Not able to receive faxes

[lbschmitz]

Hi All,

I'm having a hard time to setup the Fax Server at my 3CX application. According to the tutorials should be really straight forward however I'm not able to figure out. Got the logs and when I call the number I get the Fax beep but any attempt to delivery the message fails.

Every message creates a xml file where the error line is:
<RCV_ERROR>Call was either not from a fax machine, or else fax handshaking failed</RCV_ERROR>

I'm not sure where is the gap. The Media Server logs show: No RTP packets were received:remoteAddr=127.0.0.1:10002,extAddr=0.0.0.0:0,localAddr=127.0.0.1:7292

My VoIP provider supports T38 and under DID I have "Send fax to: email of extension 8888 ( Fax Extension)

I have the extension number email and authentication password. I can see that the server is being registered under the logs.

18:07:30.651|2868|(0):FAXServer,
(User nai 1) SSC Evt (Register): Receive FOIP__SIP_REGISTER_RQ
18:07:30.652|3280|FaxServer.cpp(213):FAXServer, MainServiceProc::Run(), Service started


Do you guys have any direction where I'm missing here ?

Thank you in advance.

 

[lneblett]

What version and edition of 3CX are you working with?

 

[lbschmitz]

Hi lneblett

Thank you for answering.

I'm using version 12.5 and product is 3CX Phone Sysmte Professional Edition.

I've looked at the logs and tried to understand why the fax is not being received without success.

Any direction you could point ?

Thank you in advance.

 

[bardissi]

Are you using SIP trunks?

Does your sip trunk provider use t.38?

Have you asked them to check on their side to see if there is an issue?

 

[lneblett]

A few things -

You may need to check with the provider to insure that the trunk/number you have associated to the fax server is indeed provisioned for t38. It could be that while they support t38, it has to be specifically requested.

You may want to turn off the Windows or 3rd party firewall on the 3CX system and test again.

Insure that the fax server service is running and that the fax service status shows green.

For whatever reason, it appears that the media server for the fax server never saw the packets and subsequently would/will hang up. It will not support other codecs like g711 pass-through.

A wireshark capture of a call may be needed to see what is actually being sent.

 

[lbschmitz]

Hi Ineblett,

Thank you so much for the directions.

I'm in contact with my provider Flowroute, to make sure the trunk is provisioned for t38. I've tested and captured the traffic with wireshark start to seeing some tutorials of analysing the results. I also attached the .pcapng and sent to Flowroute support so they can have a look and see if it's something at their end.

Under the wireshark I can see the same message at the logs "Unknow RTP version 0" as I'm getting into the media center: No RTP packets were

I've added the wireshark file here as well if you want to take a look I'd would be really appreciated.

Thank you for your help!

 

[lneblett]

Did not see an attachment.

 

[lbschmitz]

I didn't see that the .pcapng wasn't allowed.

It's attachend with a .zip file

 

[lneblett]

I took a look at the capture. A couple of things come to mind:

if you look at the flow the left most IP address is that of the provider, the center is 3CX and the right most is that of the media server that the provider is using to send the RTP packets. The invites look to be correct, although I am uncertain why the use of the 184.x.x.x address. This appears to be a public IP and for reference, you should take the steps necessary to mask some of the details as it otherwise reveals a prime candidate for hacking. A simple look-up shows the IP to have been issued by Shaw in Canada. Also it can be pinged.

Can you explain how you have the system configured? Is it indeed exposed directly to the internet or is it behind a NAT? Where was the wireshark capture taken.....on the 3CX machine itself or via a port mirror of a WAN port from the router?

You will note that the flow only shows one-way streams from your 3CX system to the media server. IT is trying, but the system is not seeing any return.

If you will look at my flow (faxflow 2) you will note the internal IP for the 3cx system and you will see that the flow is bi-directional between 3CX and the provider's media server.


WHat I also see is that in the SDP to the provider, the system indicated it wanted to use t38 on port 9092: Media Port: 9092. They ack'ed the request and indicated that they wanted you to communicate with them on port 13502. 3CX is sending out on 13502 as requested, but they appear to be trying to respond to you on port 9090:
Destination port: websm (9090)

As 3CX is expecting to see the return om 9092 and it appears that the response is coming in on 9090, that is the reason for not receiving the fax and getting no RTP packets.

So the question is whether the provider is in error or if a router is doing port translation or your system set-up is causing some issue.