Didn't get a chance to respond to the multi-casting thing earlier, but that was something we leveraged in the company I worked for that was a Satellite VSP (vertical services provider). This was in addition to the standard ISP internet services provided (with all of the latency-reducing tricks needed to get even mediocre performance).
We used multicast for provide content to endpoints for things like video loops (think store displays, business waiting rooms, educational content, etc...). Basically we'd multicast a video stream across the bird for each customer set. At the endpoint location we provided a cache/playback machine. A typical example was body repair shop: the cash register/POS system used the unicast satellite service for their credit card transactions, the waiting room would play an advertising video loop it had received via multicast the night before.
Multicast requires all of the devices in chain to support it, not just the transmission and end-points. This makes it viable for something like sat service, where you don't have other people's routers and switches in your path. It's a very efficient way to deliver a lot of static data to many endpoints simultaneously.
However that also constrains your set of services. As mentioned above, the nature of web surfing and on-demand media consumption is such that it's hard to do much with that via multicast. It would useful for "live" event channels where everyone is receiving the same event without staggered start times (akin to terrestrial broadcast), and then the endpoint can cache locally for pause/rewind, etc... It also is great for updating stuff: send the same firmware to 5 or 5 million devices so they can update. I could see that being useful for Starlink at some point.
Incidentally, the system we used actually shoved the packet payloads in to what looked like an MPEG DVB frame at the transmit side, as that what the systems in use had originally been designed to handle... the VSAT terminal on the endpoint then unpacked that in to a TCP/IP packet to had to the endpoint device. A hack, unlike the special-purpose transport used by SpaceX that @Cosmacelf refers to, but another example where the protocol traversing the bird is something different than just plain TCP/IP.
We used multicast for provide content to endpoints for things like video loops (think store displays, business waiting rooms, educational content, etc...). Basically we'd multicast a video stream across the bird for each customer set. At the endpoint location we provided a cache/playback machine. A typical example was body repair shop: the cash register/POS system used the unicast satellite service for their credit card transactions, the waiting room would play an advertising video loop it had received via multicast the night before.
Multicast requires all of the devices in chain to support it, not just the transmission and end-points. This makes it viable for something like sat service, where you don't have other people's routers and switches in your path. It's a very efficient way to deliver a lot of static data to many endpoints simultaneously.
However that also constrains your set of services. As mentioned above, the nature of web surfing and on-demand media consumption is such that it's hard to do much with that via multicast. It would useful for "live" event channels where everyone is receiving the same event without staggered start times (akin to terrestrial broadcast), and then the endpoint can cache locally for pause/rewind, etc... It also is great for updating stuff: send the same firmware to 5 or 5 million devices so they can update. I could see that being useful for Starlink at some point.
Incidentally, the system we used actually shoved the packet payloads in to what looked like an MPEG DVB frame at the transmit side, as that what the systems in use had originally been designed to handle... the VSAT terminal on the endpoint then unpacked that in to a TCP/IP packet to had to the endpoint device. A hack, unlike the special-purpose transport used by SpaceX that @Cosmacelf refers to, but another example where the protocol traversing the bird is something different than just plain TCP/IP.