Hi all, I built a mod_fax setup which is working well. Hats off to the authors for the module. I receive faxes regularly without issue. I can also send faxes, but seem to have a higher failure rate, especially with faxes over 10 pages, usually with error 21: No response after sending a page. I know fax-over-IP can be dicey sometimes (don't know if T.38 would help but see that mod_fax doesn't support yet anyway), but here's my question: Are there any best practices when using mod_fax? Codecs to use or avoid, jitter settings, OS tuning, etc? Things that you guys have learned through live use. Sorry if its a newbie question but I've read through the documentation and wiki but haven't seen much in this. About the system: Dedicated hosted server, Debian 5, Freeswitch 1.0.4. Nothing else running on the system. Any thoughts or lessons learned would be greatly appreciated. Cheers, Rob Forman
Hi all, Made some progress on the success rate of faxes and question about mod_fax default settings that might help others just getting starting. ECM is turned on by default- which proved problematic, at least for my setup. ECM, if I understand correctly, is the Error Correction Mode which allows fax machines to detect errors in small blocks of data on a page (via check sums) and request that just those blocks be re- transmitted (http://en.wikipedia.org/wiki/Error_correction_mode). Unfortunately, I was seeing a build up of resend requests in the debug logs which eventually, on 10+ page faxes, exceeded the limit and caused the fax to fail. Disabling ECM prevented this failure, though, as I understand it, possibly at the expense of quality. Certain blocks could have errors that aren't corrected. I haven't seen any visible loss in quality though and now am transmitting and receiving with a very good rate of success. I guess the next question is why there were so many resend requests. Is that just part of the fax-over-ip territory? Or is there more than can be tuned? Thoughts anyone? Cheers, Rob On Sep 8, 2009, at 10:29 AM, Rob Forman wrote:
Hi all,
I built a mod_fax setup which is working well. Hats off to the authors for the module. I receive faxes regularly without issue. I can also send faxes, but seem to have a higher failure rate, especially with faxes over 10 pages, usually with error 21: No response after sending a page.
I know fax-over-IP can be dicey sometimes (don't know if T.38 would help but see that mod_fax doesn't support yet anyway), but here's my question:
Are there any best practices when using mod_fax? Codecs to use or avoid, jitter settings, OS tuning, etc? Things that you guys have learned through live use. Sorry if its a newbie question but I've read through the documentation and wiki but haven't seen much in this.
About the system: Dedicated hosted server, Debian 5, Freeswitch 1.0.4. Nothing else running on the system.
Any thoughts or lessons learned would be greatly appreciated.
Cheers, Rob Forman
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Rob Forman