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56k modems relied on digital trunk lines

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Re: 56k modems relied on digital trunk lines

#51

Post by icedchai »

rasz wrote: post #47
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…

> 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?

This did happen eventually. In the late 90's, various companies (Cisco, Ascend) provided boxes that could handle 24 modems on a single T1 port (PRI or channelized T1.) This massively improved ISP port density. Before that, it was racks and racks of modems...

Re: 56k modems relied on digital trunk lines

#52

Post by icedchai »

phil21 wrote: post #34
stuff4ben wrote: post #6

Earlier quoted context omitted.

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.

The most bang for buck "employee benefit" I ever offered to my guys back in the earl 00's was a T1 line to their home for free. We could do this since local loops to most folks were about $150-200/mo, and we already had a channelized DS3 terminated at our rack at a local datacenter for our phone banks. If you bought your own DS1 retail you'd be paying upwards of $1k/mo back then to a provider. It was by far the best…

I worked at an ISP that gave dedicated ISDN and 56k frame relay lines as a benefit in the late 90's. T1 would've been amazing!

Re: 56k modems relied on digital trunk lines

#53

Post by cosmotic »

Synaesthesia wrote: post #42
numpad0 wrote: post #16

Earlier quoted context omitted.

24 [bit] * 192 [kHz] = 4.608 [Mbps]. Maybe not sensible to do so, but many people could have Discord calls in uncompressed "high-res" WAV. It's crazy that there aren't even 16bit/44.1k modes in most voice call apps.

Speech compresses really well, with modern techniques you can get it down a lot. The big issue with analogue landline phone calls is the audio bandwidth is so limited. It's not the full frequency spectrum, most of it it cut off.

For some context, wikipedia has a good table and diagram of codecs that do well at low bitrates, many of which are very old (G.722 from the late 1988, Speex from 2003, Opus from 2012 for a few examples)

https://en.wikipedia.org/wiki/Comparison_of_audio_coding_for...

https://en.wikipedia.org/wiki/Opus_(audio_format)#Quality_co...

Re: 56k modems relied on digital trunk lines

#54

Post by bryanlarsen »

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..

Re: 56k modems relied on digital trunk lines

#55

Post by roygbiv2 »

ljf wrote: post #27
wkat4242 wrote: post #10

Yes these modems were almost-ISDN (minus the razor fast call setup). And required a full digital backend to work. They could only do 56k6 in one direction, to the user too. But they were made for internet access so that didn't really matter.

I remember my brothers friend in rural Portugal having one way satellite Internet back in the 90s to very early 00s - you used a standard dial up for the upstream, but with a satellite dish got much much faster downloads. Blew my mind that you could go out one way and receive another and still get a functioning (and fast) connection.

I remember reading about this back in the day. I seem to recall the latency being a killer.

Re: 56k modems relied on digital trunk lines

#56

Post by pimlottc »

To be clear, this was well known at the time. It was advertised that 56k was for download only and required an ISP that supported it. For those living in rural areas, there often weren’t any local options (long distance was certainly not free in those days). But for those who could get it, it was definitely a big improvement.

Re: 56k modems relied on digital trunk lines

#57

Post by wkat4242 »

icedchai wrote: post #14
wkat4242 wrote: post #10

Yes these modems were almost-ISDN (minus the razor fast call setup). And required a full digital backend to work. They could only do 56k6 in one direction, to the user too. But they were made for internet access so that didn't really matter.

ISDN had much, much better latency than even 56k modems. Modems were around 150ms minimum. ISDN was often in the sub 20 ms range. This made a big difference for chatty protocols like HTTP, telnet, etc.

True, though in those days that didn't really matter except for gaming. The bandwidth was so low and the web going in content so fast that the local uplink bandwidth was usually congested causing delays due to queueing and pending acknowledgements. Switches and routers weren't quite as optimised for low latency either. A lot of local networks were still 10base2 (or 10baseT with hubs, not switches) so collissions added further latency.

What I loved the most about ISDN was the quick call setup. Took like 1 second max and you had a 64kbit channel. 56k modems went through a dialling phase, a connection phase, endless handshaking...

Re: 56k modems relied on digital trunk lines

#58

Post by numpad0 »

Synaesthesia wrote: post #42
numpad0 wrote: post #16

Earlier quoted context omitted.

24 [bit] * 192 [kHz] = 4.608 [Mbps]. Maybe not sensible to do so, but many people could have Discord calls in uncompressed "high-res" WAV. It's crazy that there aren't even 16bit/44.1k modes in most voice call apps.

Speech compresses really well, with modern techniques you can get it down a lot. The big issue with analogue landline phone calls is the audio bandwidth is so limited. It's not the full frequency spectrum, most of it it cut off.

I have no problems with Opus or mp3 at low bitrate, in the same way I have no problems with microwaved food. I just think it's crazy that no one is doing 4Mbps audio while we're routinely streaming 20Mbps video as cheap distractions.

Re: 56k modems relied on digital trunk lines

#59

Post by ubercore »

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…

Compaq Presario catching strays.

Re: 56k modems relied on digital trunk lines

#60

Post by Sesse__ »

xnx wrote: post #7
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.

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.

Modern cellphone networks support wideband codecs, e.g. AMR-WB.
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