Hello,
There are four standards as follow:
ITU-T G.987.1: defines overall requirements in the next generation PON system.
ITU-T G.987.2: provides physical medium dependent (PMD) specifications at the physical layer in the next generation PON system
ITU-T G.987.3: provides GPON transmission convergence (GTC) specifications at the convergence layer in the next generation PON system.
ITU-T G.988: provides optical network terminal management and control interface (OMCI) specifications in the next generation PON system
Thanks