On the ISP side, ISDN was a crucial part of scaling out dial-up ISPs. CLECs (Bay Baby Bells) would route calls from geographically large calling areas --- all of Chicago, say --- to a single colo cage on an ISDN PRI. Access concentrators (then called "terminal servers" --- Portmasters, Ascend routers, Cisco AS5x00s) would take 56k modem calls on individual PRI channels.
What Was ISDN?
21–30 of 164 posts
Re: What Was ISDN?
#22Man, the idea that ISDN was going to last 50 years has to be one of the bleakest Bellhead memes I think I've ever heard. "You will only have 144kbps and be happy."
It's a service framework for subscriber based circuit switched connections. The modulation format is separate and I doubt they expected to keep such a meager encoding for the long predicted life of the network.
The error was in not seeing packed switched networks as the clear winner not in choosing a modulation scheme that was designed to bring maximum bandwidth over existing copper infrastructure.
In any case, the strength was that you could bond up to 24 channels in a North American PRI package, which is what a lot of businesses considered their "T1" service, or used as a mixed group of DID and LOOP channels for calling.
Interestingly, in the end, they used bonded ADSL to provide an encapsulated 24 port PRI "circuit" to the customer using just 4 wires.
Re: What Was ISDN?
#23in the mid-90s it was often the only option for >14.4kbps internet in residential areas. unfortunately the tariffs charged by the minute for voice and data calls so it was prohibitively expensive (at least for our household). the hack (in the US) was that ISDN was often offered as part of "centrex" service which was a sort of phone company managed PBX-as-a-service offering. so rather than businesses setting up their…
Interesting. v.34 ratified in 1994 supported 33.6 kbit/s. In at least some areas POTS calls to local prefixes were unmetered. ISDN BRI had similar, if not identical, tariff.
i guess you're right about 33.6kbps... point stands, if you wanted to go faster than analog modems in residential settings, before DSL and DOCSIS, ISDN was often the only game in town.
BRI did not have free local calling with pacific bell at the time and "local long distance" or metered within NPA calling was quite expensive- often times a lot more expensive than actual long distance calling.
Re: What Was ISDN?
#24ISDN was a great upgrade for me in the 1990s, and once I found out how to couple two lines into one "massive" 128k, it was pretty mind blowing. Connecting to the Internet was also snappy (as opposed to dialup with the whole modem song) and could even be done on demand if you were brave.
Well, it wasn't actually 128k. Technical reasons limited it to 112k. That's why 56k instead of 64k modems. There was the Shotgun Modem which required 2 separate phone lines, but would bind them together. I never bothered reading up on how binding 2 PPP connections worked, but I guess it worked well enough that it was a legit product being sold. I went from 28.8k to ISDN, so I skipped the 56k altogether. Of course, IS…
You're right the BRI was actually 144k, 2x64k B channels and 1x16k D channel. 112k was available on misconfigured hardware and gimped bit-robbing lines where some of the bits on the B channels were used for signaling in lieu of a D channel.
Re: What Was ISDN?
#25Don’t forget Frame Relay, which was a good complement to ISDN.
Don't forget ATM, which was a good complement to ISDN.
Re: What Was ISDN?
#26Don’t forget Frame Relay, which was a good complement to ISDN.
Frame Relay was horrible, and the bane of our existence at the ISP. We had a wide variety of customer connections, from dialup to an honest-to-God 14.4Kbps digital leased line, to 56K and T-1 leased lines and some T-3s in our backbone. Our manager was a huge proponent of SMDS; in fact the SMDS diagrams made liberal use of the "cloud" icon to depict connections going in and out of the telco's switched network. He was…
FR was problematic because the FR networks were oversubscribed, which was actually one of the benefits of the technology. The tech support for FR was also lackluster at best. The nice thing about FR was that you could aggregate multiple connections on one piece of equipment and pay based on usage rather than committed bandwidth.
Re: What Was ISDN?
#27I used ISDN internet for a few years in the 90s before DSL became available. It was a big improvement over normal dial-up because you could still use the phone while online. Or use two lines for 128kb downloads if you weren't expecting a phone call.
Re: What Was ISDN?
#28Got ISDN as a previous job as parttime helpdesk employee at an ISP. Together with the rise of numberous dail-up providers, including the legendary Superweb. It would allow free internet against a fix rate, not paying per minute, which was something new for the Netherlands. It would only allow one or two hours after it would disconnect you and you had to redial. Due their succes getting dialed in again could take quite long (too many users, not enough lines). So I wrote code/script and made changes to the Linux distribution to allow me to dial with my second line as part of my ISDN, starting ten minutes before I would get disconnected, and “transfer” the connection to the new connection when it was finally able to dial-in, hence having internet 24hours a day. Good times! Superweb didn’t exist very long…
Re: What Was ISDN?
#29I remember visiting relatives in Switzerland in the 90s and it was the first time I’d seen ISDN - felt like they were living in the future while we were still on dialup in the US. I was thinking earlier today how when I was that age how amazing it would be to have fiber someday - has taken 25 years but I finally have it at home, and it still isn’t fast or reliable enough
Re: What Was ISDN?
#30Serbia (former Yugoslavia) was mostly in turmoil in the 90s, and while I did get online using dial-up in 1995, new tech was (very) slow to arrive: I used ISDN for a few short years in early 2000s before ADSL finally arrived. It was amazingly reliable even in Serbia. But compared to the regular 20V phone line, ISDN used something like 120V (which I learned by carelessly changing the connector like I used to on the reg…
20V? Germany has traditionally used 60V. The current spec allows 20V - 105V https://www.nostalgietelefon.de/beachten/1TR110-1%20Ausgabe%...
Ma Bell used -48v DC in the US, which was backed by a giant lead acid battery at the local exchange. It was quite common to have ADSL circuits working during major power outages, so long as the modem and servers were on redundant power. It might still be worth coming up with a USB charger circuit, but I assume current draw is metered.