Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

56k modems relied on digital trunk lines

hackaday.com

Post reply on HN
Print view View original

61–70 of 143 posts

Re: 56k modems relied on digital trunk lines

#61

Post by Sesse__ »

numpad0 wrote: post #16
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.

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.

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

Re: 56k modems relied on digital trunk lines

#62

Post by DecentShoes »

xnx wrote: post #28
OhMeadhbh wrote: post #18

Earlier quoted context omitted.

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.

Every once in awhile the stars align and I randomly get an "HD" voice call. It's disorienting to both me and the other party how good the quality is.

HD Voice is genuinely what it's called:

https://www.microsoft.com/en-us/microsoft-365/business-insig...

They really do sound alot better. It always reminds me of the first time I ever made a FaceTime call, in 2010, and the high quality audio was just as interesting as the video.

Re: 56k modems relied on digital trunk lines

#63

Post by DecentShoes »

hackthemack wrote: post #35

I have to wonder if the cap (theoretical) on the copper wires was more because of the technology standards in play at the time. Surely the copper wires could have handled more if they did not have to carry voice communication (with the old tech specs of the time) any longer? Ok. Searched around. Here is an article that states old copper could have carried 1 gigabit. https://www.newscientist.com/article/2317040-ordina…

It can carry 1 gigabit, over a few metres. I.e. Not even the length from the street to your house.

Australia tried this, it's physically impossible.

Re: 56k modems relied on digital trunk lines

#64

Post by [deleted] »

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.

[deleted]

Re: 56k modems relied on digital trunk lines

#65

Post by actionfromafar »

icedchai wrote: post #51
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?

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...

IIRC it was the only way to support 56k.

Re: 56k modems relied on digital trunk lines

#66

Post by timthorn »

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, the Intelligent Network was the big thing in the 1990s. It allowed for routing as you describe as well as calling cards and many other features: https://en.m.wikipedia.org/wiki/Intelligent_Network

Re: 56k modems relied on digital trunk lines

#67

Post by timthorn »

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?

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.

Re: 56k modems relied on digital trunk lines

#68

Post by somat »

hackthemack wrote: post #35

I have to wonder if the cap (theoretical) on the copper wires was more because of the technology standards in play at the time. Surely the copper wires could have handled more if they did not have to carry voice communication (with the old tech specs of the time) any longer? Ok. Searched around. Here is an article that states old copper could have carried 1 gigabit. https://www.newscientist.com/article/2317040-ordina…

it can carry more, the whole value proposition of dsl was a high speed link over existing cabling, I think the dial up limitation is what speed can you sneak over the existing speech focused analog signal processing equipment. where as the article explained by making that analog link as short as possible it could improve speeds quite a bit. dsl was what you could achieve over the same lines when you were not forced to constrain your signal to speech frequencies

Re: 56k modems relied on digital trunk lines

#69

Post by paulmac_ie »

Sesse__ wrote: post #61
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.

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.

Re: 56k modems relied on digital trunk lines

#70

Post by madwolf »

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.

Probably depends on the radio station and area but I work in one and we're actually using something much higher quality for remote radio, for example: https://www.prodys.net/portable-codecs-audio/quantum-lite-2/

If course it has to be pre-planned, someone needs to have the hardware with them. So sometimes there's a spontaneous connection over normal mobile phone. That's something that everyone has with them at all times.

Post reply on HN