FSK modulator/demodulator

I need a frequency shift keying (FSK) modulator and demodulator. The modulator is supposed to be able to receive data and modulate them to generate and amplify an FSK waveform, ready to be transmitted out. The demodulator is supposed to be able the detect the reception of the transmitted FSK waveform, demodulate it and correctly recover the transmitted data and save them. The two FSK frequencies f0 and f1 that represent the binary data 0 and 1, respectively, are less than 20 kHz, and must be adjustable (changeable) by the user. All required components of a functional FSK modulator/demodulator for synchronization, detection, out-of-band noise rejection, ..., must be included. Thank you.