Show that the FIFO-ordered multicast algorithm does not work for overlapping groups, by considering two messages sent from the same source to two overlapping groups, and considering a process in the intersection of those groups. Adapt the protocol to work for this case. Hint: processes should include with their messages the latest sequence numbers of messages sent to all groups
What will be an ideal response?
Let p send a message m1 with group-specific sequence number 1 to group g1 and a message m2 with group- specific sequence number 1 to group g2. (The sequence numbers are independent, hence it is possible for two messages to have the same sequence number.) Now consider process q in the intersection of g1 and g2. How is q to order m1 and m2? It has no information to determine which should be delivered first.
The solution is for the sender p to include with its message the latest sequence numbers for each group that it sends to. Thus if p sent m1 before m2, m1 would include
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Answer the following statement true (T) or false (F)