[DoubleGlazing]

Back in the late 90s when Ireland was starting to think about digital terrestrial TV a system called DVB-RCT was considered. Basically your receiver could also transmit back to the television transmitter. The system could handle thousands of concurrent connections, albeit each one had very low bandwidth - around 1Kbp/s in peak time.That was considered good enough for very basic interactivity and for authorising PPV purchases etc.In quieter hours or in areas were there were fewer receivers that bandwidth would be much higher, but in reality that would be rare.

In the end the company that the governement selected to start the rollout of DTT went bust and I don't think the system was used anywhere else. The developer of the technology abandoned it in 2006 as other connection methods (broadband/mobile data) were preferred.