[from AsterFax] SpanDSP error codes ( useful if you are about to organize faxing from asterisk or other voip )
http://asterfax.sourceforge.net/SpanDSP.html SpanDSP provides the core functionallity within Asterisk for sending and recieving faxes. spandsp is a library which provides many of the DSP functions needed for telephony. It is designed to be independent of the telephony platform itself. http://www.soft-switch.org/spandsp_faq/