posting periods in material management

hi mm gurus,

i m fico guy, i need some help form ur side. the t.c. MMPV is closing the posting periods in MM is it right, then what is OMSY? as per as my knowledge in MM we have a chance to open only 2 periods, in OMSY the periods belogs open periods? or closed Perids?

my question in OMSY the periods belongs open or closed?