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The voltage is too low cause U1930 cannot recognize DTMF signal

Publication Date:  2014-08-31 Views:  141 Downloads:  0
Issue Description
Topology:  U1930 ---- AT0 ---- PSTN
When somebody make an incomming call to the automatic switchboard, the caller will not be forwarded to the extension after pressing the extension number. after pressing the extension number, the caller number still got the VU announcement , it seems that U1930 didn't know the caller has dialed any key.
Alarm Information
Handling Process
1. Make a call from internal extension to mobile. after the call connected, press "0" ~ "9" on the mobile.

In this test: at the internal extension we can hear the DTMF signal when pressing any key. this shows that operator has sent DTMF signal to U1930.

2. start captures on the IP phone, and try test 1 again. after the call finishing, stop and analysis the captures.
DTMF signal has included in this captures.

3. got the media stream in the capture, and analysis the voice by tool. resutl as below screenshot: from which we know that the voltage only -29 db.

4. Run command "show mrspara" on U1930, from the result we know the lowest voltage is -23 db.

5. Run command "config modify mrsparas dtmfthrshlevll -36" to modify the lowest voltage as -36 db and test again. problem solved.
Root Cause
From the phenomenon we think U1930 didn't regonize the DTMF signal, there are 2 possible resason:
 1. there is something wrong on the operator devices , when the mobile pressing keys, operator didn't send DTMF signal to U1930.
 2. Operator send DTMF signal to U1930, but the parameters is not standard (voltage, frequence) , cause U1930 receive it but cannot regonize it.