Step 1 Perform mirror packet capture on the switch, and use the Wireshark to capture packets on the service port of the U1960 when using different fax numbers to send faxes. Record the packet capture result for each successful or failed fax separately.
Step 2 Analyze the packets captured by the Wireshark to find the differences between packets for successful and failed faxes.
It is found that faxes fail in the following situations:
When fax training starts, the training confirmation tone returned by the peer fax machine overlaps the next training tone sent by the local fax machine. As a result, the local fax machine cannot recognize the confirmation tone, and the fax fails.
The following figure shows the correct training tone.
After the local fax machine sends the EOP message when fax training ends, the peer fax machine returns the MCF message, which overlaps the DCN message sent by the local fax machine. As a result, the local fax machine cannot recognize the MCF message, and the fax fails.
The following figure shows the correct fax ending tone.
Based on the preceding packet analysis, it is preliminarily confirmed that the U1960 and IAD run properly.
Step 3 Provide the preceding analysis result to the customer. The customer decides to contact the E1 line provider to check the network delay cause.