tnixon@uunet.uu.net (Toby Nixon) (03/10/91)
I received notice this morning via AT&T Mail from Dick Brandt, vice chairman of CCITT Study Group XVII, that V.17 and V.32bis were approved and are now formally adopted as CCITT Recommendations. He did not report the actually vote tally, but I assume that it was unanimous. V.17 is the new modulation scheme that provides 12000 and 14400 bps trellis-coded modulation for Group 3 facsimile. CCITT Recommendations T.4 and T.30, which define Group 3 fax, have also been amended to reference V.17 and provide for negotiation of its use (and those amendments have been adopted as well). V.17 also adds trellis-coded modulation at 7200 and 9600; these speeds are also provided in Group 3 fax by V.29 modulation but without trellis coding. V.17 should thus allow these speeds to be used on somewhat worse lines than was previously possible. V.32bis is an extension of CCITT V.32 which adds speeds of 7200, 12000, and 14400bps, full-duplex on two-wire dial-up or leased lines. V.32bis also adds a "rapid rate renegotiation" feature which allows the modems, by mutual agreement, to shift data rates up or down through a simple signalling process that takes about 1/10th of a second; V.32 requires a full retrain, which takes from five to ten seconds, in order to change speeds. 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
peter@taronga.hackercorp.com (Peter da Silva) (03/11/91)
hayes!tnixon@uunet.uu.net (Toby Nixon) writes: > V.17 is the new modulation scheme that provides 12000 and 14400 bps > trellis-coded modulation for Group 3 facsimile. Any relation to Telebit's proprietary "PEP" protocol? peter@taronga.uucp.ferranti.com
tnixon@uunet.uu.net (Toby Nixon) (03/11/91)
In article <telecom11.196.3@eecs.nwu.edu>, peter@taronga.hackercorp. com (Peter da Silva) writes: >> V.17 is the new modulation scheme that provides 12000 and 14400 bps >> trellis-coded modulation for Group 3 facsimile. > Any relation to Telebit's proprietary "PEP" protocol? We should probably move this to comp.dcom.modems, but anyway... No, V.17 is not related to PEP at all. In fact, V.17 is _really_ a half-duplex version of V.32bis. The modulation scheme (constellation, coding, etc.) of V.17 is identical to V.32bis at 7200, 9600, 12000, and 14400. But because it is an application-specific modulation standard intended specifically for Group 3 fax, it is half-duplex. It includes a fast turnaround capability, talker echo protection, and "turn off" sequence, which apply to half-duplex modems only. V.17 also does NOT include the "rate signalling" bits of V.32bis, but instead depends on Group 3 negotiation procedures (T.30) to indicate data rate. 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
ccplumb@rose.uwaterloo.ca (Colin Plumb) (03/15/91)
peter@taronga.hackercorp.com (Peter da Silva) wrote: > hayes!tnixon@uunet.uu.net (Toby Nixon) writes: >> V.17 is the new modulation scheme that provides 12000 and 14400 bps >> trellis-coded modulation for Group 3 facsimile. > Any relation to Telebit's proprietary "PEP" protocol? Not the slightest. V.17 looks a lot like V.32bis, which looks nothing like PEP. The resemblance is as close as Latin is to Japanese. Colin