Date: Sat, 9 Dec 1995 19:21:00 +0100 (MET) From: grog@lemis.de (Greg Lehey) To: chuckr@glue.umd.edu (Chuck Robey) Cc: hackers@freebsd.org (FreeBSD Hackers) Subject: Re: Who's working on ISDN? Message-ID: <199512091821.TAA02565@allegro.lemis.de> In-Reply-To: <Pine.SUN.3.91.951209103930.916B-100000@mocha.eng.umd.edu> from "Chuck Robey" at Dec 9, 95 10:45:02 am
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Chuck Robey writes: > >> Basic Rate in the US has a problem that the trunks usually run 64 kb/s >> with inband signalling. As a result, they take one bit per byte of >> the B channels, and you end up with 56 kb/s B channels. I don't think > > I don't completely understand why they have to move the rate all the way > down to 56K from 64K, when the singalling bits only run one frame in 6, > and each card is told when that is. If I'd have designed them, I'd have > used 56K + 8K * 5/6 = 62666. Yes, I always thought that 16 kB/s for a D channel which only handles 2 B channels is excessive (by comparison, primary rate interfaces, which run 30 B channels in Europe or 24 in the US, have a single 64 kb/s D channel). I suspect that this is a transitional business (I believe it has something to do with the design of the 5ESS, but I don't know much about that machine), and since the "high speed" lines of a few years ago were 56 kb/s, it seems reasonable to assume that this is an easy interim kludge. > On the ohter hand, since telcos have been handling DDS a long time, and > it certainly uses clear channel (with NO bits lost) then I guess I must > be missing something somewhere). Hmm. Whether it's clear channel or something else depends on how they handle the network gateways. I'd guess that that's the point here: they *can* build an efficient gateway from 56 kb/s trunks to ISDN B channels if they do it this way. In any case, it's a stated aim of the US telcos to move to DSS1 (like it's a stated aim of Deutsche Telekom, who atypically have got there first). It would be really nice if there were to be the sort of compatibility which would enable me to call any ISDN number in the US and exchange data via DSS1. Greg
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