The passive optical network has been shown to be a cost effective method of introducing fibre to the access network. However, the expected increase in demand for broadband services will inevitably mean that upgrades in capacity will be needed. Wavelength division multiplexing offers an alternative to increasing the bit rate. Two broad strategies exist for the implementation of multiple wavelengths on passive optical networks (PON), fixed wavelength schemes and dynamic wavelength assignment. Wavelength reallocation at call setup allows a flexible response to changes in network demand. It does not, however, take full advantage of statistical multiplexing and the ATM approach. In order to do so, new protocols need to be developed which combine the allocation of wavelengths and time slots. The approach here shows a method based on wavelength allocation at the frame level. A scheme to reduce cell delay variation recently proposed for single wavelength systems is adopted for WDM and an improvement to it demonstrated.