[Gllug] ADSL upload speeds

Chris Bell chrisbell at overview.demon.co.uk
Mon Jun 27 06:56:36 UTC 2005

On Mon 27 Jun, Robert Newson wrote:

> I don't remember that far back, but I do remember it being illegal (still?) 
> to plug a non BT Approved phone/modem into the BT system - ie if the device 
> had a Green Triangle it was approved and could be connected to the BT 
> network; if it had a Red Circle it was not approved and so couldn't be 
> connected.  (I never understood the point of that as unapproved devices 
> couldn't be connected directly, or indirectly - was there a way to use them 
> outside the BT system?)
   It used to be illegal to run a wire across a boundary between adjacent
properties without going through the Post Office, (before BT), although Hull
council ran their own independant system, but now there is nothing to stop
you owning and running your own private exchange.
   Modern private branch exchanges can use either analogue, digital, or both
types of phone, with different connections through the current standard
plug. The old Post Office phones used an older concentric multiple-ring
connector, twin Post Office jacks, or were permanently wired, and had low
impedance ringers, connected in series using difficult-to-obtain additional
switches operated by lifting the handset from the rest.
   Non-UK phones came with FCC68/RJ11 connectors suitable for use in
America, modern phones come with high impedance ringer circuits, to be
connected in parallel, or use tone detection and powered sounders.
   Approved phones would work using the line volts and without local power,
so are suitable for emergency use, while ISDN, some digital, and VOIP, may
fail without standby battery power. Public telephone exchanges usually have
huge standby batteries and emergency power supplies.
   Then there are phones like the Tele-F with internal 1.5 volt battery and
hand operated ringer (modern versions have a transistor operated ringer) to
call the exchange.

Chris Bell

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