Explanation:

OTT refers to a service that is provided on top of the internet service.
For e.g. you may use the FB Messenger calling feature on an internet network provided by Vodafone. But, as of now, the ISP Vodafone is not concerned with how you use its internet, even if those calls made from FB may reduce its potential revenue.
There are proposals to regulate OTTs after the telecom companies lobbied.
TRAI also released a consultation paper in 2015 on OTT regulatory framework. Some sources confirm that TRAI believes that regulating OTTs is not needed, it has in fact contributed to ISP’s revenues.