Date: Tue, 19 Mar 96 15:19:49 MET From: Greg Lehey <lehey.pad@sni.de> To: jkh@time.cdrom.com (Jordan K. Hubbard) Cc: hackers@freebsd.org (FreeBSD hackers) Subject: Re: ISDN: "modem" or board? (Was: Microsoft "Get ISDN"?) Message-ID: <199603191422.PAA14455@nixpbe.pdb.sni.de> In-Reply-To: <1434.827244618@time.cdrom.com>; from "Jordan K. Hubbard" at Mar 19, 96 6:10 am
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>> 1. Speed of a connection. Some people say "the bottleneck is the B >> channel, so you can use async instead". Well, yes, assuming your >> machine isn't doing anything else. To run 2 B channels flat out, >> you need a 230 kb/s line, which with standard el cheapo 16550As > > You, uh, would? 64+64 = 128Kb/s using my own calculator! :-) No, that's abusing your calculator. Async bytes are 10 bits (8 bits, start and stop), whereas sync bytes are 8 bits. So you'd need at least 160 kb/s async. But where can you get that speed? >> ISDN board, the software talks directly to the D channel. On an >> ISDN "modem", you need first to establish (serial) connection with >> the "modem", it then needs to interpret your commands and talk to >> the D channel. This is bound to take longer, but the question > > The difference is not noticable at all with my own pair of TAs - from > connection to the serial port to a login prompt on freefall takes all > of 1-2 seconds. The lengthy bit is the chat script login and SLIP > negotiation phase - something I couldn't avoid with a card, I think. Aha. Yes, you can. With a card, there is no chat script or login, no more than there is if you connect to a different system via Ethernet. >> 4. Price. I think some people have not read the messages carefully. >> I just ordered another batch of boards for DM 133 each, about $90. > > Lucky you - you can even get them! :-( > > I've had mine on order from Teles for 5 months now. Still no > availability in the U.S. I looked around avidly for a pair of boards > when I first got my ISDN line and finally punted in favor of the two > $349 ADTRAN TAs that were available Right Now. > > The ADTRAN TAs are also nice in that they do channel bonding > transparently. Yes, this is something we still need to investigate. ISPA, the DOS program I'm using on my 286 at the moment, also does this (with configurable thresholds per address). > You just configure the modem for bonding mode 1 and it > automagically makes two outgoing calls and bonds the B channels > together for a single "fat pipe". If it does it automatically, you end up paying twice as much for your connection, even if you don't need the bandwidth. You need some form of load detection to make it economically viable. > I've talked with Helmuth a little > about this and it doesn't look like it's anywhere near as easy to do > with the TELES cards, though I may have misunderstood him. You could be right. I don't think anybody over here has really investigated the requirements. Maybe Dietmar knows. > Oh yeah, the TAs also support standard Hayes dialing. I'm not looking > forward to figuring out how to use the dialer interface for the boards. It's much simpler than standard Hayes. With ISPA, you just have a list of IP addresses and phone numbers. I know how to set up SLIP and PPP on analogue modems--that's one of the reasons I prefer ISDN boards. I still haven't investigated the exact formats for the FreeBSD solution--I suppose I should spend some time getting the doc up to scratch. > Don't get me wrong - I STILL want a pair of boards because I want to > have a full 128K/sync connection and get that last 25% of performance > out of the line, but I think that for some people a pair of TAs is the > most no-brainer, plug-it-in-and-go-today solution you can buy. You want me to order a couple for you? Greg
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