(Note virtually all MC apps use UDP.)
To understand MC efficency, we must compare with UC (unicast) and BC (broadcast). First we need some “codified” metrics —
TT = imposing extra Traffic on network, which happens when the same packet is sent multiple times through the same network.
RR = imposing extra processing workload on the Receiver host, because the packet is addressed TO “me” (pretending to be a receiver). If “my” address were not mentioned in the packet, then I would have ignored it without processing.
SS = imposing extra processing workload by the Sender — a relatively low priority.
Now we can contrast MC, UC and BC. Suppose there are 3 receiver hosts to be notified, and 97 other hosts to leave alone, and suppose you send the message via —
UC – TT not RR — sender dispatches 3 copies each addressed to a single host.
BC – RR not TT — every host on the network sees a packet addressed to it though most would process then ignore it, wasting receiver’s time. When CEO sends an announcement email, everyone is in the recipient list.
MC – not RR not TT. However, MC can still flood the network.