This Wikipedia article breaks it down quite well. http://en.wikipedia.org/wiki/T.38
Tonight I'm not finding any articles that describes the issues with ECM, although I do see some that talk about using it if QOS is set up on the network. ? Sorry, I can't explain any further. I would like to learn more about this subject if others have experience with it. One of the development engineers at Nortel may be able to find some whitepapers, etc. written about the subject on the internal network, as it is a well understood issue on other hardware platforms. -----Original Message----- From: Keith Gearty [mailto:[email protected]] Sent: Friday, June 12, 2009 12:51 AM To: [email protected] Cc: [email protected] Subject: Re: [sipx-users] fax compatibility list? Sorry to butt in here. I know a bit about VoIP, but not much about Fax over IP. I'd be curious to know why Error Correction (ECO ??) doesn't work when the data stream is routed via IP. I assume we're talking about POTS fax machines connected via an FXS->IP gateway? Or are these actual IP fax machines? Regards, Keith. Matt Keys wrote: > Thanks for the information Todd and Jan. I'll pay closer attention to > the fax machine itself. > > The successful test was performed using a SPA-2102 running version > 3.3.6 firmware, hardware version 1.2.5a. The fax models were a > Panasonic KX-FL511 and a Ricoh Aficio 3030 on the other--Both are G3. > > The failed test was using AudioCodes MP-112 running version 5 > firmware. I used a Brother MFC-8220 on one end and the same Panasonic > KX-FL511 on the other. I also tried the HP test fax number I mentioned > earlier--I'm not sure what they use on their end. Outbound I could > hear the fax tone for about 2 seconds and then it went silent. Inbound > (Panasonic to Brother) the fax went through. > > > -----Original Message----- > From: [email protected] on behalf of Todd Hodgen > Sent: Thu 6/11/2009 3:00 AM > To: 'Jan Schumacher'; [email protected] > Subject: Re: [sipx-users] fax compatibility list? > > Sorry, Fat fingered that one. G3. I've had instances with some fax > machines that receive a call from a like machine and they determine that > they are Super G3 compatible, they turn ECO back on when it is turned off. > I think it's a Panasonic if I'm not mistaken. You think everything is > working fine, and then intermittently, you get faxes that don't work. You > scramble around playing with gateways, etc. to find it was a fax > machine all > along. It's that Super G3 tone that is being manhandled by one ITSP to > improve their fax service over their IP network. It's a real problem for > the ITSP's, although many don't admit it, while others openly say it's a > problem. > > I've not ran into T.38 redundancy. It's been a while since I read the > spec's on T.38, but from what I remember, T.38 since it has no error > correction, transmits each packet multiple times as its form of > ensuring the > data gets to the other side. If my memory serves me, what I remember > reading is that the standard doesn't say how many times to transmit > it, that > it's up to the sender to determine how many times to transmit the data. I > did a quick google on T.38 redundancy and Cisco was saying in their > configuration that it determines the number of times the data is > transmitted. It didn't go into great detail, but lead me to believe that > they allow theirs to be configurable maybe? > > I'm by no means an expert on this subject, I just have a few more grey > hairs > from it having fought issues from it with some larger customers. > > Sometimes it's to easy to point a finger at something we don't understand, > when the real issue is really another component on the network. I'm only > suggesting people not ignore that their fax issues could actually be > the fax > machines and their inability to play within the constrictions of > T.38. And, > it's a really easy thing to check out. One big key, if you get one > page and > then it drops each time, check ECO. > > -----Original Message----- > From: Jan Schumacher [mailto:[email protected]] > Sent: Wednesday, June 10, 2009 11:36 PM > To: [email protected]; [email protected] > Subject: Re: [sipx-users] fax compatibility list? > > Hi Todd, > > what did you mean with G5 fax machine? Is it a T.38 IP fax machine? > Is it better to turn off the T.38 redundancy too? > > Jan > > 2009/6/11 Todd Hodgen <[email protected]>: > > Are you sure the issue is with the Gateway itself and not the fax > machines. > > It's important on the faxes to turn off Error Correction. And, it gets > > trickey, because some machines allow you to turn them off, some require > the > > manufacturer to turn them off, and some turn back on by themselves when > they > > detect a G5 fax machine. Error Correction must be turned off for Faxing > to > > work in an IP network. I learned this lesson the hard way with some > large > > Nortel CS1000 implementations. Problem wasn't the switch, but the fax > > machines on the ends, and the T.38 protocol itself. > > > > I know of at least one ITSP's that's even beginning to tweak their > network > > now to ensure error correction is stripped off of their network entirely > to > > improve fax capabilities. > > > > Voipfrustration.com is a sight that has instructions for turning off > Error > > Correction on different Fax Machines, it can be helpful when things are > > coming together. > > > > > > > > -----Original Message----- > > From: [email protected] > > [mailto:[email protected]] On Behalf Of Matt Keys > > Sent: Wednesday, June 10, 2009 9:42 PM > > To: [email protected] > > Subject: [sipx-users] fax compatibility list? > > > > Is there a list of sipxecs tested/certified ATAs that work for faxing? I > > was able to get a SPA-2102 to send/receive yesterday. Tests using a > > AudioCodes MP-112 (version 5 firmware) have failed. > > > > FYI - I just discovered HP has a very handy tool available. Call > > 1-888-hpfaxme (1-888-473-2963) and it will receive your test fax and > > send it back to you. See > > > http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00259105&lc=en&dlc=&cc= > <http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00259105&lc=en&dlc=&cc => > > us&product=424230 . > > > > > > _______________________________________________ > > sipx-users mailing list [email protected] > > List Archive: http://list.sipfoundry.org/archive/sipx-users > > Unsubscribe: http://list.sipfoundry.org/mailman/listinfo/sipx-users > > sipXecs IP PBX -- http://www.sipfoundry.org/ > > > > _______________________________________________ > > sipx-users mailing list [email protected] > > List Archive: http://list.sipfoundry.org/archive/sipx-users > > Unsubscribe: http://list.sipfoundry.org/mailman/listinfo/sipx-users > > sipXecs IP PBX -- http://www.sipfoundry.org/ > > > > _______________________________________________ > sipx-users mailing list [email protected] > List Archive: http://list.sipfoundry.org/archive/sipx-users > Unsubscribe: http://list.sipfoundry.org/mailman/listinfo/sipx-users > sipXecs IP PBX -- http://www.sipfoundry.org/ > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 8.5.339 / Virus Database: 270.12.50/2150 - Release Date: > 06/10/09 05:52:00 > >------------------------------------------------------------------------ > >_______________________________________________ >sipx-users mailing list [email protected] >List Archive: http://list.sipfoundry.org/archive/sipx-users >Unsubscribe: http://list.sipfoundry.org/mailman/listinfo/sipx-users >sipXecs IP PBX -- http://www.sipfoundry.org/ > >------------------------------------------------------------------------ > > >No virus found in this incoming message. >Checked by AVG - www.avg.com >Version: 8.5.364 / Virus Database: 270.12.62/2168 - Release Date: 06/10/09 18:30:00 > > > _______________________________________________ sipx-users mailing list [email protected] List Archive: http://list.sipfoundry.org/archive/sipx-users Unsubscribe: http://list.sipfoundry.org/mailman/listinfo/sipx-users sipXecs IP PBX -- http://www.sipfoundry.org/
