| 摘要 |
A time switch is disposed between a calling terminal and a called terminal to changeably form a communication loop with respect to an established call, so as to determine the origin of a call failure. For example, when only the calling party hears a voice from the called party, and the called party may not hear any voice, the time switch connects the output of the calling party to the input of the calling party itself to determine whether or not the calling party can hear their own voice. If the calling party can hear their voice, it will be determined that the call failure does not originate from the calling party. The time switch then connects the output of the called party to the input of the called party itself to determine whether or not the called party can hear their own voice. If the called party can not hear their voice, it will be determined that the call failure originated from the called party.
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