During the call of IP-To-PSTN, billing is also divided into two phases.When calls arrives
this gateway, it start send signal to pstn, the billing in the voip side start, but the destination
pstn network just receive the signal. the calls maybe fail or busy. But the voip side doesn’t
know. In order to synchronize those signals in voip and pstn network, this voip gateway
provides the following method, Polarity reversal answer supervision, delay pick up, voice
activity detection.
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In order to use this Polarity reversal signal answer supervision, please make sure the
pstn line has polarity reversal signal enabled.When this voip gateway get ip incoming calls, it
send to pstn line, and it pause the voip message here, and waits the pstn pickup message,
polarity reversal signal. when it get such signal, it continue the voip message.In this way, we
can guarantee the billing of IP side and PSTN side to be consistent.And the ringback tone
from pstn, like color ring can be send to voip side too.
It is under page advance->FXO , item CO line Answer Supervision set to “answer after
receiving reversal signal”, please refer to chapter 5.4.2.
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This Voip Gateway provides answer delay function too. When it send call to pstn, it
pause the voip side signal, just keep sending ring back tone, and wait a pre-defined time and
recover the voip side calls.In some case, it is a way to ease the billing problem. Defaultly the
delay time is 6 seconds. This function is under page page advance->FXO , item CO line
Answer Supervision set to “answer delay”. The delay time is also in the same page.
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This VAD answer supervision will detect the signal on the pstn line after it send the
destination number out. When it detect voice, then it continue the voip calls.
There is also some risk for this type answer supervision. It is easy to detect the periodly
ring tone, but when it get color ring back tone, it possible think it get voice.And this method
need few seconds delay to check the voice.
This function is under page page advance->FXO , item
CO line Answer Supervision set to
“answer after detect voice activety"
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