Intermittent faxing failures

Unanswered Question
Jan 19th, 2010

Hello Everyone,

We have approx 15 or so fax machines connected to a VG-248>call manager>(mgcp)gateway>pstn.

A group of users with high visibility within our organization has been sending complaints that a high number of outbound fax transmissions fail to various international numbers. I have monitored several of these “failed” attempts and notice that when the destination number answers the call, our end does not proceed to transmit. (almost as if that “handshake” is taking place). Though intermittent, I have been asked to confirm that our “setup” is configured optimally for faxing internationally and that we are configured to "recognize the different kinds of tones" (if that makes any sense). I am looking to the forum for any help about where to even begin this type of troubleshooting. This is a tall order for me, as I am not a voice expert and not even quite sure where to begin looking …the gateway config? VG248 config? The fax machines themselves? Is there any trace of these calls I can gather that will detail what is (or isn’t happening)? I’m grateful for any help you can offer.

Many thanks,

Kelly

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silversnc Tue, 01/19/2010 - 12:24

Ahh the bane of my existence with VoIP... Faxing solutions...

So with about 5 VG224's on our campus I have encountered numerous issues with faxes.. as of late I have been able to narrow it down quite a bit but I don't fully have a definite answer..

In my experience with the delay in handshake and then a dropped call these steps have helped...

1. There are a few settings you can check on your faxes....

    If you can lower the speed on your fax it tends to help drop it down to 9600 bps and turn of ECM or Error Correction Mode.

          ECM is implemented on the Gateway already and tends to interfere with the faxing and how the gateway interprets the analog signal if you do it on the fax as well..

2.It is possible it is on the customer side with the high speed faxes 33.6kbps I have noticed that sometimes it takes 2-3 retries before it actually accepts the fax, (not sure if it is the fax trying the next highest speed so if it drops from 33.6 to 14.4 to 9.6 which is optimal for VoIP sending)

On a side note, be ready to start troubleshooting customer side faxes for their faxes not being received as well.. I have already encountered 2 offices that luckily were fairly local and i had to visit their offices... Basically they needed to dumb down their fax machines to the 9600bps and turn of ECM and faxing worked flawlessly...

I will say that not to many of our users fax out of the country so I cannot speak to that issue of compatibility..

I'm currently trying to shoot this up the Cisco engineer line to find out why faxing is such a big issue and its extremely flaky and incompatible with so many fax machines that are out there... so if I find out anything I will pass it on...

If anyone has any more experience or ideas on how to get some of these issues resolved please let me know.

Thanks

Nathan

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