Adaptive Directory Services for Highly Dynamic Environments Fabio Kon Department of Computer Science University of São Paulo, Brazil Dilma M. Silva IBM T. J. Watson Research Center

Middleware’2001 WIP 2 Directory Services l Locate objects based on their name and/or attributes l Analogous to phone directories l White pages ~ CORBA Name Service l Yellow pages ~ CORBA Trader l Popular Directory Services: l LDAP / X.500 l CORBA Trading Object Service l Jini Lookup Service

Middleware’2001 WIP 3 Problems in Mobile and Highly Dynamic Environments l Directory services help clients locate server objects l But in dynamic environments l Servers are dynamically added and removed l Servers crash or become unreachable l Servers may migrate from one node to the other l Clients may move while they are looking for appropriate servers

Middleware’2001 WIP 4 Motivation and Objective l Existing Directory Services are not prepared to deal with such dynamic environments. l With mobile and ubiquitous computing, dynamic environments will become more and more common. l Objective: investigate what facilities must be added to existing systems to support such dynamism.

Middleware’2001 WIP 5 Target Application The Sidam Project Prototype Road Traffic Information System Motivation: São Paulo is a city of 17M people. Road traffic is a complete chaos. Billions/year are lost in traffic jams. Goal: Develop a prototype of a very-large-scale system to provide relevant information about traffic conditions in real-time to mobile users.

Middleware’2001 WIP 6 Traffic Information System l Highly replicated (millions of users) l No Centralized Service l Strict consistency not possible l Some consistency is required: data that is too old is useless l Extremely distributed Production of data Consumption of data

Middleware’2001 WIP 7 The Java Prototype l Information Servers l Hold traffic information for a few neighbourhoods l Location Servers l Used by clients to locate Information Servers based on the region of the city in which the client is interested l A Directory Service of Information Servers

Middleware’2001 WIP 8 Support for Dynamic Reconfiguration and Adaptation Consistency objects are responsible for implementing different consistency policies l When Information Servers are killed, the system reconfigures itself dynamically to update the directory service

Middleware’2001 WIP 9 Ongoing Work l Trigger automatic reconfiguration when any component in the system fails. l Creation and destruction of Information and Location Servers according to system load. l Migration of components according to load and physical location of clients. l Goal: increase availability and response time of the system.

Middleware’2001 WIP 10 For more information Fabio Kon: SIDAM Web site: Distributed Systems Group Web site: