a$)$ i$.$ Define Distributed system and give two examples.

$[35$ marks$]$

ii$.$ Define the publish$/$subscribe communication paradigm.

iii. Define access right. Explain how access right is used to ensure security in a distributed system.

b$)$ Consider the Chord system as shown in Figure $1,$ please answer the following questions:

i$.$ Please provide the finger tables for nodes $1,5,10,13,$ and $17.$

ii$.$ Please show how to resolve $k=19$ from node $1$ using these finger tables.

c$)$ i$.$ With the aid of diagrams distinguish between a vertical distribution and a horizontal distribution in multitiered architecture?

ii$.$ The terms loosely$-$coupled system and tightly$-$coupled system are often used to described distributed computer systems. What is the different between them?

Question Two

$[35$ marks$]$

a$)$ i$.$ Describe with an example the major difference between call$-$by$-$value and call$-$by$-$reference.

ii$.$ How is RPC different from LPC $($local procedure call$)?$

iii. Describe how RPC ensures transparency of operation in inter$-$process communication of a distributed system?

iv$.$ Explain idempotent process. How is idempotency achieved in a request$-$reply protocol?

b$)$ Consider two communication services for use in asynchronous distributed systems. In service $A,$ messages may be lost, duplicated, or delayed and checksums apply only to headers. In service $B,$ messages may be lost, delayed, or delivered too fast for the recipient to handle them, but those that are delivered arrive with the correct contents:

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i$.$ Describe the classes of failure exhibited by each service.

ii$.$ Classify their failures according to their effects on the properties of validity and integrity.

iii. Can service $B$ be described as a reliable communication service?