I makes sense that if we are integrating BNET on mk1a then we should also integrate it on other aircrafts as well then only link can be created between them.But can't drdo SDR be interconnected with BNET?
Yes, that can be done. BNET has been made to be able to communicate with any other system. For example, I may have a Vodafone connection and you may have Airtel, both networks built by different companies, but both can interact almost seamlessly with each other since they are built on standard protocols.
But it won't be as efficient. That's why all these companies bicker amongst themselves when it comes to interconnection, while offering good deals for people communicating within their own network, like free Vodafone to Vodafone calls/sms etc.
Rigt now I don't know how realistic it is for DRDO's SDR to be used on IAF jets, but eventually, we will need all our stuff to be integrated with each other using one common comm system. And I'm talking about everything aircraft, tanks, ships, soldiers, everything. We will likely have to introduce quantum communications by then as well.
For now, IA and IN will use indigenous systems, while IAF will use the Israeli BNET.