Re: Digital Fibre Future
"Yes,all exchanges were digital since the mid 1980's,"
Sorry but that probably should be "all _new_ exchanges were digital since the mid 1980's".
In Europe development on digital exchanges started in the early 1970s when phone companies were hyped about computer powered switches. The only country I know of that saw significant use of those were the USA. The idea was that once you have such a system running, you could just replace the analogue switching matrix with something digital, and you get a completely digital system once that was more economical.
What they didn't take into account were the advances in microelectronics. While back in the early 1970s it was perfectly normal to have a computer with ferrite core memory, it was ridiculously outdated by the early 1980s when development was done. The result was that large parts of those switches were re-developed, based on microcomputers. Those switches then were completely digital and gradually came to service in the 2nd half of the 1980s.
Here's a commercial for a 1970s style analogue computerized switching system:
Ohh and here's a BT film about their development of ISDN switches
There's even a 1984 Japaneese childrens programme about I(S)DN. Here's the German dub of it: