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State-of-the-art in Publish/Subscribe Middleware for Supporting Mobility

Sumant Tambe

EECS Preliminary ExaminationDecember 11, 2007

Vanderbilt University, Nashville, TN, USAContact : sutambe@dre.vanderbilt.edu

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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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Existing Middleware Technologies

Hardware

Domain-SpecificServicesCommon

Middleware ServicesDistribution

MiddlewareHost Infrastructure

MiddlewareOperating Systems

& Protocols

ApplicationsMiddleware Type Examples

Message Passing Message Passing using TCP/UDP

Remote Invocation Java RMI, CORBA

Asynchronous Notifications

CORBA AMI

Shared Spaces Linda, Java Spaces

Message Queuing IBM MQ-Series

Goal is to provide identity, time, and synchronization decouplingAbove mentioned middleware technologies do not provide all three

simultaneously.

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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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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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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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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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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 & 4Share subscriptions

Brokers 4 & 5don’t share subscriptions