FSK Demodulation (help urgently needed)

Hi

 I am trying to Extract Caller ID from FSK v.23 Encoded CLI Packet which
has been stored in audio format in pc. To demdulate FSK i am using two
Bandpass Filters centered at Mark and Space Frequency. According to FSK
V.23
1300 hz is frequency for mark(1)
2100 hz is frequency for spcae(0)
1200 is baud rate
my sample rate is 8000/s
i have 1/1200=833 us to check for the new arrival. In 833 ua i have
1300/1200=1.08 cycles of mark and 2100/1200=1.72 cycles of space. 
The problem is i have no idea how to embedd a clock in this scenario. I
mean what would be the frequency or timeperiod of the clock to ensure
accurate decoding.

Thanks for your help in advance