Hi Seema,
You are correct, the notice period differs with every position. Every position has different authority, lines of communication & levels of responsibility. The higher you go on the above parameters the more important is your position within the organisation. There is no difference as per functions but notice period differs with positions. In my organisation the notice period for VP & above level is 3 months, for the Middle level management like managerial positions is 2 months and the rest is 1 month. This is framed bcoz the exit of higher end individuals affects the working of the organization directly/indirectly. Secvondly, it is easier to replace people at first level & gets all the more difficult as we go higher in the ladder. Since a lot of issues like confidentiality, trust, values etc are to be checked with the people sitting on the top management. It gets more difficult although not difficult to get the right candidate for that position.
Regards,
Pooja