[cisco-voip] Question regarding Rightfax Configuration and "Transmission Error"

[Haas, Neal]

Do you use SIP or PRI, we use PRI 99.9% of the time, ATT does not allow T.38 over SIP.

I will likely get a SIP trunk from Comcast or Time Warner in the future, they both do T.38 over SIP. Both say they can do Faxes without issue.

Thank You,

Neal Haas

From: cisco-voip [mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Brian Meade
Sent: Thursday, April 6, 2017 7:09 AM
To: Frank Arrasmith <frank.arrasmith at gmail.com>
Cc: cisco-voip at puck.nether.net
Subject: Re: [cisco-voip] Question regarding Rightfax Configuration and "Transmission Error"

I've had the most luck turning ECM off and running RightFax at only 9600.  Faxes are slower but usually higher quality and less failures.

On Wed, Apr 5, 2017 at 8:06 PM, Frank Arrasmith <frank.arrasmith at gmail.com<mailto:frank.arrasmith at gmail.com>> wrote:
Calling all Rightfax gurus,
   I have the following question regarding the Rightfax configuration and transmission errors.

Background:
My enterprise has CUCM 10.5 with a pretty dialed in Fax/T38 setup over SIP and MGCP gateways.  For the most part, faxing is pretty solid inbound and outbound to and from PSTN GW's, CUBEs, ,analog VG's, and regular fax machines(we have a lot).  We have a SIP trunk connected to Rightfax 10.5 server, which is managed by another group where we have limited access/experience with Rightfax configuration settings.  It took us awhile to get the Rightfax servers with the correct t38 setup because they had only run traditional CAS T1 prior to us, so it was new to everyone, but it is up and stable except for the following issue..
Symptom :
The problem we see with Rightfax is with Transmission errors.  It starts with our internal customers reporting that they do not receive a fax even when the sender receives confirmation.  Upon further review we see that the suspect call is listed as a "Transmission Error" in Rightfax, so the fax never gets delivered to the customers account/mailbox even though the call completes.
Analysis:
Since we are running T38, we can packet capture at the server, and  we see normal fax protocol exchange, except for the suspect calls where we see "RTN" Messages.  My understanding of the T.30 protocol is that when a RTN message is delivered to the sender, that is an indication for the sender to slow down and resend the last page. We actually see in the messages where the RTN message gets sent, and the sender complies with the notice, and sends again at 12000, then call completes as normal with an EOP message and a DCN message.  In these cases,the Rightfax team actually looks at the fax image and may see a bit of blurriness, but perfectly legible text ,even tho its still marked as transmission failure. We have asked them if there is a setting that can be tuned where the RTN does not cause the service to mark the transmission as failure. To this they reply, "It was working fine before when we were on CAS, so it must be on your end."

I understand where there are cases where the RTN message is sent because the call quality is actually terrible, but in those cases, there is usually several RTN messages and the sender will drop down to 4800 or below , and then usually give up and the call will fail.  This type of failure is rare (unless we have a major outage) and in this case the sending fax sees that it failed and will proceed with its normal retries.
Question:
Is this RTN to transmission failure hard coded, or is this a configurable setting?  If this were a regular fax machine, i think this would be a non issue as the receiver would see the crappy page as well as the good copy of that was sent again in their bundle of received pages.
Any insight is greatly appreciated and for anyone just getting into FAX over IP with Cisco, I highly recommend the following book and Cisco Live presentations from these guys from Cisco TAC.

Fax, Modem, and Text for IP Telephony [Book]<https://www.google.com/aclk?sa=l&ai=DChcSEwiXgOn0wY7TAhXJCioKHRVCANoYABAMGgJ0bQ&sig=AOD64_1ddnEIE3WNy8NH5g7yJ-WnrcChJA&ctype=5&q=&ved=0ahUKEwjei-P0wY7TAhUnj1QKHejtCy0QwzwIEg&adurl=>
from Textbooks.com
by David Hanes, Gonzalo Salgueiro





Thanks,
 Frank


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