Hybrid Dissemination Based Scalable and Adaptive Context Delivery for Ubiquitous Computing Lenin Mehedy, Md. Kamrul Hasan, Young Koo Lee 1 , Sungyoung Lee, Sang Man Han Real Time & Multimedia Lab, Department of Computer Engineering, Kyung Hee University, 449-701, Republic of Korea {lenin, kamrul, sylee, i30000}@oslab.khu.ac.kr, 1 yklee@khu.ac.kr Abstract. Context delivery is an inevitable issue for ubiquitous computing. Context-aware middlewares perform all the functions of context sensing, infer- ring and delivery to context-aware applications. But one of the major issues for these middlewares is to devise a context delivery scheme that is scalable as well as efficient. Pure unicast or pure broadcast based dissemination can not provide scalability as well as less average latency. In this paper we present a scalable context delivery mechanism for context-aware middlewares based on hybrid data dissemination technique where the most requested data are broad- casted and the rest are delivered through unicast. Our scheme is adaptive in the sense that it dynamically differentiates hot (most requested) and cold (less re- quested) data according to request rate and waiting time. Inclusion of lease mechanism and bandwidth division further allows us to reduce network traffic and average latency. We validated our claim through extensive simulation. 1 Introduction Context awareness is the ability to sense, interpret and respond to the situation of an entity (e.g. user, application) [2]. Often, the term "Context-aware Computing" is used synonymously to Mark Weiser’s revolutionary concept of Ubiquitous Computing [1] as every future application will have context-awareness. Context-aware middleware performs all the functions of context sensing, inferring and then delivers to smart applications (see [4] for a survey). Thus every context-aware middlewares usually have the following three main phases of execution: a) Acquisition of raw sensor data, b) Context inference from the sensory data, c) Context delivery to applications. This paper focuses on the context delivery mechanism for such middlewares. Our work is motivated by the unavoidable need of scalable context delivery in large smart environments (such as a corporate office, academic building, shopping complex etc.) where numerous context-aware applications (we interchangeably use client or receivers), running on mobile devices like PDA or stationary devices (desk- 1 Dr. Young Koo Lee is the corresponding author