> Tragically there was nothing simple about ISDN

I’ve been working with some old telco equipment as part of a handful of projects and lord, has this hit me. Particularly some old PRI terminals I have are throwing me around left and right.

Interesting. In many European countries ISDN was widespread in the mid-to-late ‘90s. There were millions of customers in Germany alone, I think.

It was slow compared to the DSL connections that replaced it, but I don’t remember hearing too many negative things about ISDN reliability.

(I bet the only real legacy of this technology is the album by the Future Sound of London which is named ISDN.)

I could have this wrong but we had offices in Amsterdam and Berlin and ISDN in Europe wasn't nearly as polluted with old standards as it was in the US. I don't even think a 56kbps B channel was an option in Europe. I stood up dial plants in both continents and I distinctly recall it being plug and play over the pond.

We also used the ISDN to back up our circuits and Cisco had a pretty cool demand system that would just use what was needed to service the demand.

The most brutal thing I saw was when someone compromised a customer ISDN router (the small Ascend boxes with the curses UI) and changed the creds to login to their ISP and disconnected it and forced it to redial repeatedly. The local telco charged you for every ISDN call if it was a business line and since ISDN call initiaton/setup are instant - they had a several thousand dollar phone bill. I recall seeing the RADIUS server getting slammed with auth failure for days when that happened.

Yep!!! We had to tweak some settings because the router would constantly flap channels during DR tests and we were getting billed for the call setups (international ISDN calls were not cheap lol).

It was cheaper to have stable excess capacity.

ISDN was pretty much plug and play when I had it back in the day. The gateways were available off the shelf (IIRC mine came from CompUSA) and you could get them with either one or two B channels, as I recall.

That's BRI ISDN. PRI has a lot more channels. Also, there was dial setup and PPP vs IDSN bonding. So it can be complex.

Yes indeed. I had the pleasure to work for Ascend Communications for 4 years. The bulk of our business was the Ascend Max TNT that could terminate dozens of PRI lines into hundreds of digital modems. They were the bread and butter for early ISPs. For BRI lines, there was the Pipeline 50, remarkable little box with a BRI input and Ethernet output. Good times.

I was a big MaxTNT customer. The cooling on those were interesting. Also worked with the earlier Cascade BSTDX 9000 and CBX 500.