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