(a) Total order and causal order are two properties that multicast messages can satisfy.
I. Explain the meaning of these two properties.
II. Use an example to show why total order is important for some applications.
(b) Assume that a discussion forum has been replicated on multiple sites. Each user connects to one of the sites to read/submit messages. A submitted message needs to be multicast to all the sites. It is required that a message, say m, can only be made available to a user if all the messages that m casually depends on have been made available to the user.
I. Outline a multicast algorithm that satisfies the above requirements.
II. You should briefly describe the basic principles of your algorithm and how your algorithm works.