"USRP2+XCVR2450 TxGain / RxGain meaning"‏

Hello,

I’m using the USRP2 board with the daughterboard XCVR2450. As far as I
know,
the output power of the XCVR2450 is 100mW (20dBm), but I don’t
understand
the meaning of the TxGain and RxGain factor when I use for example
tunnel.py. I have been able to identify that the Tx Gain varies between
0<Tx
Gain<30 and the Rx Gain between 0< Rx Gain <92.

Thank you for your help!
Regards,
Baldo