Problem 2: DS Architecture Consider a multi-tiered client-server architecture co

Question

Problem 2: DS Architecture

Consider a multi-tiered client-server architecture consisting of a chain of processes P1, P2, …, Pn. Process Pi is a client of Pi+1 , and Pi will return a reply to Pi-1   only after Pi receives the reply from Pi+1.

(a)   Please provide arguments for adopting this multi-tiered client-server architecture in a DS design. Briefly explain your answer. (Hint: your answer me be based on the distributed system design goals, including but not limited to: scalability, reliability, security, application’s demand, etc.)

(b) Please provide arguments against adopting this multi-tiered client-server architecture. Briefly explain your answer. (Hint: Again, your answer me be based on the distributed system design goals, including but not limited to: scalability, reliability, security, application’s demand, etc.)

Explanation / Answer

When we consider the goals of distributed systems scalability ,reliabilty ,security ,performance and applications demands are very important.The scalability of a distributed system is measured by along 3 different dimensions 1.size,2.geographical,3.administrative.The size defines the number of users/processes .The maximum distance between the participants is denotes the geographical dimension.And finally administrative stands for the administrative domains.Here the size of process is p1, to pn.And the geographical dimension denotes the distance between process pi to pi+1 and so on.

while considering the next goal of distributed systems ,the reliability it is essential.it depends on the increasing number of users /processes/organizations.For ensuring realiability we have to maximize the avaliabilty that means number of time the system is usable.And need to maintain consistency and security.Need to cover all failures,and to be recovered from errors.

Another important goal of distributed systems are their performance. while considering the above client-server architechture of processes p1,p2..pn.the performance will be less for large number of n.The problem occured in the performance is each communication between two successive layers is ,in principle between two different machines.Gradually the performance between p1 and p2 may also be determined by n-2 request reply interactions between the other layers.The next problem is that if one machine in the chain perform poorly or uncreachable for some times ,then it will decrease the performance of highest level.

Another importent goal of distributed system is the security .By providing various security mechanisms like Encryption,Authentication,Authorization,Auditing we can ensure the security.While tailing about the applications demand in a distributed systems all the resources should easily accessible .The main goal is to make it easy for the users (and applications) to access remote resources and to share them in a controlled and effient way.In the above architechture recourse sharing is difficult in between pi+1 to pi and pi-1 and so on.

Another goal of distribution systems is distribution transparency here the goal is to hide the fact that its processes and resources are physically distributed across multiple computers system should be transparent.Different forms of transparency in a distributed system is Access,Location,Migration,Relocation,Replication,Concurrency and failure.

opennes is the other goal of distributed systems.Here the goal is to offer services according standard rules that describe the syntax and semantics of those services.

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