I've been reading about FOIP and there something i dont undrestand. maybe someone can explain to me. A couple of faxing methods im confused about. The pass through method, sending fax data over G711 codec versus Relay method, t30 to t38 conversion Can someone explain to me why the pass through method doesn't require t30 to t38 conversion ( or does it do it?)? i believe the conversion to t38 is so that it can be routed through a packet network and then back to t30 so that the fax machine can understand. why is it that if you use a pass through method, and your still passing through a packet network, you dont need to convert to t38 and t30? hope this makes sense. thanks alot. -------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.digium.com/pipermail/asterisk-users/attachments/20060924/b2eb2c60/attachment.htm
On Sun, Sep 24, 2006 at 01:58:21PM -0700, Christopher Corn wrote:> I've been reading about FOIP and there something i dont undrestand. maybe > someone can explain to me. > > A couple of faxing methods im confused about. > > The pass through method, sending fax data over G711 codec > versus > Relay method, t30 to t38 conversion > > > Can someone explain to me why the pass through method doesn't > require t30 to t38 conversion ( or does it do it?)? i believe > the conversion to t38 is so that it can be routed through a > packet network and then back to t30 so that the fax machine can > understand. why is it that if you use a pass through method, and > your still passing through a packet network, you dont need to > convert to t38 and t30?I believe the proper answer to your question is this: Fax and modem tones will not be passed properly by some codecs because they're optimized for the frequency patterns of human voices -- and because those tones were themselves optimized for a traditional analog or DS-0 PCM channel. Since G.711 *is* an uncompressed DS-0, that's why you can pass fax tones through it, without any help from spoofing protocols like t.38. Cheers, -- jra -- Jay R. Ashworth jra@baylink.com Designer Baylink RFC 2100 Ashworth & Associates The Things I Think '87 e24 St Petersburg FL USA http://baylink.pitas.com +1 727 647 1274 "That's women for you; you divorce them, and 10 years later, they stop having sex with you." -- Jennifer Crusie; _Fast_Women_
Christopher Corn wrote:> I've been reading about FOIP and there something i dont undrestand. > maybe someone can explain to me. > > A couple of faxing methods im confused about. > > The pass through method, sending fax data over G711 codec > versus > Relay method, t30 to t38 conversion > > Can someone explain to me why the pass through method doesn't require > t30 to t38 conversion ( or does it do it?)? i believe the conversion > to t38 is so that it can be routed through a packet network and then > back to t30 so that the fax machine can understand. why is it that if > you use a pass through method, and your still passing through a packet > network, you dont need to convert to t38 and t30? > > hope this makes sense. thanks alot.See http://www.soft-switch.org/foip.html Steve