From owner-freebsd-isdn Mon May 24 9:57:54 1999 Delivered-To: freebsd-isdn@freebsd.org Received: from ixori.demon.nl (ixori.demon.nl [195.11.248.5]) by hub.freebsd.org (Postfix) with ESMTP id B6DA214CF5; Mon, 24 May 1999 09:57:07 -0700 (PDT) (envelope-from bart@ixori.demon.nl) Received: from localhost.ixori.demon.nl (localhost.ixori.demon.nl [127.0.0.1]) by ixori.demon.nl (8.9.3/8.9.1) with ESMTP id TAA01806; Mon, 24 May 1999 19:01:07 +0200 (CEST) (envelope-from bart@ixori.demon.nl) Date: Mon, 24 May 1999 19:01:06 +0200 (CEST) From: Bart van Leeuwen To: Tom Cc: Dag-Erling Smorgrav , isdn@freebsd.org, blitz@pdq.net, stable@freebsd.org Subject: Re: ISDN Terminal adapter no work In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-isdn@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org On Mon, 24 May 1999, Tom wrote: > On 24 May 1999, Dag-Erling Smorgrav wrote: > > > "Craig Harding" writes: > > > Most TA's act just like very fast modems. > > > > "very" is perhaps not the right word, since an single ISDN channel is > > less than twice as fast as a 33k6 modem. > > Nope. > > First of all, most everyone gets 2B+D ISDN (2 x 64K) anyhow, in fact > 1B+D (64k) isn't available in most areas of the world. > > Second, ISDN is sync, but modems are async. Now some people use various > async emulation protocols over ISDN (like V.120), but that is a complete > waste, especially if all you are doing is PPP. > > Here is what is looks like: > > 64k ISDN channel: 64000 / 8 = 8000 bytes/sec > 2 x 33.6 modem: 67200 / 10 = 6720 bytes/sec > Uusually async modems also support things like mnp4 and 5, v42, v42bis etc. one of the results of this is that the actual transport of data across a pstn or leased line with 2 async modems looks pretty much the same, and also achieves pretty much the same throughput as using 2 sync modems on that same line. Your comparison is only true for a plain async connection, but thats not what 2 async modems do. (and, when testing this on a network that has way more throughput then your async connection, you will plainly see this by achieving approx 110% of the theoretical async throughput, given you use things like a as high as possible dte-dce connection and hardware handshaking) > So a 64k ISDN channel is fair amount faster (about 20%) than two 33.6k > modems. > So... this is only true for a async connection employing 2 plain async modems without any error correction and such, which are almost extinct nowadays. Still there are a lot of advantages when using isdn, and esp. when compared to 2 33k6 connections the fact that its a single connection that can be setup quickly and requires very little overhead to be managed is where your potential performance gains are. Bart To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-isdn" in the body of the message