  The purpose of this paper is to provide a multilayer review of the two major
standards in next generation Passive Optical Networks (PONs) and technologies,
the ITU-T 10-Gigabit-capable PON (XG-PON) and the IEEE 10 Gigabit Ethernet PON
(10G-EPON). A study and a discussion on the standards are performed. The main
intention of this paper is to compare XG-PON and 10G-EPON, mainly in terms of
physical and data link layers. The paper answers the question of what are the
common elements and the basic execution differences of the two standards.
Moreover, critical points are raised regarding the Dynamic Bandwidth Allocation
(DBA) schemes of both standards. Special focus is also pointed in the
coexistence of XG-PON and 10G-EPON. Finally, the paper includes a discussion of
open issues and continuing research regarding the two standards.
