Mark Andrews wrote:
>>A real difference between unicast and multicast/broadcast of CSMA/CA
>>wireless link such as 802.11 is that the latter can not be ACKed and
>>is unreliable.
>
>
> Multicast is unreliable, period. This is independent of the
> media being used.
If you assume L4 ack and retransmission, you are right.
However, even at L4, unidirectional UDP unicast is just as reliable
as unidirectional UDP multicast.
At L2, Ethernet multicast is as reliable as Ethernet unicast and
802.11 unicast, because there are CD or ACK and retransmissions.
OTOH, 802.11 multicast with no CD, ACK nor retransmission is a
lot less reliable.
Masataka Ohta
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