QoC-based Context Data Caching for Disaster Area Scenarios Mario Fanelli 1,2 , Luca Foschini 2 , Antonio Corradi 2 , Azzedine Boukerche 1 1 PARADISE Research Laboratory, SITE, University of Ottawa, Canada 2 Dipartimento di Elettronica, Informatica e Sistemistica (DEIS), University of Bologna, Italy {mario.fanelli, luca.foschini, antonio.corradi}@unibo.it, {mfanelli, boukerch}@site.uottawa.ca Abstract—Disaster area scenarios are the consequence of sudden and unexpected disasters due to either human or natural causes, such as terrorist attacks and earthquakes. Towards the main goal of saving as many human lives as possible, context-aware services are emerging as standard-de-facto solutions to improve the coordination of involved rescue teams. Unfortunately, the scarce resources (communication bandwidth, memory, etc.) lead to very tough deployment scenarios to deal with. This paper presents our real-world quality-based context data distribution infrastructure for context-aware services in disaster areas. The main contribution is a quality-based caching solution that self-adapts by using quality requirements associated to close neighbors. Collected simulation results confirm that our proposal improves both system scalability and data availability. Keywords-component: Disaster Areas; Context awareness; Quality of Context; QoC-based Context Data Caching. I. INTRODUCTION Recent advances in telecommunications and computer science have proposed novel scenarios in which mobile devices exchange messages without the need of pre-deployed wireless fixed infrastructures. By exploiting this possibility, a Mobile Ad-hoc NETwork (MANET) comprehends and puts together several mobile devices that communicate in a totally decentralized fashion by using only ad-hoc links [1]. MANETs well fit all those scenarios that do not assume wireless fixed infrastructures in charge of message routing. In particular, they are essential in disaster areas to substitute wireless fixed infrastructures in case of failures (for instance, the disaster could have damaged the infrastructures). Hence, novel approaches based, at the same time, on ad-hoc and infrastructure-based wireless communications can be suitably adopted in disaster areas to implement a scalable and reliable message routing mechanism. In such scenarios, context awareness intended as the provisioning of the current execution context (location, devices and people in the physical proximity, ...) to services can provide an accurate and timely characterization of the current situation [2]. We can envision several context-aware services: notable examples include context-aware disaster recovery services able to exploit context information on injured people and physical surroundings to guide rescue operations. While context awareness has been widely studied in the past [3], real-world context-aware services in disaster areas introduce some peculiar and still unresolved management issues. Above all, such systems have to i) memorize huge amounts of context data by means of distributed and unreliable data repositories; and ii) distribute them to all the interested mobile devices by using low-bandwidth wireless links. All above issues motivate the need for novel Context Data Distribution Infrastructures (CDDIs), namely infrastructures in charge of distributing context data to all the interested mobile entities, that transparently tackle all the low-level management issues. In addition, since context data could be safe-critical, additional research is required to develop efficient and reliable context data management for disaster areas. Towards CDDI management, the emerging notion of Quality of Context (QoC) deals with several and heterogeneous quality indicators, such as precision, freshness, etc. [4]. Given that rescue teams need context with different quality, the CDDI should introduce differentiated QoC-levels to memorize and distribute only the context data that will be actually used by destination nodes. Towards the realization of QoC-based CDDI, this paper proposes a novel quality-based caching algorithm that adopts differentiated quality levels to improve context data access. In particular, our proposal merges QoC requirements expressed by close neighbor nodes to enable local quality-based and self- adaptive caching: the core idea is to anticipate the removal of those data that will be no longer required (due to their poor quality) to cache more useful ones. The proposed solution, applied in a simulation case study, demonstrates to grant subscribed QoC and to reduce data dissemination traffic. II. QUALITY OF CONTEXT While QoC has received much attention in the past few years [4, 5], a widely adopted definition useful to understand what it represents is still missing. This section delves in QoC details to state better the needed terminology and research motivations. First, we introduce the related work. Second, we detail our motivating scenario and design guidelines. Finally, we present the main ideas of QoC-based context data caching. A. Related Work QoC has been widely studied in pervasive environments to face all the possible inaccuracies that a real-world system could introduce. In the first steps, different authors tried to elaborate about this concept. In [4], QoC contains “any information that describes the quality of information that is used as context information”. Instead, in [5], authors adopt a standard metrology ISO vocabulary, and present their own definition based on three principal attributes, namely precision, temporal 978-1-61284-231-8/11/$26.00 ©2011 IEEE This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE ICC 2011 proceedings