Date: Wed, 3 Sep 1997 17:54:18 +0930 From: Greg Lehey <grog@lemis.com> To: Mike Smith <mike@smith.net.au> Cc: FreeBSD Chat <chat@FreeBSD.ORG> Subject: Re: Anyway to get connect speed with usermode ppp/tun0 device? Message-ID: <19970903175417.21095@lemis.com> In-Reply-To: <199709030806.RAA00241@word.smith.net.au>; from Mike Smith on Wed, Sep 03, 1997 at 05:36:51PM %2B0930 References: <19970903163957.09017@lemis.com> <199709030806.RAA00241@word.smith.net.au>
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On Wed, Sep 03, 1997 at 05:36:51PM +0930, Mike Smith wrote: >> (moved to chat) >> >> On Wed, Sep 03, 1997 at 04:29:44PM +0930, Mike Smith wrote: >>>> >>>>> The speed is specified as 'baud'; in fact, it's bit per second. >>> >>> It is correct to specify the speed as "baud" in conjunction with a >>> single-wire serial interface. >> >> I suppose you mean a two-wire interface. > > No. A two wire interface can transport four values per baud. That depends how it's modulated. >> Sure, you can use the term >> baud if that's the speed talking about. Here we're talking about a >> 2400 baud interface. It's transferring 38,400 bits per second. > > Not by any definition I can comprehend. You have a single wire serial > interface, clocked at 38,400 transitions per second. Look down the wire. > That is 38,400 baud no matter which way you look at it. To achieve > 38,400 bps at 2400 baud you need a signalling mechanism with 65536 > possible values, or 16 bits of significance. This puts you in the > high-end trellis-encoding market, certainly not on good ol' EIA-232. In the context we're talking about, nobody's talking about good old RS-232. We're talking about a modem link. The bauds only make sense when they're not bits per second; otherwise they're just obfuscation. >> OK, you might say "this interface is between the serial interface and >> the modem". And yes, over this interface the speed is 38,400 baud as >> well as 38,400 bps. But that's \fIvery\fP misleading, and there's no >> need for it. > > I don't understand. stty can only report on the configuration of the > serial port, and it does that correctly. But misleadingly. And for no good reason. > It has no way of knowing what the modem thinks its doing; as I have > already pointed out it is impossible to know what the modem is > "really" doing at any point in time anyway. You said that you didn't know a way to extract the information. That's not quite the same thing. If I could dig my modem docco out of one of this maze of twisted boxes, all alike, I could check on that, but wasn't there an S register that contains this information? Greg
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