There used to be a lot of nice material on this subject but a lot of it has been obsolete and rotted away from the web over the last 15-20 years. The larger dial-up ISPs used Cisco AS series boxes (or equivalent) with PRI (i.e.: phone over T1) connections (24 lines/each) to a centralized RADIUS server for authentication. They are/were the last hold outs providing dial up.
Smaller ISPs were more of a '94 to '99 thing. Usually they used cyclades or equivalent serial port cards with up to 16 serial ports per card and an external modem per port. Eventually this morphed into boxes with multiple modems in them and access servers that did the ppp termination and the authentication (to a RADIUS server) as scale increased. US Robotics was probably the best reputed player in the modem space.
In my smaller regional ISP we started off using USR courier and sportster modems with Cyclades cards before moving over to Livingston Port masters. I ended up selling the company before moving to all digital incoming lines (needed to support 56k modems).
Did exactly the same.... We had sporters hanging off the wall for a while (couldn't pack them tightly due to the crappy ventilation on the Sporters, but they were light, so clamping the cables to a suitable plate and fitting it to the wall worked great....)
The local telco had problems supplying enough lines from the nearest exchange, so they ended up hanging a thick cable bundle in the trees for several hundred meters, make a hole in one of our windows and put a large multiplexer cabinet in our office... Then three months later we moved to different offices - they were not pleased.
We got metal wire shelves and kept each shelf fairly close together (about 6-8 inches). We had 10 selves per rack and 18 modems per 3ft x 6ft shelf. 10 racks and related additional hardware (switches, terminals, routers, CSU/DSUs, etc) fit in about 600sq ft of office space with space to spare for technician workbenches. Could do much higher density these days of course, but it was the mid-90s and we thought we were doing good at the time.
We didn't quite get to the size where we needed that before we sold off the dial up business (for a pittance; we contributed to accidentally set off a price war in our market with incumbents with deep pockets - it was no fun, but I learned a lot)
I got lucky in that regard. The larger company in our area decided it was better to buy us out than compete on quality of service, so we were in a position to better negotiate terms of sale.
I'll dig up photos of the ISP I founded back in 1993. I've got the evolution of it from 1993 till I sold it in 97, but they were all film photos for obvious reasons. Surprised I never took the time to post before.
I can't speak for early early dial up infrastructure, but by the turn of the century the equipment involved was not all that impressive to look at.
A typical configuration would terminate the analogue lines over ISDN, which supported somewhere up to 30 B channels ('voice calls') over a single cable, running alongside one or two Ethernet cables to a single router with one or more modem option cards installed.
Your edit mostly got it right with the exception that it wasn't commonly called a T-1 or E-1 and the numbers are slightly off.
* ISDN BRI = two 64k B channels and one 16k D channel
* ISDN PRI over T1 = twenty three 64K B channels and one 64k D channel
* ISDN PRI over E1 = thirty 64k B channels and one 64k D channel (time slot 0 on the E1 was used as a sync channel and wasn't considered a B or D)
T1/E1 was considered an analog circuit with 24 or 32 respective 64kbps voice channels using in band signaling effectively limiting each channel to 56k. ISDN PRI used the same cabling and channel separation, but instead ran a digital circuit with out of band signaling enabling the full 64k to be available for voice and data. ISDN PRI (and BRI) also allowed the option to be packet based (similar to X.25) rather than circuit switched for data transmission.
In the 90s in my little corner of the mid Atlantic US at least, it was very commonly called a T1 or DS1 and the terms were used interchangeably even though they refer to slightly different things (at least by sysadmins; use the terms wrong around a telecom equipment engineer and you'd likely get corrected).
I'm aware the misnaming was common, but it's a bad idea to do so. There's a pretty big difference between a T1 and a PRI in practice when used as a data only circuit. For one, the T-1 is a fair bit faster.
I worked for a large UK organisation that had cut back on their dialup access but still had 50 or so modems in racks for field workers to dial in to to get their email etc. Also some site to site links remained a dialup connection.
Sorry, no fancy pictures or anything interesting, just reminded me of the time.
A few Datacentres I know have POTS/ISDN capability as they host a fair view VOIP companies. I assume at some point that VoIP call needs to get into the existing telephone network somehow. Also, companies would locate their telephony stack in a DC and route over ethernet just so the kit was more secure and in disaster scenarios they pick up anywhere.
Yup. Lotta places will now give you 1Mbps 95% on FastE inclusive with a service contract, if you ask nicely, and are taking a cage with 20+ racks. Datacenters which ask you to pay it's usually <$50 MRC.
Would guess the transition is slow because if it ain't broke why fix it, and its often a lot more than just provisioning a new circuit, you have to update process documentation, etc.
I worked at a couple of small ISPs in the mid 90's, and built the dialup infrastructure of one from scratch. I remember using Xylogics Annex terminal servers connected to either 16 or 32 individual USR modems. There were stacks of modems, each with its own power brick, serial, and RJ-11 connection.
This was a few years before everything went digital with PRI lines (T1s that let you do digital modems, basically.)
https://www.patton.com/technotes/build_yourself_an_isp.pdf
http://www.gwi.net/behind-the-scenes-of-a-90s-internet-start...
https://news.ycombinator.com/item?id=8352432
The absolute minimum, and representative of the very first dial-up ISPs: http://www.linuxjournal.com/article/2025
http://www.datamation.com/erp/article.php/615281/My-own-priv...
There used to be a lot of nice material on this subject but a lot of it has been obsolete and rotted away from the web over the last 15-20 years. The larger dial-up ISPs used Cisco AS series boxes (or equivalent) with PRI (i.e.: phone over T1) connections (24 lines/each) to a centralized RADIUS server for authentication. They are/were the last hold outs providing dial up.
Smaller ISPs were more of a '94 to '99 thing. Usually they used cyclades or equivalent serial port cards with up to 16 serial ports per card and an external modem per port. Eventually this morphed into boxes with multiple modems in them and access servers that did the ppp termination and the authentication (to a RADIUS server) as scale increased. US Robotics was probably the best reputed player in the modem space.