Network topology: MA5620E-MGC (from vendor A)-TG (from vendor A)-PSTN
Symptom: The voice user is connected to the MA5620E, the voice service test is normal, but the fax service is abnormal all the time.
1. Check the negotiation parameters of both devices. It is found that the fax mode on both of them is set as the T.30 fax mode.
2. Test the network. It is found that none of packet loss, loop, and long delay occurs in the network.
3. The test result shows that the fax service between the users of the same MA5620E is normal, the fax service between the users of different MA5620Es that are connected to the same MGC is normal, the fax service between the users of the PON devices from different vendors but connected to the same MGC is normal; the fax service receipt/sending of the PSTN is abnormal.
4. Outgoing fax service and transmission/receipt of fax service data to/from PSTN users require the cooperation of the TG, so it can be determined that the peer TG is faulty. The analysis of the packets captured shows that during the RTP negotiation of outgoing fax service the peer TG (from vendor A) always transmits the RTP traffic “payload type:unknown(101)" to the MA5620E. As a result, the MA5620E fails in decoding and therefore the fax service cannot be transmitted or received normally.
5. On the TG (from vendor A), change the setting of the parameter “ V.152 switch need to be adjusted during the cooperation with the devices of other vendors for Internet access and fax through dialup”. Perform a test after parameter adjustment. It is found that no error packet is reported.
6. After the data setting of the peer TG is changed, test the outgoing and incoming fax services. It is found that both outgoing and incoming fax services of the PSTN are normal.
1. The fax service data and negotiation parameters are incorrect.
2. The network is unstable, a large number of packets are lost, the delay is long, or a loop exists.3. The interoperated device is faulty.
If the parameter setting of the TG (from vendor A) is not changed, the modem cannot be implemented either. The cause is the same as that of the fax service problem.