  Observations of the HI 21cm transition line promises to be an important probe
into the cosmic dark ages and epoch of reionization. One of the challenges for
the detection of this signal is the accuracy of the foreground source removal.
This paper investigates the extragalactic point source contamination and how
accurately the bright sources ($\gtrsim 1$ ~Jy) should be removed in order to
reach the desired RMS noise and be able to detect the 21cm transition line.
Here, we consider position and flux errors in the global sky-model for these
bright sources as well as the frequency independent residual calibration
errors. The synthesized beam is the only frequency dependent term included
here. This work determines the level of accuracy for the calibration and source
removal schemes and puts forward constraints for the design of the cosmic
reionization data reduction scheme for the upcoming low frequency arrays like
MWA,PAPER, etc. We show that in order to detect the reionization signal the
bright sources need to be removed from the data-sets with a positional accuracy
of $\sim 0.1$ arc-second. Our results also demonstrate that the efficient
foreground source removal strategies can only tolerate a frequency independent
antenna based mean residual calibration error of $\lesssim 0.2 %$ in amplitude
or $\lesssim 0.2$ degree in phase, if they are constant over each days of
observations (6 hours). In future papers we will extend this analysis to the
power spectral domain and also include the frequency dependent calibration
errors and direction dependent errors (ionosphere, primary beam, etc).
