In this paper a simultaneous transmission of a 10 Gbps RZ-DPSK data signal for downstream as well as for upstream is proposed and successfully simulated. An OCS (Optical Carrier Suppression) scheme for generation of second order dual side-band optical carrier is utilized by quadrupling a 10 GHz clockfrequency with a 10 GHz LN-MZM (Lithium-Niobate Mach-Zehnder-Modulator). The upper side second order band is used to generate a RZ-DPSK (Return to Zero-Differential Phase Shift Keying) data signal at the OLT (Optical Line Terminal). At the receiving ONU (Optical Network Unit) 50 km away from the OLT the unmodulated lower side second order band coupled with the downlink transmitted signal is utilized for the uplink modulation of 10 Gbps data in RZ-DPSK format. The simulation results show that the performance of the single-tone RZ-DPSK data modulation format is a suitable choice for the WDMPON (Wavelength Division Multiplexing-Passive Optical Network) link with a transmission span of 50 km. The proposed architecture eliminates the need of any pulse carver and mid-span power amplifiers along with the requirement of any power splitting device used in the ONU for colorless uplink transmission. In this scheme, high data rate transmission over long distance is achieved. This scheme merges the boundaries of local access networks and MAN (Metropolitan Area Networks). The proposed scheme is a highly robust, cost effective, backward compatible as well as future proof WDM-PON architecture.