So there can following ways by which Tata Sky is providing these offers
1st is simple, they can adjust actual pack price in the NCF they earn thus giving share to broadcasters while reducing their profit margin
2nd one is the interesting one, though i have doubts on how it exactly works. In first scenario, there could b a special arrangements b/w concerned broadcasters and operators that broadcasters give these channels free to operator for 1 month and as their viewrship increases along with ad revenue, they somehow mention part of ad revenue as broadcaster bouquet fee from operators in record and pass on operator share thru carriage fee or ads on their home channels. Though this can b tricky as TRAI can catch hold of it. Second scenario is more feasible where operator pays broadcaster share of bouquet price from NCF earned while broadcaster earns more from ad revenue from increased viewership and passes on benefits to operator thru ads or carriage fee
I also notice that sometimes certain operators offer their sister broadcaster channels at heavy discount, though this is allowed under rules but then i feel rival broadcaster channels get left out... Again in this too broadcasters can give operators part of ad revenue earned thru ads on home channels or some channel carriage fee