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Basically, I know that Unicast is one to one, Multicast is one to many (the ones that requested the data) and Broadcast is one to all (whether they want the data or not).

In unicast, a data is duplicated and sent one by one by the transmitter to all the receivers that need it. Bandwidth usage here is simply equal to data size * number of receivers, right ?

But how does that work for multicast and broadcast transmissions ? I understood that it is simpler (and more cost effective) for the transmitter that has to send the data just once to the switch (no matter how many receivers). Then the switch takes care of it by forwarding the data to many (multicast) or to all (broadcast). But in the end, the bandwidth usage will increase with the number of receivers too. That means (as before) multiplying the data size by the number of receivers, right ?

For example, is the bandwidth usage of 100 unicast transmissions different from 1 broadcast (or multicast) transmission to 100 receivers ? If so, what’s the trick ?

Many thanks for your time

Jo.
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  • Bandwidth is reduced from the sender, when using multicast or broadcast. The sender only has to send a single copy of the data. Bandwidth on the side of the receiver is of course still the same... everybody has to receive that data. The copying of the data is left up to the network gear. – Brad Dec 12 '22 at 08:14
  • Broadcast is practically deprecated. It is a security risk, and it interrupts every host on the LAN, including routers, printers, etc. that have no interest in the data. IPv6 has eliminated broadcast, so an application that uses broadcast cannot be ported to IPv6. Also, broadcast cannot be routed. Multicast can be routed, but multicast routing is very different than unicast routing. Unicast routing has a single destination and it can be deterministically routed, but multicast has no specific destination, so routing multicast is about not sending it where it is not wanted. – Ron Maupin Dec 12 '22 at 15:42

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