Date: Thu, 14 Mar 96 17:17:39 MET From: Greg Lehey <lehey.pad@sni.de> To: jgreco@brasil.moneng.mei.com (Joe Greco) Cc: hackers@freebsd.org, isdn@muc.ditec.de Subject: Re: Microsoft "Get ISDN"? Message-ID: <199603141621.RAA24997@nixpbe.pdb.sni.de> In-Reply-To: <199603141610.KAA22055@brasil.moneng.mei.com>; from "Joe Greco" at Mar 14, 96 10:10 am
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> >> I don't like "ISDN modem"s for a number of reasons: >> >> 1. They're more expensive > > How do you figure? $300-$400 isn't bad. You pay $225-$250 for a decent > V.34 modem... Sorry, I meant "more expensive than a cheap ISDN card". See below--over here they cost $100 odd. >> 2. In my experience, they're *much* less reliable. > > I've _never_ seen a failure. On the other hand, the Combinet ethernet > bridge stuff we use at work is tempramental, unreliable, and difficult to > configure. I generally point people away from that particular solution. Again, the comparison is with ISDN boards, not with modems. I don't know the Combinet, but the ISPA/PC-ROUTE stuff I use is disappointingly reliable :-) (In case you don't understand, it lessens the incentive for me to switch over to the FreeBSD software). >> 3. They require to be connected by an async line. Considering that >> 128 kb/s ISDN translates to 160 kb/s async, it's evident that >> you can't keep up the same speed. In addition, conventional "El >> Cheapo" serial interfaces lose data at this speed. > > True (well, I haven't seen lossage using 16550's, but anyone using 16450's > deserves what they get). I think you would do at 160 kb/s. >> 4. You can't run raw IP over them, mainly because of (3). > > I don't see people running "raw IP" over sync lines, either. It's generally > run via PPP or Cisco or some other protocol.. you can certainly run PPP or > SLIP over an async ISDN connection as well. You don't in the US, but it's the standard (if not only) way to do it over ISDN here in Germany. >> 5. You can't use them for connect on demand. The board solution can >> allow the system to disconnect after a certain idle time, and then >> reconnect when another packet arrives (from either side). > > Eh, really????? Wow. And here I thought iijppp had these features built > in. Silly me. ;-) Looks like I might be behind the times here. Is this with the call setup time you mention below? >> 6. I'm not sure about this, but I believe call setup is slower. On a >> direct connect board, call setup is round 2 seconds. This is >> particularly important for point (5). > > Call setup for a dual-channel ISDN link around here is about two seconds, > maybe three, but it's doing more work than a single link. > > I have no idea why you think a direct connect board would be faster. You > are being limited by the rate at which you can chat with the switch and how > fast the switch can set up the call (possibly involving more than one > switch). Well, for one thing you need to transfer your data to and from the "modem", and in most ppp environments I've seen various delays. But to be honest, I've never bothered trying it with ISDN "modems". The only ones I have used (Elink) were so temperamental that I could hardly get an interactive connection running. >> > You can also get ISDN modems that plug into your serial port which >> > are then used as point to point links (ppp, slip). >> >> As the Germans say, you can also put rivets in your ears, hang slices >> of sausage on them, and claim you're a dachshund. > > I guess I don't understand what your problem with this is. ISDN terminal > adapters were _designed_ specifically to do these sorts of things, and in my > experience they are more reliable and less tempramental than analog modems. As I said above, I'm not comparing them with analogue modems, though if I did, I think the Elinks would still lose. But I'm more than prepared to believe that this is a problem with the Elinks. > In my opinion, it's always great when you can leverage off of pre-existing > technology. The TA's play right into the fact that support for serial > devices like modems is widespread and well tested. It's a zero effort > solution.. Hmm. I'm not in favour of change for change's sake either. But I've had much pain running PPP and SLIP on analogue links, and once I got past the pain of setting up ISPA (mainly the result of impossibly bad documentation), it just works. The router never crashes, I always (well, almost) get my connection, and I need zero setup on any other machine in the net (well, I have to tell them the default gateway). I think the bottom line here is that the kind of ISDN boards used in Germany are hardly available in the USA. As I say, that's beginning to change, and I'd be interested to hear what you have to say after you've installed them and got over the teething problems. Greg
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