Introduction - If you have any usage issues, please Google them yourself
because of special operational needs, some telephone exchanges in the surveillance of third parties under the assumption that a telephone exchange was launched by the tripartite B, and C to monitor the controlling party, began to speak when the A, B C can not listen, and began recording at the end when A and C to determine whether or not they can B listen, if we can. B recordings to release, when the B words, to repeat the operation.