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1 State-of-the-art in Publish/Subscribe Middleware for Supporting Mobility Sumant Tambe EECS Preliminary Examination December 11, 2007 Vanderbilt University, Nashville, TN, USA Contact : sutambe@dre.vanderbilt.edusutambe@dre.vanderbilt.edu
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2 Information Dissemination Systems Examples of Information Dissemination Systems Online traffic information Stock price tracker News feeds Airline schedule display Pervasive computing Characteristics of Information Dissemination systems Information publishers Large number of information subscribers Inherently one-to-many Anonymous publishers and subscribers Asynchronous communication
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3 Existing Middleware Technologies Hardware Domain-Specific Services Common Middleware Services Distribution Middleware Host Infrastructure Middleware Operating Systems & Protocols Applications Middleware TypeExamples Message PassingMessage Passing using TCP/UDP Remote InvocationJava RMI, CORBA Asynchronous Notifications CORBA AMI Shared SpacesLinda, Java Spaces Message QueuingIBM MQ-Series Goal is to provide identity, time, and synchronization decoupling Above mentioned middleware technologies do not provide all three simultaneously.
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4 Publish/Subscribe Middleware Characteristics of Publish/subscribe middleware Inherently multicasting (one-to- many) Asynchronous communication Time decoupling Identity decoupling Synchronization decoupling Anonymous publishers Anonymous subscribers Implicit addressing Types of Publish/Subscribe Channel-based Topic-based (subject based) Content-based Content-based with patterns Context-based (local state) \Stocks\GroupA\MSFT Company“MSFT” Price>= $10 Volume>= 5000 My Account Balance>= $10,000
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5 Challenges in Information Dissemination Systems Supporting Mobility Physical mobility of application components While online/offline Potentially large number of publishers and subscribers Frequent connections and disconnections To conserve power, bandwidth Changes in underlying network topology Ad-hoc networks, (e.g., disaster recovery) Support location-based services Approximate location/range Limited time validity (e.g., roads to downtown closed till 3 a.m.) YOU ARE SOMEWHERE HERE
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6 Solution Domain Challenges in Supporting Mobility (1/2) Location transparency Many applications are location independent (e.g., stock tracker) Completeness of events Events should not be lost due to mobility or connection/disconnections Retransmission should be avoided Ordering of events Events should be delivered in the order of the sender No duplicate delivery Due to rapid mobility Responsiveness No QoS degradation No indirection (e.g., Mobile IP) Publisher Subscriber
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7 Solution Domain Challenges in Supporting Mobility (2/2) Location-awareness E.g., Parking place notifications “Location” is the local context (variable) Continuous change in location Propagation of location dependent subscriptions Minimization of propagation delay Approximate matching of events Approximate subscriptions Approximate events Existing Publish/Subscribe middleware although useful, but is not adequate S: (close to downtown Toronto) AND (about 75 square meters in size) AND (no more than $1000) AND (close to major grocery shopping) E: (location, close to downtown) (size, big) (price, expensive) (shopping, close-by) e3 should have been received
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8 Publish/Subscribe Middleware Solutions (1/2) Creating overlay network of event brokers in dynamic environment Dynamic dispatching tree in JEDI Selecting subscriber group leader Adapt to changing topology SHOPPARENT algorithm Considers locality of subscribers Greedy, local optimizations only Heuristic-based overhead calculation Location transparency Subscription handoff protocol in REBECA Completeness guarantee Source FIFO order No duplicates Brokers 3 & 4 Share subscriptions Brokers 4 & 5 don’t share subscriptions
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