What is the minimum service period for pension eligibility

What is the minimum service period for being eligible for pension? If for some years I have worked in one PSU and in another PSU for some years, will the total number of years worked in earlier PSU be taken into consideration for fixing eligibility years for pension?
27th April 2012 From United States , Cambridge

PF transfer from one employer to another employer- use Form 13 for transfer of your PF . Job change is very normal in these days. So it has become common for everyone to transfer their Provident Fund (PF) to the new employer’s organisations. To do so, there are certain processes to be followed under EPF Act and it can be varied if the employer has their own PF trust for their employees.
Yes, it will be taken into consideraion for fixing he number of years provided you have not withdrawn previous P F accumulated amount / sought for transfer of PF.
9th May 2012 From India , Jhansi