Jurgen thank you for sharing this link.
Now I understood the difference between these two replenishment type.
But still one thing is not clear to me.
In case of Planned replenishment system will ROUND DOWN while in case of Order related replenishment system will ROUND UP to the multiple of minimum replenishment quantity.
How ROUND DOWN and ROUND UP functions and work while replenishing the quantity.
Also what exactly ROUND DOWN and ROUND UP mean in replenishment process .
I know my this question will make you laugh 
pls bear me.
But answer to his question will clear my all doubts.
regards
Srinivas