CS454 Assignment 1
Fall 2020
Due: 21 Oct 2020 (5:00pm)
Appeal deadline: within 1 week of return
Question 1 (20%) What factors affect the response time of a client (application) that accesses
data managed by a remote server?
Question 2 (15%) If a client and a server are placed far apart, we may see network latency
dominating overall performance. How can we tackle this problem?
Question 3 (20%) Identify the main benefits and drawbacks of the following architectures:
1. Client–server
2. Unstructured Peer-to-Peer
Question 4 (20%) Assume n computers are interconnected and the availability of every computer
is needed to maintain a distributed service, and each of these computers has a probability
p (0 ≤ p ≤ 1) of failing at any time.
1. What is the probability ps that the service will not be available at any time, assuming
that no other components in the distributed system will fail? Express ps as a mathe-
matical function of n and p?
2. Based on your answer for part (1), what is the probability ps when computing is not
distributed, i.e., for the case where n = 1?
3. Based on your answer for part (1), use p = 0.2 and n = 3 to compute probability ps.
How does this probability compare with the failure probability if the same computing is
performed on only one computer?
4. Now assume that the service requires only one of the three computers with the other
two computers serving as backups (that is, any of the three computers is capable of
providing the service). What is the probability that the service will not be available at
anytime, assuming that no other components in the distributed system will fail? How
does the failure probability of this system compare with the failure probability if the
same computing is performed on one computer only?
Question 5 (25%) Are there advantages of using synchronous RPC over asynchronous RPC? If
so, describe them. If not, provide an explanation of why not.
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