Comment by beagle3
16 hours ago
The real analog copper lines were kind of limited to approx 28K - more or less the nyquist limit. However, the lines at the time were increasingly replaced with digital 64Kbit lines that sampled the analog tone. So, the 56k standard aligned itself to the actual sample times, and that allowed it to reach a 56k bps rate (some time/error tolerance still eats away at your bandwidth)
If you never got more than 24-28k, you likely still had an analog line.
56k was also unidirectional, you had to have special hardware on the other side to send at 56k downstream. The upstream was 33.6kbps I think, and that was in ideal conditions.
The asymmetry of 56k standards was 2:1, so if you got a 56k6 link (the best you could get in theory IIRC) your upload rate would be ~28k3. In my expereience the best you would get in real world use was ~48k (so 48kbpd down, 24kbps up), and 42k (so 21k up) was the most I could guarantee would be stable (baring in mind “unstable” meant the link might completely drop randomly, not that there would be a blip here-or-there and all would be well again PDQ afterwards) for a significant length of time.
To get 33k6 up (or even just 28k8 - some ISPs had banks of modems that supported one the 56k6 standards but would not support more than 28k8 symmetric) you needed to force your modem to connect using the older symmetric standards.
The special hardware was actually just a DSP at the ISP end. The big difference was before 56k modems, we had multiple analog lines coming into the ISP. We had to upgrade to digital service (DS1 or ISDN PRI) and break out the 64k digital channels to separate DSPs.
The economical way to do that was integrated RAS systems like the Livingston Portmaster, Cisco 5x00 seriers, or Ascend Max. Those would take the aggregated digital line, break out the channels, hold multiple DSPs on multiple boards, and have an Ethernet (or sometimes another DS1 or DS3 for more direct uplink) with all those parts communicating inside the same chassis. In theory, though, you could break out the line in one piece of hardware and then have a bunch of firmware modems.
Yeah 28k sounds more closer to what I got when things were going well. I also forget if they were tracking in lower case 'k' (x1000) or upper case 'K' (x1024) units/s which obviously has an effect as well.
The lower case "k" vs upper case "K" is an abomination. The official notation is lower case "k" for 1000 and lower case "ki" for 1024. It's an abomination too, but it's the correct abomination.
That's a newer representation, mostly because storage companies always (mis)represented their storage... I don't think any ISPs really misrepresent k/K in kilo bits/bytes
Line speed is always base 10. I think everything except RAM (memory, caches etc.) is base 10 really.