Been a while since I did ISDN, would have been a pri E1 line (T1 is a US standard) though. 32 x 64kbit channels and 1 x 16kbit. They could dynamically change between voice and data if needed and were pretty cool.
ISDN i assume you mean a bri, 1 x 16kbit and 2 x 64 kbit.
Been years since I done any of this so the above could be wrong.
i have 56k modems in crossfire overclocked to 96k baud