CHARLIE@UMVMA.BITNET (Charlie Turner) (03/12/91)
I have a few Fax modem questions and didn't know where else to turn since my listserv lists (bitnet listserv master list) didn't show any fax lists. The terms group-2, group-3, and V.29 are all, I believe, CCITT standards. Presumably then a group-3 fax modem sends and receives whatever that data format is using V.29 modulation. Is this true? Are the scan resolutions 203x98 lines/in (or 203x196 lines/in) part of the group-3 definition? I have seen group-2 called "3-minute fax" and group-3 called "sub- minute fax". Is it correct to assume from this that group-3 is faster than group-2? Our office stand alone fax machine has polling operation, remote terminal IDs (RTI), polling permission numbers (PPN), and transmit terminal IDs (TTI). Are these things part of the group-3 standard or are they specific to a particular manufacturer's product? The software that operates a fax modem board may send and receive data files in some standard graphics-type format. If this is true then what format is it? Any comments will be appreciated. Thanks.
tnixon@hayes.uucp (03/13/91)
In article <9103122109.AA22187@ucbvax.Berkeley.EDU>, CHARLIE@UMVMA.BITNET (Charlie Turner) writes: > I have a few Fax modem questions and didn't know where else to turn > since my listserv lists (bitnet listserv master list) didn't show > any fax lists. There is a comp.dcom.fax newsgroup, opened a few months ago. But I'll answer these questions for you here, anyway. > The terms group-2, group-3, and V.29 are all, I believe, CCITT > standards. Presumably then a group-3 fax modem sends and receives > whatever that data format is using V.29 modulation. Is this true? Group 3 uses five different modulation schemes: V.21 (predominantly) or V.27ter for negotiation of parameters between the machines, then V.27ter (2400 or 4800bps), V.29 (7200 or 9600 bps), V.33 (12000 or 14400 bps), and V.17 (7200, 9600, 12000, and 14400 bps, trellis coded) for image transfer. > Are > the scan resolutions 203x98 lines/in (or 203x196 lines/in) part of the > group-3 definition? Yes. The encoding and compression is defined in CCITT Recommendation T.4. The negotiation of options is defined in CCITT Recommendation T.30. > I have seen group-2 called "3-minute fax" and group-3 called "sub- > minute fax". Is it correct to assume from this that group-3 is > faster than group-2? Yes. Group 2 uses a different modulation scheme and compression technique that is considerably slower. The VAST majority of fax machines in the world are Group 3 machines. > Our office stand alone fax machine has polling operation, remote > terminal IDs (RTI), polling permission numbers (PPN), and transmit > terminal IDs (TTI). Are these things part of the group-3 standard or are > they specific to a particular manufacturer's product? Polling and terminal identification are standard Group 3 functions defined in T.30. "Permission", that is, checking to see if a certain remote machine is allowed to poll, is a manufacturer-specific feature. > The software that operates a fax modem board may send and receive > data files in some standard graphics-type format. If this is true > then what format is it? The only formats that can be actually transferred across the phone line are those defined in T.4. However, software can translate from various PC file formats (text, PostScript, PCX, GIF, TIFF, etc.) to T.4 format. The translation supported are entirely up to the implementor of the software. -- 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