求助：有谁了解early-ACM message?

兰兰

最近接到一个客户的问题：
The early-ACM message is an ISUP message send from the terminating exchange to the originating exchange as soon as an IAM message is received from the originating exchange
under what conditions, the early-ACM message can be sent?

谁能帮帮我？
我搜索了一下ISUP协议，找不到关于early-ACM message的内容，HELP！！！