This Recommendation describes the general requirements and architecture of multiple-wavelength passive optical network (PON) systems. It specifies the mechanism of wavelength assignment@ wavelength tuning and wavelength maintenance in multiple-wavelength PON systems. The functionalities of wavelength resource management and wavelength channel performance monitoring and supervision are also included within the scope of this Recommendation. The specifications in this Recommendation can be applied to various types of multiple-wavelength PON systems such as: ? a stack of several TDM PON systems in a single ODN@ realized by assigning different wavelengths to each TDM PON system@ where wavelength tunable devices may be employed in the transceivers@ ? a TDM PON enhanced by dynamic or semi-dynamic wavelength tuning to allow traffic load balancing@ selective OLT-port sleep@ etc.@ ? a WDM PON in which ONUs do not share wavelengths for offering logical point to point connectivity@ ? a hybrid scheme that combines these or other options. This Recommendation considers the following three classes as the tunability of ONU: fixed@ electrically controlled and optically controlled. This Recommendation considers the following three classes as the wavelength tuning speed: ? slow ( 25 ms to 1 s)@ ? middle (10 ?? to 25 ms)@ ? fast (< 10 ??). This Recommendation includes specification of the functions necessary: ? to initiate the ONU discovery process@ and recognize new ONUs on the PON and their tunability in a way that does not disrupt existing traffic@ ? to assign a newly recognized ONU to an initial operating wavelength set@ both upstream and downstream@ ? to reassign an ONU's operating wavelength set during operation. Not every OLT@ nor every ONU@ need to implement all of these functions. The annex and appendix of this Recommendation provide specific implementations of MW-PON technologies in several systems.