William Waites via 44Net je 12. 10. 20 ob 10:04 napisal:
How can the native part scale (beyoned 44Net)? We can't have zillions of join/leave messages percolating all the way up the tree because the load resulting from processing these would become unmanageable. In the limit, each multicast group containing two participants, we've just recreated unicast with a far more expensive routing protocol. But neither can we have all sessions carried in the core (or can we? are we able to overprovision like that? maybe if we reengineer the content distribution networks to do this... perhaps they do it themselves already). Anyways, that's the basic trade-off (regardless of protocol choice or acronym flavour). A partial solution is to also have a notion of geographic scope.
Multicast happens only on local subnet. But it can be extended to other subnets via unicast by help of PIM protocol (Protocol Independent Multicast).
PIM supports two modes: dense and sparse mode. In dense mode a sender floods the whole network until receivers explicitly say no (prune). In sparse mode there is one Rendezvous Point (RP) where receivers ask to join the sender stream.
RP does a coordination so that sender streams via unicast directly to the receiver's subnet router, which finally multicasts to that subnet. This way the multicast traffic is reduced on the whole network to a minimum.
RP router is a single point of failure, so there are more candidate RP routers. And to complicate matter a bit more, there are also Bootstrap routers (BR) to help discovering the RP.
Mikrotik is the only one among cheaper gear to have a PIM (only Sparse mode) implementation. It is a bit clumsy but with a few tweaks it is (from my experience so far) manageable.
73, Janko S57NK
Anyways, just some thoughts.
73s VE0HAK