understand multicast and retransmission
Solution
Multicast is group communication where data transmission isaddressed to a group of destination computers simultaneously.Multicast can be one-to-many or many-to-many distribution.Multicastshould not be confused with physical layer point-to-multipointcommunication.
Retransmission, essentially identical with Automatic repeatrequest (ARQ), is the resending of packets which have been eitherdamaged or lost. Retransmission is one of the basic mechanisms usedby protocolsoperating over a packet switched computer network toprovide reliable communication (such as that provided by a reliablebyte stream, for example TCP).