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56k modems relied on digital trunk lines

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Re: 56k modems relied on digital trunk lines

#21

Post by hylaride »

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.

Ha! My mom worked as a build engineer at BNR (later Nortel) in the 1990s and we got a free 2nd phone line for her to dial into work (99% used by me and my brother for internet). She could have gotten ISDN had it been available in our small town, but alas...

Re: 56k modems relied on digital trunk lines

#22

Post by topranks »

immibis wrote: post #2

Isn't it the opposite of the headline? Modems were hamstrung by digital phone lines you didn't know we had. One final trick allowed them to match, but not exceed, those digital lines.

Yeah kind of. The u-law sampling of audio to produce the 64kbit audio channels in ISDN isn’t good for encoding a signal created by a modem.

But if it was a direct copper pair end-to-end then attenuation and electrical other characteristics would have made it hard to achieve the higher speeds, this is the Shannon limits they mention.

Re: 56k modems relied on digital trunk lines

#23

Post by grishka »

Now I'm curious about how this worked in my city where we most definitely didn't have anything digital to our phone system at the time. As in, you had to use pulse dialing, and sometimes, rarely, your calls would glitch such that you would hear someone else talking over your call. Yet I remember consistently getting 40-something kbit over that.

Re: 56k modems relied on digital trunk lines

#24

Post by smittywerben »

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.

You have an eye for quality. They should make an Apple voice dongle for that. Inside joke. Signing off.

Re: 56k modems relied on digital trunk lines

#25

Post by hylaride »

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.

Or gaming. I never got good at quake because of it. IIRC they added hardware compression to the later versions (I think starting at 33.6?) that added latency, too.

Re: 56k modems relied on digital trunk lines

#26

Post by Sohcahtoa82 »

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.

As a kid, we didn't have ISDN, but we did have a second phone line dedicated to the modem.

My dad ran a BBS from like 1992 to 1995, which started falling out of favor, especially as the users were getting more busy signals because the modem phone line was tied up with the internet connection.

Re: 56k modems relied on digital trunk lines

#27

Post by ljf »

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.

Re: 56k modems relied on digital trunk lines

#28

Post by xnx »

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.

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.

Re: 56k modems relied on digital trunk lines

#29

Post by bigbuppo »

p1mrx wrote: post #13
chrsig wrote: post #3

ah, good ol' capping out at 26.4kb/s...until 2005

We were stuck at 26400 until 2001, when DOCSIS reached the area. I recall hearing speculation that a https://en.wikipedia.org/wiki/Pair_gain was the cause. Around 2000, I saw a crew pulling new phone lines through the neighborhood because everybody was getting a second line and they were running out, but even after switching to the new copper, we were still stuck at 26400. 20+ years later, it looks like 25/5 ADSL is…

More than one A-to-D conversion would knock it down to no more than 33.6. Pair gain units would cause problems. Bridge taps and load coils could also be problematic, but that was much more of a concern on DSL. Older amplifiers had very narrow filters and would also cause slow speeds. Echo cancellation hardware would ignore the in-band signal to get out of the way and cause problems.

As there was no legal compulsion to get them to act Bellsouth wouldn't do anything to help slow connect speeds for internet dialup. The trick was to lie and say you were having problems sending a fax, then they were required to act. They wouldn't even worry about testing first, as it was quicker to just re-engineer the line to the best practices of the day.

Re: 56k modems relied on digital trunk lines

#30

Post by shagie »

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.

There was also that period of time when Ricochet was available in some places.

https://en.wikipedia.org/wiki/Ricochet_(Internet_service)

Wireless 56k baud. So you could take your luggable laptop circa 1994 with you and dial in to work... given you lived in SF.

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