Running 56kbps modem through ISDN TA

[ranting]

A friend of mine called with a problem that I don't quite know what to make of: he knows this couple that wants to have ISDN at home for the comfort of two phone lines.
In order to get both their Macs online, they want to run a 56 kbps modem through the ISDN TA.
I've heard that this is feasible, but can cause problems.
Anyone have any experiences ?
(I suggested going for a Zyxel 201 ISDN router

 

[Moonbender]

It is possible to connect a analog modem to the same device which you can plug your analog phones in.
However, depending on the quality of that device (is that a ISDN TA? I don't know the name in English ...), you won't reach full speed, it could for instance be capped at 28800 baud. I don't know if it is (even theoretically) possible to reach the full 56k speed.
I tested it with the internal 56 kbaud modem of my mother's laptop, and it connected at 33.6 kbaud.

A real ISDN 'modem' (of course it's not actually a modem) is far better of course, many of the TAs (if a TA is what I think it is ) have a ISDN modem built-in, at least mine has and it works fine, although a external device hurts the pings quite a bit.