QUESTION 1
(a) (i) Give an example of a URL.
(ii) List the three main components of a URL, stating how their boundaries are denoted and illustrating each one from your example.
(iii) To what extent is a URL location transparent?
(b) Suppose that the operations of a BLOB object are separated into two categories - public operations that are available to all users and protected operations that are available only to certain named users.
(i) State all of the problems involved in ensuring that only the named users can use a protected operation
(ii) Supposing that access to a protected operation provides information that should not be revealed to all users, what further problems arise?
(c) Explain the two approaches to packet delivery by the network layer in Distributed Systems.
(d) Describe the three fundamental models of Distributed Systems
(e) Define latency, bandwidth and jitter.
QUESTION 2
(a) How does the client-server architecture of Web applications involve the partitioning and/or replication (or caching) of data amongst servers?
(b) With the use of an appropriate example, illustrate how Distributed Systems masks failures for successful completion of invocations
(c) Distinguish between buffering and caching
(d) The term reliable communication is defined in terms of validity and integrity.
(i) Define validity
(ii) Define integrity
(iii) Give two sources which can be threats to the validity and integrity of the messages
QUESTION 3
(a) Explain four mechanisms for security in Distributed Systems.
(b) Describe the OSI Protocol.
(c) A client sends a 200 byte request message to a service, which produces a response containing 5000 bytes. Estimate the total time to complete the request in each of the following cases, with the performance assumptions listed below
(i) Using connectionless (datagram) communication (for example, UDP).
(ii) Using connection-oriented communication (for example, TCP).
(iii) The server process is in the same machine as the client.
[Latency per packet (local or remote, incurred on both send and receive): 5 milliseconds
Connection setup time (TCP only):5 milliseconds
Data transfer rate: 10 megabits per second
MTU: 1000 bytes
Server request processing time: 2 milliseconds
Assume that the network is lightly loaded.]