Midterm Answers

Midterm MIS 642


  1. Explain the goals of a distributed system.
A collection of independent computers that appears to its users as a single coherent system
Goals of Distributed Systems
Connecting resources and users
Distribution transparency
Openness
Scalability

  2. Match the OSI model to the TCP/IP stack.

The TCP/IP architectural model has four layers that approximately match six of the seven layers in the OSI Reference Model. The TCP/IP model does not address the physical layer, which is where hardware devices reside. The next three layers—network interface, internet and (host-to-host) transport—correspond to layers 2, 3 and 4 of the OSI model. The TCP/IP application layer conceptually “blurs” the top three OSI layers. 

  3. Describe 2 architectural Models of distributed systems.

  A. Client server architectures are distributed services which are called on by clients. Servers that provide services are treated differently from clients that use services.  
  * The application is modeled as a set of services that are provided by servers and a set of clients that use these services.
  * Clients know of servers but servers need not know of clients.
  * Clients and servers are logical processes
  * The mapping of processors to processes is not necessarily one to one.

  B. Service-Oriented Architecture (SOA), SOA also generally provides a way for consumers of services, such as web-based applications, to be aware of available SOA-based services. For example, several disparate departments within a company may develop and deploy SOA services in different implementation languages; their respective clients will benefit from a well understood, well defined interface to access them. XML is commonly used for interfacing with SOA services, though this is not required. SOA defines how to integrate widely disparate applications for a world that is Web based and uses multiple implementation platforms. Rather than defining an API, SOA... [continues]

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