How are trail commissions calculated

I want to know whether trail commission paid to an agent or distributor is calculated based on entry date NAV or year closing date NAV or exit date, whichever is earlier. Because in case it is calculated on year closing date NAV or exit date, then that means the trail commission is paid on the earning or increase over a period of time. What is the limit to define a fund as a debt fund and an equity fund. Debt fund invests 75 per cent of its corpus in debt instruments or 65 per cent?
-Kamal Garg

This article was originally published on May 20, 2013.