Date: Sat, 10 Jun 1995 23:01:52 -0400 (EDT) From: Chuck Robey <chuckr@Glue.umd.edu> To: "Edward F. Knight" <e.knight@ix.netcom.com> Cc: questions@freebsd.org Subject: Re: 14400 and 28800 baud rates Message-ID: <Pine.SUN.3.91.950610225347.5710A-100000@mocha.eng.umd.edu> In-Reply-To: <199506100421.VAA01529@ix3.ix.netcom.com>
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On Sat, 10 Jun 1995, Edward F. Knight wrote:
> I have 14.4 and 28.8 baud modems. These baud rates are not supported in
> pppd or kermit.
>
> If anyone has succesfully changed the source of these, could you please
> share what needs to be changed.
The rates that the modem actually transfers the data over the telephone
line no longer have anything to do with the rates the modem transfers the
data to your pc. If you think about that, it needs to be that way for 2
reasons:
1) The modem is error correcting, so if errors occur, it has to transfer
data more slowly.
2) The modem uses compression, sometimes actually sending 2-4 times the
amount of data going over the telephone line.
Because of these two things, you should set your data rate, between the
modem and your pc, to some rate greater than the transfer rate. I set my
28.8 KB modem to 38,400 from the pc, but that's because I almost always
transfer data that's already compacted. If you transfer raw data, on a
28.8 modem, well, some people use 115 kb transfer rates.
I'm not losing anything if the modem tries to outspeed my pc, because I
use something called hardware flow control. That means, my data
interface relies on two signals (wires, actually) in the interface,
called CTS and RTS, to act as traffic cops if the data rate gets too high.
Take a look at the sio man page if you are still curious. There are lots
of books on this subject at your bookstore, its worth looking at.
>
> Thanks
> T.K.
>
>
----------------------------+-----------------------------------------------
Chuck Robey | Interests include any kind of voice or data
chuckr@eng.umd.edu | communications topic, C programming, and Unix.
7608 Topton St. |
New Carrollton, MD 20784 | I run Journey2 (Freebsd 2.0) and n3lxx
(301) 459-2316 | (FreeBSD 1.1.5.1) and am I happy!
----------------------------+-----------------------------------------------
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