srini@progress.COM (Srini Parthasarathy) (05/23/91)
I am kind of new to the world of usenet so bear with me ... What is the essential difference between "regular" modems and fax modems ?? Is there any literature out there that I can lay my hands on ?? To put it simply ... If I have a 9600 baud modem can I use it to xmit fax'es ??? If not , why ?? My email address : srini@progress.com My *THANX* in advance !!
tnixon@hayes.uucp (05/23/91)
In article <1991May22.203729.2006@progress.com>, srini@progress.COM (Srini Parthasarathy) writes: > What is the essential difference between "regular" modems and fax modems > ?? Is there any literature out there that I can lay my hands on ?? > > To put it simply ... If I have a 9600 baud modem can I use it to xmit > fax'es ??? If not , why ?? The essential difference is that the modulation schemes are different. Fax devices use CCITT V.21 (in one direction) for negotiation, and CCITT V.27ter, V.29, and V.17 for image transmission. Modems typically use Bell 103, Bell 212, CCITT V.21 (full duplex), V.22, V.22bis, V.23, V.32, and V.32bis. No overlap there! The other major reason why you need special "fax modems" is that fax transmissions are always synchronous (no start and stop bits), and if you're going to run a fax modem off a standard async comm port the modem needs to be able to strip the start and stop bits off the data automatically. Normal data modems don't do this (although the Hayes AutoSync feature does). So, no, you can't use a normal data modem to send faxes, unless you're going through a third-party service like AT&T Mail or CompuServe (in which case THEY provide the fax modem). -- Toby Nixon, Principal Engineer | Voice +1-404-840-9200 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net