Hi Sudheer
You need software component EA-HR_MSS 1.0 for MSS Add-on delivery in the back-end ECC system - Im not sure this is available for EHP3 though ? - EA-HR_MSS 1.0 was delivered with EHP5 as far as I am aware - as standard MSS only became Portal Agnostic from EHP5
It might be possible to install it on earlier releases but I've not encountered any customers who have done it
Best wishes
Stuart