SPA 112 - Issue with incoming faxes

[curry0707]

Hello,

I've run into a weird issue with receiving faxes via SPA 112 and wanted to see if anybody has any ideas. We have t.38 enabled with the passthru method set to reinvite. We've done the normal stuff such as disabling ECM on the fax machine and setting the speed to 9600. 

Basically, sending/receiving short faxes usually works fine. But we've run into an issue with receiving longer faxes (10+ pages) where users get the same 10-20 pages over and over again and the fax never completes. This doesn't always happen but it does seem to happen with certain numbers. Was wondering if anybody knew of any settings that might be helpful. We already have - 

Network Jitter: Very high

Jitter Buffer Adjustment: No

Passthru codec: G711u

Disable ECANN: yes

Echo Canc Enable: No

Fax Enable T38: Yes

RTP Packet Size: 0.020

I've also updated the firmware to the latest version. Thanks!

[Philip D'Ath]

We use an auto-provisioning system, so I'm not sure where in the GUI this is, but we had to also set these two additional settings to get it working well.

<Network_Jitter_Level_1_ ua="na">low</Network_Jitter_Level_1_>
<Jitter_Buffer_Adjustment_1_ ua="na">No</Jitter_Buffer_Adjustment_1_>

[Dan Lukes]

I see no way the issue you described can be caused by SPA112.

It's just protocol convertor - it doesn't have store&forward fax mode. So it should not be able to retransmit same page to receiving fax machine - unless such page is retransmitted by caller machine.

Well, there may be something I missed. Can you capture a SIP session including RTP/T.38 stream of affected session ? I care no content of fax, but don't fax sensitive data please.

Can you can turn on debug&syslog of Voice Application and catch them ? I'm curious enough to spend my time to analyze them.

[curry0707]

Thanks, I'll try to reproduce the issue, may take a while to get a capture since it doesn't happen with every fax.

In fact it only seems to happen when receiving faxes from certain fax servers (where they just keep resending the same 10 pages or so over and over). Shorter faxes work fine, and faxes from regular fax machines usually work fine too.

[Dan Lukes]

It's rather rare to have end-to-end T.38 path today. T.38 is converted to classic in-band protocol by a gateway somewhere on the path most of time.A gateway may cause the issue.

Unfortunately, you know no path of particular call and even two calls between same endpoints may not be carried thru same path, so it's hard to debug the issues. 

Well, OK. Capture log, SIP and media packets and attach them here (native .pcap file format is preferred; you need to rename it to .pcap.txt or you will be unable to attach it).