What is the Average eRPM or eCPM for text link Ad Networks for India Based Websites

I have been blogging for last few years and during my initial days I started with text link ads of different networks but I have stopped the use of these networks after drastic fall in my earnings. I wonder if there is correction in the earnings from these networks.

There are many new bloggers who might not believe that I used to earn around $2- $4 eCPM for India based visitors through text link ads.

When I stopped using the text link ads in January 2012 after continuous use for about 3 years the eCPM had dropped to $0.1 to $0.25 for same type of visitors. I don't know what happened to these ad networks as the fall in the earnings was beyond my understanding of the online advertising business as Google Adsense has been quite regular with its earning without much fluctuation.
However, I still see that websites are using the text link ads of different networks. I just want to know if the earning potential of these text link networks have increased or these websites are simply wasting their ad space. I also want to know if the eCPM is deliberately decreased by the ad networks for its older publishers.