From owner-freebsd-questions Fri Nov 1 04:56:07 1996 Return-Path: owner-questions Received: (from root@localhost) by freefall.freebsd.org (8.7.5/8.7.3) id EAA27876 for questions-outgoing; Fri, 1 Nov 1996 04:56:07 -0800 (PST) Received: from Campino.Informatik.RWTH-Aachen.DE (campino.Informatik.RWTH-Aachen.DE [137.226.225.2]) by freefall.freebsd.org (8.7.5/8.7.3) with SMTP id EAA27815 for ; Fri, 1 Nov 1996 04:56:02 -0800 (PST) Received: from gilberto.physik.rwth-aachen.de (gilberto.physik.rwth-aachen.de [137.226.31.2]) by Campino.Informatik.RWTH-Aachen.DE (RBI-Z-5/8.6.12) with ESMTP id NAA16630; Fri, 1 Nov 1996 13:56:50 +0100 Received: (from kuku@localhost) by gilberto.physik.rwth-aachen.de (8.6.11/8.6.9) id OAA09714; Fri, 1 Nov 1996 14:04:41 +0100 From: Christoph Kukulies Message-Id: <199611011304.OAA09714@gilberto.physik.rwth-aachen.de> Subject: Re: Any ISDN-BRI cards work under FreeBSD? In-Reply-To: <199611010818.JAA19813@freebie.lemis.de> from Greg Lehey at "Nov 1, 96 09:18:21 am" To: grog@lemis.de (Greg Lehey) Date: Fri, 1 Nov 1996 14:04:40 +0100 (MET) Cc: questions@FreeBSD.ORG Reply-To: Christoph Kukulies X-Mailer: ELM [version 2.4ME+ PL25 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-questions@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk > Terry Lambert writes: > >>>> done it yet. They currently only run single channel connections (you > >>>> can have two different connections to different destinations). The > >>>> theoretical maximum throughput is 8 kB/s (64,000 bps), which is > >>>> somewhat less than the theoretical maximum of the 115.2 kbps lines > >>>> (11.52 kB/s). > >> > >> Why do you divide by 8 in the one case and by 10 in the other? > > > > My guesses: > > > > 8) 8*8k = 64k; conversion is for sync framing > > > > 10) 1 start + 8bits + 1 stop = 10bits; conversion is for > > async framing > > I'm surprised you need to guess. Yes, that's correct. People seem to > have problems understanding this one, so I'll go into a little more > detail: > > Synchronous transmission is block oriented. Various techniques are > used to recognize the beginning and end of the block, and all the data > in a block are sent without any delay between the bits. When > transmitting 8 bit bytes (octets), there's a ratio of 8 bits per > octet, so 64 kbps becomes 8 kB/s. But in HDLC you have bit stuffing (8th bit or nineth?). Doesn't this have to be taken into account? > > Asynchronous transmission is character oriented. Each character > starts with a start bit, then come the data bits, then one or more > stop bits. Nowadays there is only one stop bit, but that expands each > byte to 10 bits. The advantage is that you don't need any specific > timing between characters (thus the term asynchronous), so it's quite > well suited to things like keyboard input. In sync transmission, each > input character would have to be made into a block. The disadvantage > is the significantly lower data rate. > > > A more interesting question might be 64k + 64k = 128k. 128k != 115.2k. > > Yes, this is where we came in. Currently, the driver can't do that. > Somewhere in the back of my head I have a recollection that TCP can do > it, though: you just set up two routes, and it should be able to pass > packets down the route with the shorter output queue. Can anybody > expand on this? > > Of course, 128k != 128k as well if one is sync and the other is > async. 128k sync is 160k async. > > Greg > --Chris Christoph P. U. Kukulies kuku@gil.physik.rwth-aachen.de