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Outline Announcement Existing distributed systems Final Review 01 17 19 COP5611 1 Announcement The final exam will be 5 30 7 30 pm on April 29 2003 in LOV 103 The exam will be open book and open note You can have at most three hours if necessary 01 17 19 COP5611 2 Existing Distributed Systems There are commercial as well as experimental distributed systems available In general theses systems are not generic distributed systems as defined in this class Rather they are designed to offer some good specific services with the hope to generate profits from those services These are mainly based on the chapters from the book by A S Tanenbaum and M van Steen 01 17 19 COP5611 3 Distributed Object based Systems Distributed object based systems In these systems everything is treated as an object and clients are offered services and resources in the form of objects they can invoke Examples CORBA Microsoft s DCOM Globe Global Object Based Environment 01 17 19 COP5611 4 CORBA 01 17 19 COP5611 5 Distributed Component Object Model 01 17 19 COP5611 6 Distributed Component Object Model cont 01 17 19 COP5611 7 GLOBE 01 17 19 COP5611 8 Object Model The general organization of a CORBA system 01 17 19 COP5611 9 Distributed Document based Systems A simple paradigm Everything is a document A distributed document based system allows a user to exchange information Examples World wide web Can be viewed as a huge distributed system consisting of millions of clients and servers Lotus notes Primarily based on databases 01 17 19 COP5611 10 World Wide Web WWW is essentially a huge client server system with millions of servers distributed worldwide Each server maintains a collection of documents Each document is stored as a file Or can be generated on request ASP JSP PHP The simplest way to refer to a document is by means of a reference called Uniform Resource Locator A client interacts with servers with browsers 01 17 19 COP5611 11 The World Wide Web Overall organization of the Web 01 17 19 COP5611 12 Architectural Overview The principle of using server side CGI programs 01 17 19 COP5611 13 Architectural Overview cont Architectural details of a client and server in the Web 01 17 19 COP5611 14 Web Proxy Caching The principle of cooperative caching 01 17 19 COP5611 15 Server Replication The principle working of the Akami CDN 01 17 19 COP5611 16 Security 01 17 19 COP5611 17 Lotus Notes The general organization of a Lotus Notes system 01 17 19 COP5611 18 Processes in Lotus Notes 01 17 19 COP5611 19 Processes in Lotus Notes cont Request handling in a cluster of Domino servers 01 17 19 COP5611 20 Distributed Coordination based Systems Newer generation of distributed systems Various components of a system are inherently distributed One of the major issues is coordination of activities 01 17 19 COP5611 21 TIB Rendezvous 01 17 19 COP5611 22 TIB Rendezvous cont 01 17 19 COP5611 23 Overview of Jini 01 17 19 COP5611 24 Jini Architecture 01 17 19 COP5611 25 Communication Events in Jini 01 17 19 COP5611 26 Announcement Final exam will be on April 29 2003 From 5 30 7 30 PM 8 30 PM at most you can have At Love 103 It is an open book open note exam Please plan to come around 5 20 pm so that we can start as early as possible 01 17 19 COP5611 27 Important Topics These are the main focus for the purpose of the final exam However other topics are not excluded entirely Important ones Logical clocks vector clocks Causal ordering of messages Consistent global state checkpoint Lamport s algorithm for mutual exclusion Lab 1 also included Lab 2 Distributed scheduling algorithms issues Synchronous checkpointing and recovery asynchronous checkpointing and recovery Commit protocols non blocking commit protocols Static voting protocols Access matrix model Implementation issues 01 17 19 COP5611 28 Distributed Systems A distributed system is a collection of independent computers that appears to its users as a single coherent system Independent computers mean that they do not share memory or clock The computers communicate with each other by exchanging messages over a communication network Distributed operating systems are much like the traditional operating systems Resource management User friendliness The key concept is transparency 01 17 19 COP5611 29 Clients and Servers General interaction between a client and a server 01 17 19 COP5611 30 Layered Protocols Layers interfaces and protocols in the OSI model 01 17 19 COP5611 31 Network Layer The primary task of a network layer is routing The most widely used network protocol is the connection less IP Internet Protocol Each IP packet is routed to its destination independent of all others A connection oriented protocol is gaining popularity Virtual channel in ATM networks 01 17 19 COP5611 32 Transport Layer This layer is the last part of a basic network protocol stack In other words this layer can be used by application developers An important aspect of this layer is to provide end toend communication The Internet transport protocol is called TCP Transmission Control Protocol The Internet protocol also supports a connectionless transport protocol called UDP Universal Datagram Protocol 01 17 19 COP5611 33 Sockets cont Connection oriented communication pattern using sockets 01 17 19 COP5611 34 A Multithreaded Server 01 17 19 COP5611 35 The Message Passing Model The message passing model provides two basic communication primitives Send and receive Send has two logical parameters a message and its destination Receive has two logical parameters the source and a buffer for storing the message 01 17 19 COP5611 36 Semantics of Send and Receive Primitives There are several design issues regarding send and receive primitives Buffered or un buffered Blocking vs non blocking primitives With blocking primitives the send does not return control until the message has been sent or received and the receive does not return control until a message is copied to the buffer With non blocking primitives the send returns control as the message is copied and the receive signals its intention to receive a message and provide a buffer for it 01 17 19 COP5611 37 Semantics of Send and Receive Primitives cont Synchronous vs asynchronous primitives With synchronous primitives a SEND primitive is blocked until a corresponding RECEIVE primitive is executed With asynchronous primitives a SEND primitive does not block if there is no corresponding execution of a RECEIVE primitive The messages are buffered 01 17 19 COP5611 38
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