In order to sustain India's strong growth rate, Finance Minister P Chidambaram has said that the country requires an investment of $320 billion in infrastructure over the next five years, a large part of which would come from the private sector through the public-private partnership (PPP) model.The Finance Minister said that international and Indian finance companies are joining hands to launch dedicated infrastructure debt and equity funds, and added that "efforts taken by these institutions will bear fruit in the next few weeks.""There are four constraints in attracting investment, which glaringly include weakness in policy and regulatory framework as most of the projects are within the purview of states," Chidambaram said at infrastructure conference organised by the World Bank.There are also a lack of long term market financial instruments to meet equity and debt financing needed by infrastructure projects, he said.Highlighting other constraints, Chidambaram said there was lack of credible and bankable projects and also lack of capacity among public officials and institutions to handle these projects.However, he assured that government is aware of the situation and have opened more sectors for public-private partnership.He said PPP was a great opportunity, which should be translated into win-win proposition.