The classic switch is based on 64kbits/s stream. The traditional MSC is based on the classic 64kbits/s stream for Voice connections.
TRAU is used to convert the rate to 64kbits/s. You have to see if your Network is configured for FR/HR/EFR.
Not sure is you have TFO in operation.
Let me know if you need any further inputs.
VBR/ Wallis Dudhnath