Secondary Digit Collecting Failure Caused by Low Signal Voltage During Transfer from the Automatic Switchboard to the Extension Telephone
Symptom
Network: eSpace U1930----AT0----PSTN
An outer-office mobile user makes a call to the VU automatic switchboard. The call cannot be transferred to the extension telephone. There is no response after the user dials the extension number. The calling party still hears the VU announcement.
Possible Cause
Based on the symptom, the eSpace U1930 does not detect any DTMF signal during number dialing. The possible causes are as follows:
- A fault occurs on the carrier side. When the user dial a number, the carrier does not send the DTMF signal to the eSpace U1930.
- The DTMF signal sent by the carrier is abnormal in terms of level or frequency and therefore cannot be detected by the eSpace U1930.
Solution
- Use an intra-office phone
to dial a mobile number. When the call is connected, press 0 through 9 in
sequence. The keypad tone can be heard on the intra-office phone.
This check result indicates that the carrier sends the DTMF signal successfully to the eSpace U1930 when keys are pressed.
Whether the DTMF signal of the phone meets the detection standard of the eSpace U1930 needs to be analyzed.
- Capture packets on the
intra-office IP phone and perform the preceding call test again. Stop capturing
packets when the call ends.
The data packets that are obtained contain the DTMF signal of the pressed key.
- Extract a media stream
from the captured packets and analyze the media stream using the audio analysis
software such as the cooledit and coolanalysis.
The following figure shows that the DTMF signal level is just about -29 db.
- On the eSpace U1930, check
the DTMF detection parameter settings in the system.
show mrspara
The return result shows that the detection range of the DTMF signal level is -4 db to -23 db.
The DTMF signal level onsite is -29 db, lower than the minimum threshold. Therefore, the signal failed to be detected.
- Change the minimum
threshold to -36 db and perform the call test again. Digits can be collected
properly.
config modify mrsparas dtmfthrshlevll -36
