Define Frequency and Total period.

The frequency is the time period after the start date when you want SIP orders placed in your account. The order must be executed at least once.

These are the frequencies and maximum periods that are allowed.
 

Frequency	Maximum allowed period
Daily	500
Weekly	100
Fortnightly	50
Monthly	24

You can take an example. If you have put a SIP Instruction to buy 100 shares of ONGC at a Monthly' frequency for a total of 2 months, with a start date of 12-07-2011 Securities will place two orders for this SIP. The first order will be placed on the Start date, and the second order in the month following the start date.