Symptom
A fax machine uses a China Mobile number. The fax machine can exchange faxes properly with China Mobile numbers. The fax machine can receive faxes from China Telecom numbers, but cannot send faxes to China Telecom numbers.
Possible Cause
The possible causes are as follows:
- Fax signals replied by China Telecom recipients cannot be properly detected.
- Fax media negotiation fails.
Solution
- Compare the fax packets exchanged with a China Mobile number and a China Telecom number onsite. When the fax machine sends a fax to the IMS China Mobile number, the packets contain the modem media attribute. During media negotiation, the China Mobile number returns the modem media attribute. However, when the fax machine sends a fax to the China Telecom number, the China Telecom number returns the fax media attribute. The SoftCo regards that the two ends fail in media negotiation, and sends code 500 to the fax machine.
- If the IAD detects signals sent from the timer within 10 seconds, the IAD regards the signals as fax signals; otherwise, the IAD regards the signals as modem signals. Run the config system foip t38 v21timerlen 25 command to change the duration for detecting fax signals to 25 seconds. The fault is rectified.
- If the fault persists, contact your service provider for assistance.
