If i set up a modulator at home for ATSC, I can pick what I want displayed and I can pick the RF channel. I would ghave an HDMI input for every stream and I probably should assign it a unique TSID (Transport Stream ID) that's unique for my location.
e.g. A TSID of 1000 might always mean program #3 in California TY station with call letters <WWWW> everywhere in the US.
Just like MAC addresses for the Internet, they are generally unique to make life easy, but in reality only have to be unique over routeable segments. This, you can clone MAC addresses.
You have a MAC address, an Ethernet address and a port # that differentiate a stream of Ethernet traffic.