Dataflex modems and REN numbers
BT specify that for any single line the REN should equal four. This is
achieved by adding up the REN numbers that are attached to all BT approved equipment. For
example, a standard phone has a REN of 1, some fax machines can be 1 or
even 2, ansaphones are usually 1. This REN is part of the BABT approval
procedure.
The Dataflex modem has a REN of 1 and if you plug in a standard phone to
the socket on the rear of the modem to allow pass through, logically the two REN numbers
are added together to get 2. However the actual REN of this system is 2.5.
Coupled with this is the fact that BT specify their lines have a maximum
capacity of a REN of 4. The line may however only be able to support anything from REN2 to
REN5. If a customer has the Dataflex modem and telephone connected and another phone on
another extension (total REN 3.5) then a problem can possibly arise.
Another complication is that this only applies to BT fitted extensions.
If the customer has purchased a DIY extension kit then this also adds to the REN number,
as the DIY extensions are plug in via a double plug and the BT fitted are hard wired to
the rear of the BT sockets.
The only real cure is to have BT installed extensions and/or a dedicated
fax line.
To diagnose this problem, try disconnecting all other extensions from
the system and connecting the Dataflex modem to the main BT line box. Also it is possible
to have BT check the telephone line by calling the BT engineers. |
