gandrews@netcom.COM (Greg Andrews) (05/25/91)
In article <106126@sgi.sgi.com> vjs@rhyolite.wpd.sgi.com (Vernon Schryver) writes: >In article <1991May24.060836.7247@netcom.COM>, gandrews@netcom.COM (Greg Andrews) writes: >> >> Yes, an uncompressed implementation of SLIP will make PEP thrash between >> different sized packets. It's not a "baud" rate switch at all. It's a >> simple matter of packet size. > >I think it really is a "baud change." I understand from Telebit that while >running micropackets they use something like 18.3 baud, but doing big >packets they use about 7 baud. That is, the signal transmitted by the >modem changes either 7+ or 18+ times/second. Of course, the instantaneous >bit rate at the DTE-DCE interface never changes. >(Yes, the old lecture that "buad" != "bps") > Take it from Telebit support technician (me). This is not, repeat NOT a "baud rate" change in any sense of the term. The modems do not alter the baud rate, nor the modulation, on any of the carriers without retraining. Since the symbol rate and carrier structure don't change without a retrain, neither does the raw bit rate between the modems (as reported in the S70 and S72 registers). What you are hearing is primarily the different packet lengths. You are also hearing a difference in the number of carriers used for transmitting. Out of the total number of carriers available to the modem, long packets will use all of them, short packets use half of them, and micro packets use around 1/8th of them. The characteristics of the "hash" will change between the different types of packets because of the different combinations of carriers used. Once again, this is NOT a baud rate change. No carriers send symbols faster or slower than they did previously. The total *number* of symbols sent simultaneously will change as the number of carriers changes, but all of the carriers still send symbols at the same rate. >Vernon Schryver, vjs@sgi.com -- .------------------------------------------------------------------------. | Greg Andrews | UUCP: {apple,amdahl,claris}!netcom!gandrews | | | Internet: gandrews@netcom.COM | `------------------------------------------------------------------------'
root@zswamp.uucp (Geoffrey Welsh) (05/28/91)
In a letter to All, Greg Andrews (gandrews@netcom.COM ) wrote: >What you are hearing is primarily the different packet >lengths. You are also >hearing a difference in the number of carriers used for >transmitting. Out of >the total number of carriers available to the modem, long >packets will use >all of them, short packets use half of them, and micro >packets use around >1/8th of them. The characteristics of the "hash" will >change between the >different types of packets because of the different >combinations of carriers used. Ah, so if a carrier generates a lot of errors, it will simply be used less often to carry data, rather than affecting its physical characteristics? Makes good sense. -- 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