Research Articles

Analysis of Connectivity and Session Management for Mobile Peer-to-Peer Applications (081-112)  
        Otso Kassinen, Timo Koskela, Erkki Harjula, Jukka Riekki, and Mika Ylianttila 
Mobile applications utilizing wireless networks are growing in popularity as increasingly capable terminals and advanced networking technologies emerge. In order to provide a seamless user experience, applications must be able to rely on an intelligent mobile middleware that hides the complexity of underlying technologies and allows developers to solve application-specific problems instead. A middleware should take care of generic networking functionality such as management of user communities, signalling for sessions, interaction with content-licensing services, and management of the terminal’s networking resources. This paper focuses on two major components of a prototype peer-to-peer networking middleware: a solution for connectivity management and another for session management. First, the connectivity management solution is discussed. The solution formalizes cross-layer resource optimization and employs upgradeable state machines to make connectivity selections based on context data and user preference, aiming to always provide the best connection for different communications and keep the system extensible. Second, the session management solution is discussed. The solution enables installation of missing software dynamically on a terminal when another user proposes a mutual application session. This greatly increases users’ possibilities to initiate sessions with each other. In this paper, design principles behind each of the novel solutions are studied, their prototype implementations are evaluated on the Symbian smartphone platform, and they are contrasted with existing technologies. A lightweight Session Initiation Protocol (SIP) stack has also been implemented as a component for the middleware. Future work concerning the connectivity and session management solutions includes evaluation of the technologies in more realistic settings than was possible within the work for this paper.

Fault Tolerance in the Mobile Environment (113-124)  
        Daniel C. Doolan, Sabin Tabirca, and Laurence T. Yang 
In general it is assumed that a parallel program will execute on reliable hardware. A fault tolerant program and underlying infrastructure should be capable of surviving failures such as system crashes and network failures. At the highest level the application should be capable of automatically recovering from a set of faults without any change to the apparent behaviour of the program. The process of checkpointing may be used to allow a program to save its state to persistent storage, abort and restart from the checkpoint. Several fault tolerant MPI implementations are currently in existence, for example MPICH-V is considered to be one of the most complete, featuring checkpointing and message logs to allow aborted processes to be replaced. No matter how sophisticated a fault tolerant system may be, it can never be completely relied upon, as there is always the possibility of a complete system failure. It is one thing to develop fault tolerant applications on high end dedicated clusters and supercomputers, however applying fault tolerance to the realm of mobile parallel computing presents an entire new series of challenges that are inexorably linked with the unpredictable nature of wireless communication systems. Two differing strategies for fault tolerance in the mobile Bluetooth wireless environment will be presented and compared to see which should be adopted over another.

A New Lossy and Lossless Image Representation by using Non-symmetry and Anti-packing Model with Rectangles for Gray Images (125-139)  
        Mudar Sarem, Yun-Ping Zheng, and Chuan-Bo Chen 
With the rapid development of mobile communication systems, demands for the transmission of multimedia information are increasing day by day. The effective transmission of images can be increased by getting smaller image file that is obtained by compression. However, image quality is often sacrificed in the compression process. Therefore, there is a need to represent images with less data storage without sacrificing the image quality. In this paper, inspired by the concept of the packing problem, we present a new Non-symmetry and Anti-packing Model with Rectangles (NAMR) for lossy and lossless image representation in order to represent the pattern more effectively and flexiblely. Also, in this paper, we propose an algorithm of NAMR and analyze the data amount of this algorithm. The theoretical analyses and experimental results presented in this paper show that when the representation method of NAMR is compared with that of the popular linear quadtree, not only can the former reduce the data storage much more effectively than the latter in lossless case, but also the former has a better reconstruction quality than the latter in lossy case.

An Event-Driven Wearable System for Supporting Pit-crew and Audiences on Motorbike Races (140-157)  
        Tsutomu Terada, Masakazu Miyamae, Yasue Kishino, Takahito Fukuda, and Masahiko Tsukamoto 
Motorbike racing is one of the most popular motorsports and many fans visit circuits to watch races. However, since audiences and pit crews can only obtain limited information, it is difficult for them to get detailed information about teams except for high ranking teams and few popular teams. To solve this problem, we propose an information browsing system for pit crews and audiences who use wearable computers. This system allows pit crew to browse for various race information easily and effortlessly, and it can entertain audiences much more.

Distributed Information Management and Publish/Subscribe in VANETs (158-180)
        Vivian Prinz, Michele Brocco, and Wolfgang. Woerndl
Wireless communication is particularly powerful in vehicular ad hoc networks (VANETs) as it implies important possibilities to enhance traffic safety. For this purpose, a car-to-car (C2C) communication system should provide distributed information management. For example, it should guarantee the availability of a black ice warning for the duration of its validity. In addition, the Publish/Subscribe (Pub/Sub) paradigm allows for information filtering and tracking of changes in the information environment. Thus, vehicles could monitor traffic changes, for example.}{This article introduces the application of structured peer-to-peer (P2P) algorithms and P2P/Distributed Hash Table (DHT)-based Pub/Sub for the named functionalities. To allow for their application given high mobilities and to provide location-awareness, the vehicular network is segmented into separate, interacting P2P networks. Cars manage information of their own segment and exchange them between adjacent segments if necessary. The Pub/Sub functionality is built on top of the P2P segments' DHTs. This way, Pub/Sub can be applied as there is no need to maintain a vehicular broker tree. The proposed solution enables C2C applications to publish information referring to certain areas or validity durations. In addition, they can request, modify and delete this information and solely interested vehicles can be notified about these events.

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