This memo provides application‐specific requirements for the Path Computation Element Communication Protocol (PCEP) for the support of Wavelength Switched Optical Networks (WSONs). Lightpath provisioning in WSONs requires a Routing and Wavelength Assignment (RWA) process. From a path computation perspective, wavelength assignment is the process of determining which wavelength can be used on each hop of a path and forms an additional routing constraint to optical light path computation. Requirements for PCEP extensions in support of optical impairments will be addressed in a separate document.