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 :

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

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.

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

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

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

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

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