56k modems relied on digital trunk lines

Post by Creator56 » Wed, Mar 12, 2025, 4:56 PM UTC

linsomniac wrote: post #85

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?

You're thinking about the Livingston/Lucent Portmaster 3. https://osmocom.org/projects/retronetworking/wiki/Livingston... These were great boxes, and the only way you could get 56K was to call into an ISP with one of these or similar on their end -- the trickery that allowed 56K relied on one end being fully digital. I was working for an ISP around that time and we had a bunch of Portmaster 2s connected via RS-232 ca…

Post by quink » Mon, Mar 17, 2025, 10:04 PM UTC

quink wrote: post #50

quink wrote: post #38

Earlier quoted context omitted.

Of course ancient telephone wiring can carry 1 Gbps. The real question you always, always, always, need to be asking yourself is: Over what distance? Make that distance short enough, as has happened with FTTN, or FTTC deployments in a whole heap of places, you're basically building a network that's, and I'll keep this very brief, subpar. Since you mentioned a UK context there, Openreach rolled out an upgrade that kep…

OK, had a look through the linked paper. The big graphs, on page 8, tell you that if you decrease the twist length - which would entail relaying all the copper in the entire network, at which point you may as well put down fibre instead - you will get -20 dB at 10 GHz over a distance of 0.5m, 50cm, less than two feet, instead of -25 dB in the worst case. In other words, instead of losing 99.7% of the signal over that…