK、ALLOCATIONCOMPLETE
D、ALLOCATION、ESTABLISH、ESTABLISHACK、ALLOCAT