Wavelength division multiplexing passive optical networks (WDM PONs) can dynamically offer each end user a unique optical wavelength for data transmission as well as the possibility of wavelength reuse and aggregation, thereby ensuring scalability in bandwidth assignment. In this paper, we propose a new byte size clock (BSC) reservation MAC scheme that not only arbitrates upstream transmission and prevents optical collisions, but also varies bandwidth according to demand and priority, reduces request delay using pre-allocation and delta compression, and handles the addition/reconfiguration of network nodes efficiently. The new access scheme exploits both WDM and TDM to cater for both light and heavy bandwidth requirements and supports both Ethernet and ATM packets without segmenting or aggregating them. Our proposed protocol is not only backward compatible with APON and EPON, but also provides a better utilization of the access link in terms of the throughput and delay. In addition, the amount of pre-allocated bandwidth can be minimized using delta compression, which in turns reduces the latency due to the request and grant mechanism. We analyzed, evaluated, and simulated the performance and practicality of the proposed scheme.