The bandwidth of the communication link W=6kHz; using QAM modulation technique with 4 phases, each phase having 4 amplitudes, the number of signal states *** is 4; 44=16. In the absence of noise, the maximum data transfer rate for this communication link can be obtained according to the Nyquist criterion i.e., Cl. : 2W109, N: 2x6x103 xl092 16=12x103 x4=48x103 bps=48kbps.

So the maximum data transfer rate of the communication link is 48Kbps