A scalable framework for mobile real-time group communication services

A scalable framework for mobile real-time group communication services is developed in this paper. Examples for possible applications of this framework are mobile social networks, mobile conference calls, mobile instant messaging services, and mobile multi-player on-line games. A key requirement for enabling a real-time group communication service is the tight constraint imposed on the call delivery delay. Since establishing such communication service for a group of independent mobile users under a tight delay constraint is NP-hard, a two-tier architecture is proposed, that can meet the delay constraint imposed by the real-time service requirement for many independent mobile clients in a scalable manner. This goal is achieved by two dimensional partition of the space, first by organization and then geographically. Both the time and memory complexity associated with the location management of N mobile users are O(N) for the location management provided by the proposed framework, while a distributed scheme requires O(N²) for both time and memory complexity.     

GCS-MA: A group communication system for mobile agents

Reliable messaging is a key component necessary for mobile agent systems. Current researches focus on reliable one-to-one message delivery to mobile agents. But how to implement a group communication system for mobile agents remains an open issue, which is a powerful block that facilitates the development of fault-tolerant mobile agent systems. In this paper, we propose a group communication system for mobile agents (GCS-MA), which includes totally ordered multicast and membership management functions. We divide a group of mobile agents into several agent clusters, and each agent cluster consists of all mobile agents residing in the same sub-network and is managed by a special module, named coordinator. Then, all coordinators form a ring-based overlay for interchanging messages between clusters. We present a token-based algorithm, an intra-cluster messaging algorithm and an inter-cluster migration algorithm to achieve atomicity and total ordering properties of multicast messages, by building a membership protocol on top of the clustering and failure detection mechanisms. Performance issues of the proposed system have been analysed through simulations. We also describe the application of the proposed system in the context of the service cooperation middleware (SCM) project.     

A self-verification authentication mechanism for mobile satellite communication systems

In order to provide an opportunity to make personal communication as broad as possible, mobile satellite communication systems have recently drawn much attention. However, any communication system raises two major challenging issues: (1) how to determine whether actors are whom they claim to be; and (2) how to protect data against unauthorized disclosure. Although the secret-key cryptosystem (SKC) and the public-key cryptosystem (PKC) have been developed to provide well-defined security services to address these issues each has serous drawbacks while SKC-based authentication schemes have the common demerit that the server which maintains the secret-key table becomes an attractive target for numerous intrusions, PKC-based schemes suffer from the expensive complexity of the public-key infrastructure (PKI) and a high computation overhead. Therefore, in this paper, a self-verification authentication mechanism with lower computation and key management cost is introduced.     

Architecture for mobile group communication in campus environment

The demand for group communication using smart devices in campus environment is increasing rapidly. In this paper, we design an architecture for a mobile group communication system (MGCS) on campus by using Wi-Fi networks and smart devices. The architecture is composed of a web-based system and a smart device based mobile system. Through the systems, users on campus create community/mobile group, maintain dynamic group membership, and reliably deliver the message to other users. We use the common features of many smart devices to develop a prototype that works on off-the-shelf hardware. In the experimental section, we demonstrate our system using various real scenarios which can occur in university campuses.     

Adaptive group scheduling mechanism using mobile agents in peer-to-peer grid computing environment

Peer-to-peer grid computing is an attractive computing paradigm for high throughput applications. However, both volatility due to the autonomy of volunteers (i.e., resource providers) and the heterogeneous properties of volunteers are challenging problems in the scheduling procedure. Therefore, it is necessary to develop a scheduling mechanism that adapts to a dynamic peer-to-peer grid computing environment. In this paper, we propose a Mobile Agent based Adaptive Group Scheduling Mechanism (MAAGSM). The MAAGSM classifies and constructs volunteer groups to perform a scheduling mechanism according to the properties of volunteers such as volunteer autonomy failures, volunteer availability, and volunteering service time. In addition, the MAAGSM exploits a mobile agent technology to adaptively conduct various scheduling, fault tolerance, and replication algorithms suitable for each volunteer group. Furthermore, we demonstrate that the MAAGSM improves performance by evaluating the scheduling mechanism in Korea@Home. SungJin Choi is a Ph.D. student in the Department of Computer Science and Engineering at Korea University. His research interests include mobile agent, peer-to-peer computing, grid computing, and distributed systems. Mr. Choi received a M.S. in computer science from Korea University. He is a student member of the IEEE. MaengSoon Baik is a senior research member at the SAMSUNG SDS Research & Develop Center. His research interests include mobile agent, grid computing, server virtualization, storage virtualization, and utility computing. Dr. Baik received a Ph.D. in computer science from Korea University. JoonMin Gil is a professor in the Department of Computer Science Education at Catholic University of Daegu, Korea. His recent research interests include grid computing, distributed and parallel computing, Internet computing, P2P networks, and wireless networks. Dr. Gil received his Ph.D. in computer science from Korea University. He is a member of the IEEE and the IEICE. SoonYoung Jung is a professor in the Department of Computer Science Education at Korea University. His research interests include grid computing, web-based education systems, database systems, knowledge management systems, and mobile computing. Dr. Jung received his Ph.D. in computer science from Korea University. ChongSun Hwang is a professor in the Department of Computer Science and Engineering at Korea University. His research interests include distributed systems, distributed algorithms, and mobile computing. Dr. Hwang received a Ph.D. in statistics and computer science from the University of Georgia.     

A pricing mechanism for scalable video delivery

Many video applications tolerate continuous media (CM) scaling. Scaling is acceptable due to human tolerance to degradation in picture quality, frame loss, and end-to-end delay. CM scaling enables the network to utilize its resources efficiently for supporting additional customers and to increase its revenue. However, due to quality degradation, users will not be willing to tolerate scaling unless it is coupled with monetary or availability incentives. We propose a pricing policy and a corresponding admission control scheme for scalable video applications. The pricing policy is two-tiered, based on a connection set-up component and a scalable component. Connections that are more scalable are charged less, but are more liable to be degraded. The proposed policy trades off performance degradation with monetary incentives to improve user benefit and network revenue and to decrease the blocking probability of connection requests. We demonstrate by means of simulation that this policy encourages users to specify the scalability of an application to the network.     

A scalable low-latency cache invalidation strategy for mobile environments

Caching frequently accessed data items on the client side is an effective technique for improving performance in a mobile environment. Classical cache invalidation strategies are not suitable for mobile environments due to frequent disconnections and mobility of the clients. One attractive cache invalidation technique is based on invalidation reports (IRs). However, the IR-based cache invalidation solution has two major drawbacks, which have not been addressed in previous research. First, there is a long query latency associated with this solution since a client cannot answer the query until the next IR interval. Second, when the server updates a hot data item, all clients have to query the server and get the data from the server separately, which wastes a large amount of bandwidth. In this paper, we propose an IR-based cache invalidation algorithm, which can significantly reduce the query latency and efficiently utilize the broadcast bandwidth. Detailed analytical analysis and simulation experiments are carried out to evaluate the proposed methodology. Compared to previous IR-based schemes, our scheme can significantly improve the throughput and reduce the query latency, the number of uplink request, and the broadcast bandwidth requirements.     

A scalable encryption scheme for multi-privileged group communications

In multi-privileged group communications, since users, who can subscribe to different data streams according to their interests, have multiple access privileges, security issues are more difficult to be solved than those in traditional group communications. The common drawback of traditional key management schemes is that they will result in the “one-affect-many” problem, because they use a key graph to manage all the keys in a group, which makes one key being shared by many users. Recently, a key-policy attribute-based encryption (KP-ABE) scheme is proposed to encrypt messages to multiple users efficiently, which has been applied in secure multi-privileged group communications. However, user revocation in KP-ABE is still not resolved when applied to multi-privileged group communications. So, in this paper, by uniquely combining a collusion-resistant broadcast encryption system and a KP-ABE system with a non-monotone access structure, we propose a scalable encryption scheme for multi-privileged group communications (EMGC). Based on the features of different multi-privileged group communication systems, we also propose two constructions for our EMGC scheme. With the two constructions, a system can support a user not only to join/leave a group at will, but also to change his access privilege on demand, and the expenses during rekeying operations are small. Therefore, our scheme, which can accommodate a dynamic group of users, is more applicable to multi-privileged group communications.     

Local communication of multiple mobile robots: design of group behavior for efficient communication

A novel design method of robot behavior is discussed to realize efficient local communication for cooperation of multiple mobile robots. Local communication is now increasingly utilized in cooperative many-robot systems because of its advantages of load distribution and simple implementation. In its usage, the design of each robot's behavior is a very important issue since it has a significant effect upon the communication efficiency in a collective manner. In this study, we introduce a simple group behavior and analyze how it improves the performance of local communication among many mobile robots. The performance is evaluated using the information transmission time that plays a crucial part in effective cooperation. Next, the optimal group size is analytically derived by minimizing the transmission time. The effectiveness of the analytical design method is verified by computer simulations of many-robot communication.     

A scalable architecture for 3D map navigation on mobile devices

Mobile devices such as smart phones or tablets are rapidly increasing their graphics and networking capabilities. However, real-time visualization of 3D maps is still a challenging task to accomplish on such limited devices. In this paper, we describe the principles involved in the design and development of a scalable client–server architecture for delivering 3D maps over wireless networks to mobile devices. We have developed a hybrid adaptive streaming and rendering method that distributes the 3D map rendering task between the mobile clients and a remote server. This architecture provides support for efficient delivery of 3D contents to mobile clients according to their capabilities. As a proof of concept, we have implemented a prototype and carried out exhaustive experiments considering different scenarios and hundreds of concurrent connected clients. The analysis of the server workload and the mobile clients performance show that our architecture achieves a great scalability and performance even when using low-end hardware.     

无线移动环境下双链路通信机制的研究与应用

针对现有切换机制和算法存在切换延迟较大、丢包率较高、不够稳定可靠等问题,提出一种双链路通信机制,给出一种双链路选择和数据传输算法,通过平滑处理获取精确信号质量,根据差值阈值控制两条通信链路在适当时机进行切换,并使用双线程进行数据转发。实验结果表明,与单链路机制相比,双链路机制不会出现延迟脉冲,丢包率接近于零,平均吞吐量提升了20%,可以应用到轨道交通、高速公路等具有高速移动子网的应用场合。     

A survey of theories for mobile agents

This paper presents a comparative survey of formalisms related to mobile agents. It describes the -calculus and its extensions, the Ambient calculus, Petri nets, Actors, and the family of generative communication languages. Each of these formalisms defines a mathematical framework that can be used to reason about mobile code; they vary greatly in their expressiveness, in the mechanisms they provide to specify mobile code based applications and in their practical usefulness for the validation and the verification of such applications. In this paper we show how these formalisms can be used to represent the mobility and communication aspects of two mobile code environments: Obliq and Messengers. We compare and classify the different formalisms with respect to mobility and discuss some shortcomings and desirable extensions. We also point to other emerging concepts in formalisms for mobile code systems.     

A scalable network forensics mechanism for stealthy self-propagating attacks

Network forensics supports capabilities such as attacker identification and attack reconstruction, which complement the traditional intrusion detection and perimeter defense techniques in building a robust security mechanism. Attacker identification pinpoints attack origin to deter future attackers, while attack reconstruction reveals attack causality and network vulnerabilities. In this paper, we discuss the problem and feasibility of back tracking the origin of a self-propagating stealth attack when given a network traffic trace for a sufficiently long period of time. We propose a network forensics mechanism that is scalable in computation time and space while maintaining high accuracy in the identification of the attack origin. We further develop a data reduction method to filter out attack-irrelevant data and only retain evidence relevant to potential attacks for a post-mortem investigation. Using real-world trace driven experiments, we evaluate the performance of the proposed mechanism and show that we can trim down up to 97% of attack-irrelevant network traffic and successfully identify attack origin.     

A secure migration process for mobile agents

This article describes a decentralized secure migration process of mobile agents between Mobile‐C agencies. Mobile‐C is an IEEE Foundation for Intelligent Physical Agents (FIPA) standard compliant multi‐agent platform for supporting C/C++ mobile and stationary agents. Mobile‐C is specially designed for mechatronic and factory automation systems where malicious agents may cause physical damage to machinery and personnel. As a mobile agent migrates from one agency to another in an open network, the security concern of mobile agent systems should not be neglected. Security breaches can be minimized considerably if an agency only accepts mobile agents from agencies known and trusted by the system administrator. In Mobile‐C, a strong authentication process is used by sender and receiver agencies to authenticate each other before agent migration. The security framework also aims to guarantee the integrity and confidentiality of the mobile agent while it is in transit. This assures that all agents within an agency framework were introduced to that framework under the supervision and permission of a trusted administrator. The Mobile‐C Security protocol is inspired from the Secure Shell (SSH) protocol, which avoids a single point of failure since it does not rely on a singular remote third party for the security process. In this protocol, both agencies must authenticate each other using public key authentication, before a secure migration process. After successful authentication, an encrypted mobile agent is transferred and its integrity is verified by the receiver agency. This article describes the Mobile‐C secure migration process and presents a comparison study with the SSH protocol. The performance analysis of the secure migration process is performed by comparing the turnaround time of mobile agent with and without security options in a homogeneous environment. Copyright © 2010 John Wiley & Sons, Ltd.     

CuNoC: A dynamic scalable communication structure for dynamically reconfigurable FPGAs

The growing complexity of integrated circuits imposes to the designers to change and direct the traditional bus-based design concepts towards NoC-based. Networks on-chip (NoCs) are emerging as a viable solution to the existing interconnection architectures which are especially characterized by high level of parallelism, high performances and scalability. The already proposed NoC architectures in the literature are destined to System-on-chip (SoCs) designs. For a FPGA-based system, in order to take all benefits from this technology, the proposed NoCs are not suitable. In this paper, we present a new paradigm called CuNoC for intercommunication between modules dynamically placed on a chip for the FPGA-based reconfigurable devices. The CuNoC is based on a scalable communication unit characterized by unique architecture, arbitration policy base on the priority-to-the-right rule and modified XY adaptive routing algorithm. The CuNoC is namely adapted and suited to the FPGA-based reconfigurable devices but it can be also adapted with small modifications to all other systems which need an efficient communication medium. We present the basic concept of this communication approach, its main advantages and drawbacks with regards to the other main already proposed NoC approaches and we prove its feasibility on examples through the simulations. Performance evaluation and implementation results are also given.     

A scalable publish/subscribe system for large mobile ad hoc networks

Since nodes that compose mobile ad hoc networks (MANETs) does not have any prior knowledge about other nodes in many cases, the publish/subscribe communication paradigm that has the decoupling and asynchrony properties can be useful to share information between nodes. Existing publish/subscribe services for MANETs can be categorized into document flooding (DF), destination-based routing (DBR), and content-based routing (CBR). Although those approaches may work well when the size of network is small, all of them suffer from the performance decline as the size of the network increases. In this paper, we compare those approaches, and then propose a scalable publish/subscribe communication scheme in large MANETs by combining DF and CBR hierarchically. Our approach is to cluster all nodes in networks and to exploit CBR and DF for the intra- and inter-cluster communication, respectively. By using this approach, we can effectively utilize benefits of both approaches. Then, we present performance evaluation results which validate our idea with respect to system performance and scalability.     

基于邮箱的移动Agent通信机制的改进算法

在基于邮箱的移动Agent通信机制上提出一种改进算法,通过移动Agent留下特殊的、具有一定智能性的邮箱来转发消息,实现移动Agent高效和可靠的消息传输。进一步提高了通信效率而且减小了由于邮箱所在节点出现故障而造成的损失。     

企业内部分布式存储高效扩展机制研究

在研究文件存储基础设备与技术发展的基础上,提出一种可高效扩展的分布式存储机制,将企业中已有的服务器和存储设备作为分布式存储的存储单元,将文件作为存储对象,建立一种高效率甚至是零等待时间的可以随时扩展或减少存储单元的分布式存储机制。企业中存在的服务器和存储设备较多时,利用该分布式存储机制后存储性能会得到较大的提升,管理人员文件管理的劳动强度将大大降低。重点是能够帮助企业充分利用原有的服务器和存储设备,减少更新换代的一次性大量投入。