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Ask HN: How did ISP's with dial-up servers work?

8 points by BorisMelnik ↗ HN
Ok I actually used to work for an ISP back in 2000 that did dial-up but never got to work on that end of the business.

How did it work? Did they have to have huge pools of modems for every person dialing in? I am totally clueless to this and found little info on this on the web. Have been thinking about this a lot lately and would really like to know.

14 comments

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hydrogen18
The phone company operates trunking lines, which multiplexes some large number of phone lines over a single physical medium. T1 for example is a common standard to deliver 24 voice lines over a single physical medium. Historically, you'd have equipment at both ends. One at at central office and one near a group of subscribers, like a street full of homes.

Basically the dial up server just had hardware that directly terminated the trunking line into it. The modem part might be done in software, might be done in hardware, or a little bit of both. By doing this it is practical to have a single machine serving 100s or even 1000s of customers.

BorisMelnik
wow thank you - that makes sense because I never remebr seeing huge banks of servers. there were definitely a few but I never remember seeing any kind of "rows of modems" or anything.

So you are saying (more or less) 1 T1 for every 24 lines or 24 customers?

icedchai
Each T1 gave you 24 lines. Generally, early ISPs were heavily over-subscribed, meaning there were many more customers than available phone lines. You might call in and get a busy signal!
hydrogen18
I remember getting up early on Saturday mornings so I could get connected the to the local FreeNet before all the lines were busied.
BorisMelnik
yes! I remember hanging up and reconnecting like 5x if I 'didn't get a good line' :)
kjs3
24 lines. As ISPs got bigger/more efficient, they moved to T-3/DS3 lines (672 lines per). I can only think of a handful of ISPs that went bigger than that. By the time OC-3 and larger channels became cost effective, the era of dial-up was pretty much over.
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wmf
Smaller scale ISPs did have shelves of external modems attached to remote access servers [1] which were often FreeBSD boxes. I don't know if they used regular POTS lines or channel banks [2]. Specialized RAS routers with multichannel soft modems [3] (e.g. from Ascend [4]) came out later.

[1] http://en.wikipedia.org/wiki/Remote_Access_Service [2] http://en.wikipedia.org/wiki/Channel_bank [3] http://m.eetasia.com/ARTICLES/1999JUN/1999JUN29_BD_NTEK_TAC2... [4] http://en.wikipedia.org/wiki/Ascend_Communications

icedchai
Early ISPs (before the mid 90's) had individual modems. I worked at one and we had stacks and stacks of modems - 100's of them - each with their own phone line, power brick, and serial cable.

By the late 90's, we had moved to digital modems using PRI lines. This provided the equivalent of 24 modems over a single T1 line.

lultimouomo
> I worked at one and we had stacks and stacks of modems - 100's of them - each with their own phone line, power brick, and serial cable.

Now that's something I'd love to see picture of!

icedchai
Unfortunately I don't have any, but it was truly a sight to behold. There were power strips chained 2 or 3 levels deep just to get enough spots to plug in all the bricks.
salem
There were definitely racks of modems at small scale ISPs in the 90's.

Once line speeds hit 56k and required more sophisticated equipment at the exchange/ISP, a lot of small ISPs got squeezed out because of the investment required, and sold their phone number and customer base.

A lot of consolidation started happening at that point, from what I remember.

iSloth
I work for an ISP in the UK and we actually still have some of the old dial up internet kit running in our exchange, 99% of customers are now on xDSL based services, however a few are still belligerent and don't want to move into the modern age, the equipment doesn't really cost anything to keep running so it's in effect free money for the business (other than power).

The technical side is basically a few Cisco AS5300 that terminate 2 to 4 E1's from the IMS based ISDN network, your effectively just dialling a number from your modem that is load balanced over these E1's. At the other side of the Cisco is your internet service, fairly simple and works well for what it is.

There can be other things in the mix like AAA (Radius) to authenticate the users, but as your charging for the call within the POTS network that's not always required, assuming that the internet and line provider as the same as in our case.

BorisMelnik
ah very interesting. thank you. I was assuming that everything would be completely different over there, and that a "POTS" would be completely different.