Explain whether the algorithm for reliable multicast over IP multicast works for open as well as closed groups. Given any algorithm for closed groups, how, simply, can we derive an algorithm for open groups?

What will be an ideal response?

In the case of an open group, senders are not necessarily members of the group. In the limiting case, no member sends messages to the group. In that case, there are no opportunities to piggyback information on top of the individual sequence number that any sender keeps for the group. However, a member will be able to
detect a missing IP multicast message when it receives another message from the same sender. The protocol will still operate correctly but with reduced efficiency compared to the case of a closed group: it may take longer to detect a missing message.
In general, an open group algorithm can be obtained by considering the group to be closed and arranging for senders outside that group to pick a member of the group and unicast its message to it. The group member then multicasts it on the sender’s behalf.