Afternoon RONSKI

I remember and used Acoustic Couplers at 110 Baud, approximately 110 bps.

1200/75 Baud Down/Up was an improvement, then 300/300.

56 Kbps, running typically about 44 Kbps - WOW !!

Also in the early days of Mobile Phones, three were delivered to our company, as three separate sub-assemblies each, no instructions.

I tackled putting together the first, eventually turned out that the sub-assemblies were linked, so had to dis-assemble and re-assemble with the related parts.

Got it working on Voice, then assembled the other two.

They were also supposed to handle FAX and Dial-Up.

Eventually the supplier mentioned that these were separate numbers, so three phones, nine numbers, each needing individual registering and authorisation!

The first real use was from Portugal to Scotland, so another learning cycle.

I remember 56k modems, and people saying you can't go faster it's just not possible

i think they were right, has anyone bettered 56k using audio frequencies on a voice line ?

At the time 128k was available via ISDN, but that was A Different Thing (tm) just like xDSL is.

Oh the joys of a teletype on an acoustic coupler in Manchester for driving online programming at a London bureau.

In reply to a post by yarwell:

I remember 56k modems, and people saying you can't go faster it's just not possible

i think they were right, has anyone bettered 56k using audio frequencies on a voice line ?

At the time 128k was available via ISDN, but that was A Different Thing (tm) just like xDSL is.

Within the PSTN (ie the switched telephony network), the digital exchanges that were installed in the 80's all converted voice signals to digital. The digital signal was 8 bits, sampled at 8kHz, resulting in 64,000 bps. This is the G.711 standard - and the entire digital switching technology was focussed on switching lumps of 64Kbps.

A voice-line modem that used the *switched* network couldn't hope to carry any more than that 64Kbps, ever - the data would be lost in the sampling - and must be quite smart to get over 32Kbps.

The basic rate ISDN specs (2B+D) carried 2 of these voice channels, which is where the 128Kbps comes from.

And yes - the primary rate ISDN circuits, carrying 30 voice channels (total, including overhead, 2Mbps) were fairly standard fare over copper in the 80's; I only ever came across it in coax, but it could be carried over a 4-wire copper interface (ie 2 pairs).

The techniques behind ADSL and VDSL have been around for a long, long time. There were systems providing, what at the time were, very high bandwidth connections in the 1980s, but the problem was the size of the terminal equipment and both ends. Most of it was hardware rather than software driven. The belief now is that the limits of copper pairs are now being hit or are very close. Without changing te laws of physics, getting a certain frequency signal any further along a copper pair is unlikely.