Dear Bhaskar,
I may add, as you are aware, many employers in organised sector generally follow gross monthly salary broken into various components such as basic, other allowances like FDA+VDA, HRA, conveyance allowance, medical allowance, LTA etc. plus other fringe benefits. There are also some employers who doesn't break but keep a consolidated pattern which used to be more than the minimum wages fixed by the respective state govts under the Minimum Wages Act. In this case hike in Gr.salary is given which may not be in a uniform pattern across the board. Whereas those who follow a HR Remuneration policy which provides a set pattern comprising Basic pay plus other allowances can grant periodical increases both in basic as well as in DA and other allowances. Such employers who links their DA components with all India Whole sale/consumer price indices, mostly in organised sector, normally implement increases/decreases in DA commensurate with movement in indices published by GoI from time to time, may be either quarterly or half yearly basis. Therefore if your remuneration policy especially w.r.t. to DA thus linked to price indices you have to follow the same. If you have none, general increase in whole some salary will suffice.