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56k modems relied on digital trunk lines

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Re: 56k modems relied on digital trunk lines

#71

Post by cantrecallmypwd »

plorg wrote: post #39
OhMeadhbh wrote: post #17

Yup. I worked on the "Rapport" series of switches at Bell Canada. It was DS1 (Digital Signal 1) out one end and a rack full of Zyxel modems on the other side. The idea was RBOCs (Regional Bell Operating Companies) would put these in their CO (Central Office) and terminate 56k modem signals over the analog "last mile" loop to the customer premises and then do Frame Relay over the phone company's data lines to your ISP…

Revealing my ignorance here, but was (is?) there a telephone equivalent of anycast such that, say, the 1-800-... Or 1-900... numbers would be routed differently based on location? My basic knowledge of phone systems suggests it would at least be possible.

911 and 0 (operator).

Re: 56k modems relied on digital trunk lines

#72

Post by cantrecallmypwd »

sureIy wrote: post #5

That reminds me of my short time with ISDN and the amazing availability to receive calls on the second line without forcing me offline.

Both our ISP and the phone company charged for every BRI data "call" placed and for minutes connected rather than a flat rate on a business-class ISDN line. I discovered IBM AIX's web browser package contained a telemetry background process that dialed home to Big Blue every 2 hours, causing our Cisco 1604 router to dial-on-demand even when no one was in the office. A simple deny IP ACL fixed that problem. There was no opt-out and no mention of it, and it never became a story that it should've been.

Re: 56k modems relied on digital trunk lines

#73

Post by Synaesthesia »

bryanlarsen wrote: post #54
Synaesthesia wrote: post #41

I could tell what connection speed my modem was going to be by the sound of the handshake. There were distinct sounds for all the different modes. I remember us getting our first modeum, it was 800 baud! Then we moved to 2400, 14.4, 33.6 and eventually all the way to 56k.

800 baud? Do you mean 300 baud? 800 baud is not a standard speed so if they did exist you'd have to supply both ends of the connection..

Oh yeah it was 300!

Re: 56k modems relied on digital trunk lines

#74

Post by calamity_elf »

stuff4ben wrote: post #6
sureIy wrote: post #5

That reminds me of my short time with ISDN and the amazing availability to receive calls on the second line without forcing me offline.

That 128Kbps on ISDN was the like the gold standard back then! I knew some sysadmins who had that installed to their homes so they could be available at any time. All paid for by the company they worked for.

I used to use 128Kbps bonded ISDN at home through BT Home Highway and an ISP called Red Hot Ant who had fixed price unmetered internet access.

And I accessed the heck out of that connection (until the ISP went bust, wonder why?), and was very much a Q3A LPB during that time.

Re: 56k modems relied on digital trunk lines

#75

Post by fhars »

paulmac_ie wrote: post #69
Sesse__ wrote: post #61

Earlier quoted context omitted.

192 kHz? That makes no sense, unless you want to have a telephone conversation between bats.

192 kHz is the sampling rate, not the sound frequency.

That still makes no sense, unless you want to have phone calls between bats.

Re: 56k modems relied on digital trunk lines

#76

Post by cjrp »

OhMeadhbh wrote: post #18
xnx wrote: post #7

Earlier quoted context omitted.

I'm still mad that they high-quality voice audio possible through ISDN didn't become ubiquitous. It's ridiculous to hear the clipped frequency range of a plain old telephone line during radio interviews in 2025.

I think it was ubiquitous. NPR in the 90s and 2000s used ISDN to allow many of their commentators to work from home. I think where you hear those crazy 8KHz clipped calls is where it's not an option. Mostly these days remote radio and podcast interviews I hear remote participants sound more like they're on mobile phones: variable voice quality with an almost unbearable latency.

Apparently it was still used for commentators at the BBC until 2023 https://www.linkedin.com/pulse/ode-isdn-paul-furley/

Re: 56k modems relied on digital trunk lines

#77

Post by kreddor »

TIL why upload on 56k modems were capped on 33.6k. I always wondered about that. Super interesting stuff!

I also remember back in the day that my 56k modem would often only connect at like 48k or so, especially when it was raining. I guess living far out from the city made the connection more noisy?

Re: 56k modems relied on digital trunk lines

#78

Post by wffurr »

timthorn wrote: post #67
rasz wrote: post #47

Earlier quoted context omitted.

> DS1 (Digital Signal 1) out one end and a rack full of Zyxel modems on the other side Why use real physical modems when you already have subscribers signals converted to convenient digital form in DS1 bundle? Wouldnt it make more sense to put a box with one fat DSP doing 24 modems all in bulk inside a box with DS1 and Ethernet sockets at the ISP location instead?

I was working for one of the telco equipment firms around that time. We made a box that would terminate TDM trunks and had it in the lab. I was installing Windows 2000 on a PC in the lab (manual disk swapping required) when, hidden behind another rack, several shelves full of physical modems all started calling the box at once, speakers on.

I am trying to imagine the racket that must have made. Amazing how vivid that modem sound is in memory.

Re: 56k modems relied on digital trunk lines

#79

Post by aa-jv »

I had made a small career on building Internet Service Providers in California, in the early days, and will never forget how liberating it was to carry my laptop to the Griffith Park observatory with a fully-charged Ricochet modem plugged in, communicating to my house down in Los Feliz, where another Ricochet modem gateway'ed me to the Internet via the house 56k line ..

It was truly astonishing to be up there, checking email.

A few, what seems very short, years later .. and now it is just normal.

Re: 56k modems relied on digital trunk lines

#80

Post by shrubble »

plorg wrote: post #39
OhMeadhbh wrote: post #17

Yup. I worked on the "Rapport" series of switches at Bell Canada. It was DS1 (Digital Signal 1) out one end and a rack full of Zyxel modems on the other side. The idea was RBOCs (Regional Bell Operating Companies) would put these in their CO (Central Office) and terminate 56k modem signals over the analog "last mile" loop to the customer premises and then do Frame Relay over the phone company's data lines to your ISP…

Revealing my ignorance here, but was (is?) there a telephone equivalent of anycast such that, say, the 1-800-... Or 1-900... numbers would be routed differently based on location? My basic knowledge of phone systems suggests it would at least be possible.

Yes, but it would usually be based on the first 3 or 6 numbers of your phone number. The first 3 are of course “area code” and the 6 are called “NPA-NXX”. This has blurred some due to line number portability and cell phones.
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