Recommendation ITU-T G.984.1 defines the maximum differential distance between any two ONUs on the passive optical network (PON) as 20 km and the GPON logical reach has been defined as 60 km. However, based on practical deployment experience, it has been found that a differential distance of 40 km ranging from 0 to 40 km, 20 to 60 km, or distances in between allows significant flexibility in PON deployment and offers many benefits including the ability to serve sparsely populated areas in an efficient manner. The present Recommendation describes the necessary requirements for GPON to support the differential distance of 40 km.