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COP 4610L: Java Networking Part 1 Page 1 Mark Llewellyn ©COP 4610L: Applications in the EnterpriseSpring 2006Java Networking and the Internet – Part 1COP 4610L: Applications in the EnterpriseSpring 2006Java Networking and the Internet – Part 1School of Electrical Engineering and Computer ScienceUniversity of Central FloridaInstructor : Mark [email protected] 242, 823-2790http://www.cs.ucf.edu/courses/cop4610L/spr2006COP 4610L: Java Networking Part 1 Page 2 Mark Llewellyn ©Distributed Applications in the Enterprise• Distributed applications are currently one of the latest developments of information technology, which began about 50 years ago and is still developing at a very fast pace.• The first electronic computers available in 1940s and 50s were reserved for special applications. Many had military applications such as the encryption and decoding of messages.• The 1960s witnessed the advent of batch processing, in which several users could pass their tasks to the computer operator (the “server”). Once processed, the results were returned to the “client” by the operator. As there was no interactivity at that time, computers were used for primarily numerical applications that required little user input but required a high computational effort.COP 4610L: Java Networking Part 1 Page 3 Mark Llewellyn ©Distributed Applications in the Enterprise (cont.)• With the advent of mainframes, interactive applications came into play. Several users could finally user one computer simultaneously in time-sharing mode. Tasks were no longer completed in sequence as with batch processing, but rather completed in sections.• The next trend, beginning with the introduction of the PC in 1980, was the shift in computing power from the central mainframe to the desktop. Computer performance at levels which were undreamt of previously, was now available to employees directly at their desk. Each user could install their own applications to create an optimally configured work environment. This began theage of the standardized office packages, which enabled office automation to be driven forward considerably.COP 4610L: Java Networking Part 1 Page 4 Mark Llewellyn ©Distributed Applications in the Enterprise (cont.)• Since the 1990s, the trend has shifted increasing from distributed information processing to enterprise computing. • Previously autonomously operating workstations were integrated together with central file, database, and application servers, resulting in huge decentralized clusters., which were used to handle tasks of a more complicated nature. • The defining sentence which characterized this phase coined by Sun Microsystems reads – “The network is the computer.”• What was it that led to this ever increasing greater importance of distributed applications?• There are several reasons commonly cited:COP 4610L: Java Networking Part 1 Page 5 Mark Llewellyn ©Distributed Applications in the Enterprise (cont.)1. The cost of chip manufacturing dropped sharply, enabling cheap mass production of computers.2. Simultaneously, network technologies were developed with higher bandwidths – a necessity for the quick transfer of large amounts of data between several computers.3. Response times became increasingly longer due to the heavy use of large mainframes, resulting in excessive waiting times.4. The availability of a comparable distributed work environment gave rise to the desire for new applications that were not possible in a centralized environment. This development led from the first e-mail applications via the WWW to common use of information by people in completely different places.COP 4610L: Java Networking Part 1 Page 6 Mark Llewellyn ©What is a Distributed System?• While many different definitions of what constitutes a distributed system have been put forth, there is general consensus that there are several central components that a distributed system must contain:– A set of autonomous computers.– A communication network, connecting those computers.– Software which integrates these components with a communication system.COP 4610L: Java Networking Part 1 Page 7 Mark Llewellyn ©What is a Distributed System?Node ANode BNode CNode DMachine limitsUSER Software componentCommunicationCOP 4610L: Java Networking Part 1 Page 8 Mark Llewellyn ©What is a Distributed Application?•A distributed application is an application A, the functionality of which is subdivided into a set of cooperating subcomponents A1, A2, …, Anwith n > 1. The subcomponents Aiare autonomous processing units which can run on different computers and exchange information over the network controlled by coordination software.• There are typically three levels defined for a distributed system:Distributed Computer SystemLevel 1Coordination SoftwareLevel 2Distributed ApplicationsLevel 3COP 4610L: Java Networking Part 1 Page 9 Mark Llewellyn ©What is a Distributed Application? (cont.)• The application on level 3 will ideally “know” nothing of the distribution of the system, as it uses the services of level2, the administration software that takes over the coordination of all the components and hides the complexity from the application.• In turn, level 2 itself uses the available distributed computing environment.As an aside, a more humorous definition of a distributed system was given by Leslie Lamport (the guy who developed LaTex), who defined a distributed system as a system “in which my work is affected by the failure of components, of which I knew nothing previously.”COP 4610L: Java Networking Part 1 Page 10 Mark Llewellyn ©Important Characteristics of Distributed Systems• Based on our simple definition, there are several important characteristics of distributed systems that need a closer look.• All of these characteristics are based on the concept of transparency. • In the context of information technology, the concept of transparency literally means that certain things should be invisible to the user. The manner in which the problem is solved is largely irrelevant to the user.• The following transparency properties play a large role in achieving this result for the user:COP 4610L: Java Networking Part 1 Page 11 Mark Llewellyn ©Transparency Properties of Distributed SystemsLocation Transparency – users do not necessarily need to know where exactly within the system a resource is located which they wish to utilize. Resources are


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UCF COP 4610L - Java Networking and the Internet

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