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cop5615fa10quiz3Key - order at all receivers 2 Consider...

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Quiz 3 Key COP 5615 Fall 2010 1. In group communication/multicast, what are the delivery requirements for (a) FIFO order? (b) Causal order? (c) Total order? 2. Give a simple example of message delivery that (a) satisfies FIFO order but not causal order; (b) satisfies causal order but not total order. KEY 1. The requirements are: (a) All messages from the same source are delivered in the order that source sent them. (b) all messages that could have affected (i.e., that 'came before”) a given message M are delivered before M is delivered. (c) all messages are delivered in causal order, and are delivered in the same
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Unformatted text preview: order at all receivers. 2. Consider three processes, P1, P2, and P3. P1 broadcasts a message M1 to the other two, and P2 broadcasts M2 to the other two before it receives M1. Then P2 broadcasts M3 to the other two after it has received M1. Causal order requires that M1 be delivered before M3, since M3 may have been affected by M1, and that M2 be delivered before M3. FIFO order only requires that M2 be delivered before M3. (a) P3 delivers M2, then M3, then M1. (b) P2 delivers M2, then M1, then M3; but P1 delivers M1, then M2, then M3....
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