Date: Fri, 1 Nov 1996 09:28:40 +0100 (MET) From: Greg Lehey <grog@lemis.de> To: joerg_wunsch@uriah.heep.sax.de Cc: FreeBSD-current@FreeBSD.ORG (FreeBSD current users), isdn@muc.ditec.de (FreeBSD ISDN Distribution List) Subject: Re: Any ISDN-BRI cards work under FreeBSD? Message-ID: <199611010828.JAA19837@freebie.lemis.de> In-Reply-To: <199610311858.TAA16867@uriah.heep.sax.de> from J Wunsch at "Oct 31, 96 07:58:39 pm"
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J Wunsch writes: > As Christoph Kukulies wrote: > >>>> In Germany and other parts of Europe, the Teles S0 and compatible >>>> boards are supported. They *should* work in the US, though nobody's >> >> I'd really be surprised if these cards would work at 56Kb/s and >> if they's connect physically. > > The 56/64 is only one frame bit that's being used differently (not for > the data channels in the US). AFAIK, the raw frames are similar, and > the Teles cards are probably dumb enough :) to not see the difference > anyway. The Teles cards are almost certainly dumb enough. The problem is in the software, which is almost certainly too dumb to handle the problem. I'm not too sure exactly how the data are framed in 56 kb/s simulated ISDN. The one missing bit is used to carry the D channel across the trunks, but I don't know how they map it to the local loop. I think the local loop still runs at 192 kb/s (2x64 kb/s B channels, 16 kb/s D channel, 48 kb/s timing), but only 7 bits of every 8 on the B channel are significant. You'd have to extract these bits and put them back together as a coherent data block, which would take up quite a bit of CPU time. If I'm wrong, and the D channel is still in the 8th bit, you'll have even more work to do. I would guess that the Teles board will still function as long as the loop runs at 192 kb/s. The good news, however, is that 56 kb/s is not the only game in town. It was only ever intended as an interim measure, and many areas supply 64 kb/s. Could somebody in the US please comment? Greg
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