Vol.1 No.3 September, 2005
Mobile Multimedia Computing and Communications

Editorial (pp179-179)
        C.-Y. Chang and J.-H. Ma  

Research articles:
Design of a Hierarchical Group to Realize a Scalable Group (pp180-197)
        Y. Nishimura, N. Hayashibara, T. Enokido, and M. Takizawa
According to the advance of computer and network technologies, information systems are getting scalable. Especially, peer-to-peer (P2P) overlay networks and Grid computing system are now taking a central position in information systems. In these systems, a large number of peer processes are cooperating. In group communication, each peer process sends a message to multiple processes while receiving messages from multiple processes. Here, messages transmitted are required to be causally/totally delivered to every common destination of the messages. The computation and communication complexity is $O(n)$ to $O(n^2)$ for the number $n$ of peer processes. In order to reduce the overheads, a group is divided into smaller subgroups where processes exchange messages with other subgroups only through gateway processes while processes directly exchange messages in each subgroup. In this paper, we discuss a hierarchical group protocol aiming at reducing communication and computation overheads for supporting a scalable group of cooperating peer processes. In traditional hierarchical group protocols, each subgroup communicates with another subgroup through a single gateway communication link. A gateway communication link among subgroups implies performance bottleneck and a single point of failure. In order to increase the throughput and reliability of inter-subgroup communication, messages are in parallel transmitted in a network striping way through multiple channels between multiple processes in the subgroups. We discuss a striping multi-channel inter-subgroup communication protocol (SMIP). We evaluate SMIP in terms of stability of bandwidth and message loss ratio and show how SMIP can support more stable bandwidth and message loss ratio.

A New VOD Technique to Support Client Mobility (pp198-210)
        K. Sato, M. Katsumoto, and T. Miki
This paper introduces fragmented patching, a new video on-demand technique that enables mobile clients to receive a video stream while moving freely. Patching techniques that significantly reduce the required network bandwidth through multicasting have shown potential for on-demand video distribution. However, patch-flow techniques based on unicast data are unsuitable for providing services to mobile clients because an intricate form of mobile routing is needed for each unicast flow to enable it to individually follow a moving client. Conversely, in fragmented patching, patch flows are sent via broadcasting. The patch flows are divided into segments to avoid increasing traffic due to broadcasting; each of the segments is aggregated to be shared with as many clients as possible. In addition, we have considered broadcasting shared flows also to eliminate any overhead arising from multicast tree construction. This paper analyzes the network bandwidth required for fragmented patching for two cases: when the patch flow is broadcast and the shared flow is multicast, and when both the patch and shared flows are broadcast. Numerical analysis based on the traffic intensity (Erlang) has revealed that the aggregation effect caused by segmenting patch flows counteracts the increase in traffic caused by broadcasting. It also showed that fragmented patching reduces the required bandwidth by a greater extent than other patching techniques even when both the patch and shared flows are broadcast.

Round-Robin with FCFS Preemption: A Simple MAC Scheduling Scheme for Bluetooth Piconet  (pp211-223)
        L.-H. Yen and C.-H. Liao
Bluetooth is a short-range TDD (Time Division Duplex) wireless network that supports both circuit- and packet-oriented applications. A piconet is composed of a device configured as master and at most seven other devices acting as slaves. At Medium Access Control (MAC) layer, the master can select a slave to send a data packet and until then, the slave is not allowed to transmit. Round-Robin (RR) and Exhaustive Round-Robin (ERR) are two elementary MAC scheduling schemes that are both simple and efficient. This paper proposes RR-FCFS, a simple MAC scheduling scheme that has the same advantages as RR and ERR. RR-FCFS acts as RR if the master's queue is empty and starts transmitting packets in first-come-first-serve order otherwise. The simulation results show that RR-FCFS's performance in terms of packet delay and queue length is comparable with those of RR and ERR.

Scalable Inter-Vehicle Communication Protocol (pp224-234)
        M. Durresi, A. Durresi, and L. Barolli
In this paper we present a sensor inter-vehicle communication protocol based on geographical routing. Sensors installed in cars continuously gather important information about: air bags, distance detection, mechanical and electronic parts, tire pressure, collision force, direction of impact and the car and its passengers' conditions. Our proposed protocol enables transmission of these information on point-to-point communications between cars in highway. The protocol is designed for highway travelers but can be used in any mobile ad-hoc network. The highway is divided in virtual cells, which moves as the vehicles moves. The cell members choose a center that will behave for a certain time interval as a Base Station. Every node has its geographical position given by Global Positioning System (GPS). When a source node has a message for a destination node, forwards it to its Cell Center. Then the message is forwarded through the other Cell Centers. The Cell Centers first verifies if the destination node belongs to their cell. Finally the destination Cell Center will send the message to the destination node. Our simulation results show that our proposed protocol improves the network utilization compared to existing inter-vehicles protocols. The protocol can be used to implement differentiated mobile services and message prioritization. Through simulation evaluations, we show that our protocol is very scalable and reduces the latency compared existing solutions.

Hierarchical Semantic-Based Index for Ad Hoc Image Retrieval (pp235-254)
        B. Yang and A. R. Hurson  
Ad hoc networks have received considerable research attention by provisions of wireless communications without location limitations and pre-built fixed infrastructure. Because of the absence of any static support infrastructure, ad hoc networks are prone to several limitations such as bandwidth, connectivity, and power. The traditional content-based image retrieval approaches employed in ad hoc networks may result in either high search cost or low fault tolerance. In this paper, we propose and analyze a decentralized non-flooding image retrieval scheme in multi-hop mobile ad hoc networks ─ Semantic Ad hoc Image Retrieval (SAIR). The novelty of SAIR stems from several factors including: (1) representation of image contents using first-order logic expressions; (2) clustering mobile nodes based on their data contents; (3) organizing image data with a hierarchical semantic-based indexing infrastructure; (4) performing content-based image retrieval within a reduced scope of mobile nodes. Through extensive simulations, we show that relative to the flooding strategy, SAIR can retrieve the semantically most similar image objects by accessing only a small portion of the mobile nodes with much lower search cost. Moreover, it is scalable to large network sizes and large number of data objects.

PATH: A Software Framework for Interactive Visualization of Behavior History (pp255-269)
        M. Ito, J. Nakazawa, and H. Tokuda
This paper presents an interactive analysis and visualization framework for behavior histories, called mPATH framework. In ubiquitous computing environment, it is possible to infer human activities through various sensors and accumulation of their data. Visualization of such human activities is one of the key issues in terms of memory and sharing our experiences, since it acts as a memory assist when we recall, talk about, and report what we did in the past. However, current approaches for analysis and visualization are designed for a specific use, and therefore can not be applied to diverse use. Our approach provides users with programmability by a visual language interface for analyzing and visualizing the behavior histories. The framework includes icons representing data sources of behavior histories, analysis filters, and viewers. By composing them, users can create their own analysis method of behavior histories. We also demonstrate several visualizations on the framework. The visualizations show the flexibility of creating behavior history viewers on the mPATH framework.

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