gandrews@netcom.COM (Greg Andrews) (06/03/91)
In article <147.28486D85@zswamp.uucp> root@zswamp.uucp (Geoffrey Welsh) writes: > > If someone could be bothered to impliment MNP3 and 4 on a Bell 103J modem, >I'm sure that you could get the same relative speed boost at 300 bps. > It's not so much as bothering to do it (after all, the modem designers already did it for the faster modulations, right?), as it is impossible to implement MNP3 or V.42 over a Bell 103J modulation (or V.21). MNP3 and V.42 rely on the modems having a synchronous link through the phone line (otherwise you can't use the HDLC-like framing which allows the stripping of start and stop bits). Bell 103J and V.21 are not synchronous modulations. That wouldn't stop anyone from implementing MNP2 as the base protocol and adding MNP4 header reduction and MNP5 data compression. I believe that's exactly what the software MNP implementations do. >Geoffrey Welsh - Operator, Izot's Swamp BBS (FidoNet 1:221/171) >root@zswamp.uucp or ..uunet!watmath!xenitec!zswamp!root -- .------------------------------------------------------------------------. | Greg Andrews | UUCP: {apple,amdahl,claris}!netcom!gandrews | | | Internet: gandrews@netcom.COM | `------------------------------------------------------------------------'
root@zswamp.uucp (Geoffrey Welsh) (06/03/91)
In a letter to All, Greg Andrews (gandrews@netcom.COM ) wrote: >In article <147.28486D85@zswamp.uucp> root@zswamp.uucp >(Geoffrey Welsh) writes: > > If someone could be bothered to impliment MNP3 and 4 on a Bell 103J modem, >I'm sure that you could get the same relative speed boost at 300 bps. > >It's not so much as bothering to do it (after all, the modem >designers >already did it for the faster modulations, right?), as it >is impossible >to implement MNP3 or V.42 over a Bell 103J modulation (or >V.21). >MNP3 and V.42 rely on the modems having a synchronous link >through the phone >line (otherwise you can't use the HDLC-like framing which >allows the stripping >of start and stop bits). Bell 103J and V.21 are not >synchronous modulations. Then perhaps I misunderstand MNP3... what's to stop a modem manufacturer from operating an FSK carrier (based on Bell 103J specs) at a carefully fixed bit rate and sending the bit patterns required over that link? As I understand it, HDLC framing uses an encoding on the bits to prevent long streams of zero bits from appearing in the normal data stream and uses violations of that rule as sync signals... can this not be done over FSK lines?!? Is there some form of subtle out-of-band signalling available under CCITT V.22[bis]? >That wouldn't stop anyone from implementing MNP2 as the base >protocol and >adding MNP4 header reduction and MNP5 data compression. I >believe that's exactly what the software MNP implementations do. That's all that I've seen so far. -- Geoffrey Welsh - Operator, Izot's Swamp BBS (FidoNet 1:221/171) root@zswamp.uucp or ..uunet!watmath!xenitec!zswamp!root 602-66 Mooregate Crescent, Kitchener, ON, N2M 5E6 Canada (519)741-9553 "He who claims to know everything can't possibly know much" -me