Distribution by Scientific Domains
Distribution within Engineering

Kinds of Subsystems

  • second subsystem

  • Selected Abstracts

    A peer-to-peer IPTV service architecture for the IP multimedia subsystem

    A. Bikfalvi
    Abstract During these last years the Internet Protocol Television (IPTV) service and the different peer-to-peer (P2P) technologies have generated an increasing interest for the developers and the research community that find in them the solution to deal with the scalability problem of media streaming and reducing costs at the same time. However, despite of the benefits obtained in Internet-based applications and the growing deployment of commercial IPTV systems, there has been a little effort in combining them both. With the advent of the next-generation-network platforms such as the IP Multimedia Subsystem (IMS), which advocates for an open and inter-operable service infrastructure, P2P emerges as a possible solution in situations where the traditional streaming mechanisms are not possible or not economically feasible. In this paper, we propose an IPTV service architecture for the IMS that combines a centralized control layer and a distributed, P2P-like, media layer that relies on the IMS devices or peers located in the customers' premises to act as streaming forwarding nodes. We extend the existing IMS IPTV standardization work that has already been done in 3GPP and ETSI TISPAN in order to require a minimum number of architectural changes. The objective is to obtain a system with a similar performance to the one in currently deployed systems and with the flexibility of P2P. One of the main challenges is to achieve comparable response times to user actions such as changing and tuning into channels, as well as providing a fast recovery mechanism when streaming nodes leave. To accomplish this we introduce the idea of foster peers as peers having inactive multimedia sessions and reserved resources. These peers are on stand-by until their functionality is required and at that moment, they are able to accept downstream peers at short notice for events requiring urgent treatment like channel changing and recovery. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Application creation for IMS systems through macro-enablers and Web 2.0 technologies

    Anne Y. Lee
    Rapid creation of an unlimited number of innovative new applications has been a promise of the IP Multimedia Subsystem (IMS) from the beginning. However, over the years, attention has been paid more to the development of the IMS foundation than methods for the IMS services factory,which is as it should be. The time has come to now address applications creation. This paper describes a way to enable carriers, third-party application developers, and the public to quickly produce new applications using IMS building blocks and application frameworks as well as Web 2.0 technologies and support for IMS + Internet applications mashups. IMS building blocks and application frameworks are macro application enablers. © 2010 Alcatel-Lucent. [source]

    Securing IMS against novel threats

    Stefan Wahl
    Fixed mobile convergence (FMC) based on the 3GPP IP Multimedia Subsystem (IMS) is considered one of the most important communication technologies of this decade. Yet this all-IP-based network technology brings about the growing danger of security vulnerabilities in communication and data services. Protecting IMS infrastructure servers against malicious exploits poses a major challenge due to the huge number of systems that may be affected. We approach this problem by proposing an architecture for an autonomous and self-sufficient monitoring and protection system for devices and infrastructure inspired by network intrusion detection techniques. The crucial feature of our system is a signature-less detection of abnormal events and zero-day attacks. These attacks may be hidden in a single message or spread across a sequence of messages. Anomalies identified at any of the network domain's ingresses can be further analyzed for discriminative patterns that can be immediately distributed to all edge nodes in the network domain. © 2009 Alcatel-Lucent. [source]

    Converged network common charging controller function

    Xiang Yang Li
    With the emergence of converged networks, circuit switched (CS), packet switched (PS), and IP Multimedia Subsystem (IMS) domains and application servers (AS) are now merging to combine all kinds of services, business modes, and network architectures. This can cause chaos among various charging mechanisms within the networks. This paper presents a common charging controller function (CCCF) between the charging trigger function (CTF) of individual network elements (NEs) and the charging system. The CCCF operates with the common NE-independent charging control layer to serve various network elements in CS, PS, and IMS domains and application servers. It also simplifies NE-dependent CTFs for accounting metrics collection (AMC), regardless of whether the charging mechanisms are online or offline. The CCCF maintains a single charging characteristic database that stores the charging mechanism of each subscriber's service usage and forwards subscriber accounting data to the charging systems. By including the CCCF in networks, the IMS and pre-IMS charging systems for existing and new customers can be integrated without replacing deployed products, resulting in significant cost savings for telecommunications vendors and customers. © 2008 Alcatel-Lucent. [source]

    An analysis of capital expenses and performance trade-offs among IMS CSCF deployment options

    Anne Lee
    Service providers around the world are deploying or planning to deploy the IP Multimedia Subsystem (IMS) in their core networks. IMS allows the delivery of new multimedia applications that can enhance the user's experience and bring in new revenue for the operators. These operators are now faced with deciding how to best deploy the various IMS functional elements in their networks. In this paper, the authors provide a survey of the various options available to the operators and present an analysis of some of those deployment options. In particular, the paper addresses questions around the advantages and disadvantages of centralizing or distributing control functions such as the call session control function (CSCF) in terms of capital expenditure (CAPEX) costs and latency trade-offs. Without the proper deployment strategy, there can be major differences in the overall cost of the network and therefore it is important to perform such an analysis. Initial recommendations and general observations are given that can assist network planners and operators to more efficiently develop an IMS deployment strategy. Further analysis and study that includes operational expenditure (OPEX) costs should also be factored into the final decision. © 2008 Alcatel-Lucent. [source]

    IMS network signaling peering: Challenges and proposal

    Jean-Philippe Joseph
    IP Multimedia Subsystem (IMS) network peering is a key enabler that will help accelerate deployment of next-generation IMS-based networks. Today's early deployments of dispersed IMS networks require public switched telephone network (PSTN)/public land mobile network (PLMN) bridges for network interconnection between IMS islands. The PSTN/PLMN bridging arrangement is inefficient, however, in that it results in unnecessary settlements for the carriers. It further impedes the implementation of rich multimedia and Voice over IP (VoIP)-related services that require end-to-end Internet Protocol (IP) connectivity. Last, it perpetuates the reliance on the existing PSTN/PLMN network for voice calls among subscribers served by different IMS-based carriers. This paper analyzes in detail the IMS peering challenges from the perspective of Session Initiation Protocol (SIP) signaling peering. It discusses issues related to the routing of SIP messages, and addressing, address resolution, and discovery of peering points for IMS signaling peering. It further establishes that a new routing algorithm is needed that will allow signaling peering points to dynamically discover the "best" transit network among others for reaching a destination. In closing, it presents a high-level IMS signaling routing process that includes, among other benefits, support for number portability as a key function for inter-carrier IMS peering. © 2008 Alcatel-Lucent. [source]

    Advanced IMS client supporting secure signaling

    Ramana Isukapalli
    With recent advances in core and access networks and the availability of increased bandwidth and sophisticated devices for end users, there is an increased demand for client applications running on mobile devices, such as laptops and handheld devices, to support real time applications like Voice over Internet Protocol (VoIP) and streaming video, apart from traditional applications like web browsing. This paper presents a prototype IP Multimedia Subsystem (IMS) client, which serves as a VoIP client to set up calls between Internet Protocol (IP) devices and interworks with circuit-switched networks to deliver calls to public switched telephone network (PSTN) phones. It implements supplementary services (including call waiting, call transfer, and call forwarding); supports multimedia ringing, short message service/multimedia messaging service (SMS/MMS), audio/video conferencing, and peer-to-peer video; and it can deliver a call to a user (as opposed to a device) by simultaneously ringing multiple devices registered by the user. Further, to address various security concerns, the client supports Hypertext Transfer Protocol (HTTP) digest authentication using Message Digest 5 (MD5) cryptographic function authentication and key agreement (AKA) and can create secure tunnels to the core network using IP security (IPsec). © 2008 Alcatel-Lucent. [source]

    Blending telephony and IPTV: Building the TV-link service package using the Alcatel-Lucent Service BrokerÔ

    Andre Beck
    This paper discusses the design and implementation of blended services, composite services whose base component services interact within a common control structure. The paper focuses on blended services that combine aspects of Internet Protocol television (IPTV) and IP Multimedia Subsystem, (IMS)-based telephony services and, in particular, focuses on a service that blends TV viewing and telephone call-handling functions. If a subscriber to this service receives a telephone call while watching TV, the caller ID is displayed on the subscriber's TV screen and the subscriber can signal call control instructions using the set-top box remote control. In this service blend, functions from each base service are coordinated with actions in the other. The mechanism allowing this service is an information channel that allows status and control information to move between the subscriber's set-top box and the IMS system. The services described in this paper are built upon a software foundation called the Alcatel-Lucent Service BrokerÔ platform, a platform that has unique capabilities to support such an information channel and to serve as the gateway between IMS and digital TV. This foundation offers service developers a set of important functions for the creation of blended services. Specifically, the Alcatel-Lucent Service Broker offers a means of controlling the invocation of base services, a means of communicating through different protocols, and support for large-scale deployment and for service customization. © 2007 Alcatel-Lucent. [source]

    Provisioning in complex networks

    Ganesan Radhakrishnan
    IP Multimedia Subsystem (IMS) solutions emphasize services including all-Internet Protocol (IP) voice, data, video, multimedia, and other user-centric services. IMS applications allow network convergence among wireline, wireless, and packet networks and interaction of services in disparate, multivendor, multitechnology networks. This increased level of sophistication leads to increased operational complexity and underscores the need for a unified provisioning system to minimize the overhead of managing network data. This paper outlines a scalable, distributed, provisioning framework for disparate data networks. It examines the current approaches to provisioning and their shortcomings in dealing with disparate data. At a fundamental level, it views provisioning as two distinct problems of data management and process modeling. It depicts a unifying framework, by separating data management from the application that provisions the data, leading to data-model independence. It shows that unified provisioning requires the support of many distinct technologies including federated data management, software component framework, distributed computing framework, and formalisms for describing behavior. © 2007 Alcatel-Lucent. [source]

    End-to-end availability considerations for services over IMS

    Abhaya Asthana
    Lucent IP Multimedia Subsystem (IMS) architecture provides an open framework for multimedia applications that support blended text, voice, and video services. Providing objectives for service downtime and failure rates, which reflect the end customer perspective, can be used to drive corrective and preventive action that better satisfy end customer expectations. However, the frameworks and techniques to do this on an end-to-end basis for network solutions of the complexity and size of IMS are not well established. In this paper we address the questions of specifying, estimating, and verifying the end-to-end availability for services over IMS. The purpose of this paper is to present a framework for establishing availability requirements and service failure rate metrics, and for performing "end-to-end" service downtime analysis. The framework can be used to guide network design and evaluate end-to-end performance in the field. © 2006 Lucent Technologies Inc. [source]

    Optimal availability and security for IMS-based VoIP networks

    Himanshu Pant
    Consumers are continuously looking for ways of improving their productivity, simplifying their tasks, and streamlining communications both domestically and globally. This has resulted in the need to support different applications and thus the ongoing process of migrating many network services from traditional circuit-switched networks to Internet Protocol (IP) to converged networks. The circuit-switched public switched telephone network (PSTN) was a closed network where cyber-security threats were not amajor issue. With the advent of converged networks and IP-based services, service providers, government, and enterprises are concerned about the growing security threat. The new networks and equipment will be subject to many types of threats and their vulnerabilities may expose mission critical applications and infrastructure to risk. Realization of these threats can lead to service outage. Today's communications service provider must decide how to treat the effects of security breaches so as to minimize service downtime. This paper highlights amethodology, with examples to identify the effect of security-related failures and the critical design factors to be considered when modeling service reliability. The ITU-T X.805 standard (now also ISO standard 18028-2), based on the Bell Labs security model, is used to evaluate potential high impact threats and vulnerabilities. The analysis uses the Bell Labs domain technique known as security domain evaluation. One of the critical outputs provides a prioritized understanding of the threats the network is exposed to and the vulnerabilities in the security architecture. The next step in themethodology includes incorporating the threats (vulnerabilities) identified in a reliability model and quantifying the corresponding service degradation. In this paper, these concepts are applied to IP Multimedia Subsystem (IMS)-based VoIP (Voice over IP) networks. Using reliability metrics, our analysis shows that reliability models are optimistic if we do not consider security. We demonstrate how reliability models can be enhanced to take security issues into account and that the X.805 standard can be used to identify the security threats. Finally, the model shows themitigation in downtime by including intrusion-tolerance features in the product and network design. Consideration of security-caused downtimewill lead to increased focus on preventing security vulnerabilities that can lead to service outages and also allow service providers to save on maintenance costs. © 2006 Lucent Technologies Inc. [source]

    SIP message prioritization and its applications

    Harold Batteram
    Session Initiation Protocol (SIP) signaling is an integral part of the IP Multimedia Subsystem (IMS) to support services such as Voice over IP (VoIP), multimedia sessions, presence, and instant messaging (IM). All of these services share a common SIP signaling infrastructure. In spite of careful network engineering, SIP network elements may experience high-load situations, in which SIP messages may experience too much delay or even get dropped. This paper addresses how such undesired high-load situations can be handled effectively by introducing a message prioritization mechanism in SIP servers. To validate the mechanism, it has been implemented in a highperformance JAIN*-SIP-compliant Java* SIP stack. This SIP stack incorporates several other innovations, such as a very efficient SIP message parser, and it can be used for a variety of SIP-based applications. Its design enables service providers to define custom message prioritization and rejection strategies based on SIP message characteristics, system state, and statistics. Measurements show that high-priority emergency messages can indeed be serviced without significant delay or loss in a high-load situation. The concept of and techniques for SIP prioritization are the subjects of a Lucent Technologies patent application. © 2006 Lucent Technologies Inc. [source]

    Friends night out,A working prototype of a blended lifestyle service enabled through IMS

    Tung Ching Chiang
    This letter describes the design and implementation of a prototype application intended to demonstrate how the IP Multimedia Subsystem (IMS) platform could be used to create blended services that help enhance a user's lifestyle. Communication applications (e.g., group instant messaging and voice conferencing) are blended with collaboration services (e.g., shared Webbrowsing and shared streaming video) and location-based services to create a compelling scenario that makes planning a night out with friends both convenient and fun. Several IMS components and protocols are used to achieve the blending. A seamless user interface is created through the use of an integrated Session Initiation Protocol (SIP) client and a unified graphical user interface (GUI). This prototype, which is being showcased in major tradeshows around the world, is serving as a foundation for planning new features for Lucent Technologies' IMS portfolio. © 2006 Lucent Technologies Inc. [source]

    Seamless mobility across IMS and legacy circuit networks

    Maria R. G. Azada
    The growing desire of network providers to introduce support for voice over IP (VoIP) has created interesting challenges in the area of interoperability with existing wireless circuit networks. The 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2) standards have defined the IP Multimedia Subsystem (IMS) as the platform for convergence. By definition, IMS is access agnostic; it provides services and features through a common core network, regardless of the means of transport. However, the IMS standards are just beginning to address the challenges associated with interworking with existing cellular circuit networks. Achieving seamless mobility involves supporting both roaming and handoff between networks. This paper discusses the issues involved in providing seamless mobility for subscribers across the packet and circuit domains and proposes network-based solutions. © 2006 Lucent Technologies Inc. [source]

    Subscriber data management in IMS networks

    Daniel F. Lieuwen
    Next-generation communication services will be driven by increasingly rich and distributed subscriber information. Current wireless networks have evolved such that subscriber information now resides in various elements (e.g., home location register [HLR], prepay, voice mail, short message, and location determination systems). Convergence with the Internet promises significantly more personal information, such as presence, calendars, address books, buddy lists, pictures, and video. The home subscriber server (HSS) in the IP Multimedia Subsystem (IMS) architecture provides centralized storage for subscriber data. However, some application servers will also have their own subscriber data. As the quantity and variety of applications grow, it will become increasingly useful to provide unified views of subscriber data both within a network and across networks. The Lucent DatagridÔ software provides a telecom-targeted data integration capability, so that applications can use a logical "single-point-of-access" for user profile information inside a service provider's network. © 2006 Lucent Technologies Inc. [source]

    Service capability interaction management in IMS using the Lucent Service BrokerÔ product

    Kristin F. Kocan
    The 3rd Generation Partnership Project/3rd Generation Partnership Project 2 (3GPP/3GPP2) designates the service capability interaction manager (SCIM) as a functional component in the IP Multimedia Subsystem (IMS). This paper focuses on how the Lucent Service BrokerÔ product has been designed and how it would be deployed to perform as a SCIM in an IMS network. We discuss the challenges in managing service capability interaction and providing blended services that are encountered in IMS and show how Lucent Service Broker flexibility is needed to accommodate the breadth of challenges. We describe how the internal structure of the Lucent Service Broker and its application programming interface (API) offer this flexibility while minimizing the effort involved in adding new SCIM logic. We also demonstrate how the Lucent Service Broker may be used to marshal IMS application resources on behalf of revenue-generating applications in various usage scenarios. © 2006 Lucent Technologies Inc. [source]

    Assessing Children's Emotional Security in the Interparental Relationship: The Security in the Interparental Subsystem Scales

    CHILD DEVELOPMENT, Issue 2 2002
    Patrick T. Davies
    Guided by the emotional security hypothesis, this study reports on the development of a new self-report measure that assesses children's strategies for preserving emotional security in the context of interparental conflict. Participants were 924 sixth, seventh, and eighth graders and a subset of their mothers, fathers, and teachers. Exploratory and confirmatory factor analyses of the Security in the Interparental Subsystem (SIS) Scale supported a seven-factor solution, corresponding well to the three component processes (i.e., emotional reactivity, regulation of exposure to parent affect, and internal representations) outlined in the emotional security hypothesis. The SIS subscales demonstrated satisfactory internal consistency and test,retest reliability. Support for the validity of the SIS Scale is evidenced by its significant links with parent reports of children's overt reactivity to conflict, children's responses to interparental conflict simulations 6 months later, and children's psychological maladjustment and experiential histories with interparental conflict across multiple informants (i.e., child, mother, father, and teacher). Results are discussed in the context of developing recommendations for use of the SIS and advancing the emotional security hypothesis. [source]

    Policy Subsystems and Regimes: Organized Interests and Climate Change Policy

    Shannon K. Orr
    This research is an examination of the role of organized interests in international climate change policy formation. Systematic survey results are used to demonstrate that organized interests actually engage in the same activities in both the international and domestic arenas. This research demonstrates that the climate change negotiations can be characterized as both a policy subsystem and an international regime. It is further argued that these two concepts are in fact highly analogous, thereby facilitating new cross-discipline research opportunities. The research is based on a web survey of organized interests accredited by the United Nations Framework Convention on Climate Change (UNFCCC), and on interviews and field research at the 8th Conference of the Parties of the UNFCCC in New Delhi, India. [source]

    The Dynamics of Incrementalism: Subsystems, Politics, and Public Lands

    Robert S. Wood
    A host of research has been produced in the decade since Baumgartner and Jones' theory of punctuated equilibrium first drew attention to the dynamics of policy change over time. Much of this research follows a topic across time, highlighting the shift from negative to positive feedback as challengers push an issue from subsystem to institutional level. Far less attention has been paid to the periods between major punctuations, neglecting key questions about whether incremental periods reflect an absence of challengers or the successful defense of established subsystem interests. This research is a comparison of policy change across two segments of environmental policy. The breakup of the timber subsystem was a clear victory for environmentalists, yet these same actors have been largely unsuccessful at dislodging established grazing interests. These findings highlight the strategic value of venue shifting for bypassing entrenched interests and illustrate the potential for successful challenges to occur in judicial venues. [source]

    Decentralized Parametric Damage Detection Based on Neural Networks

    Zhishen Wu
    In this paper, based on the concept of decentralized information structures and artificial neural networks, a decentralized parametric identification method for damage detection of structures with multi-degrees-of-freedom (MDOF) is conducted. First, a decentralized approach is presented for damage detection of substructures of an MDOF structure system by using neural networks. The displacement and velocity measurements from a substructure of a healthy structure system and the restoring force corresponding to this substructure are used to train the decentralized detection neural networks for the purpose of identifying the corresponding substructure. By using the trained decentralized detection neural networks, the difference of the interstory restoring force between the damaged substructures and the undamaged substructures can be calculated. An evaluation index, that is, relative root mean square (RRMS) error, is presented to evaluate the condition of each substructure for the purpose of health monitoring. Although neural networks have been widely used for nonparametric identification, in this paper, the decentralized parametric evaluation neural networks for substructures are trained for parametric identification. Based on the trained decentralized parametric evaluation neural networks and the RRMS error of substructures, the structural parameter of stiffness of each subsystem can be forecast with high accuracy. The effectiveness of the decentralized parametric identification is evaluated through numerical simulations. It is shown that the decentralized parametric evaluation method has the potential of being a practical tool for a damage detection methodology applied to structure-unknown smart civil structures. [source]

    Toward replication in grids for digital libraries with freshness and correctness guarantees

    Fuat Akal
    Abstract Building digital libraries (DLs) on top of data grids while facilitating data access and minimizing access overheads is challenging. To achieve this, replication in a Grid has to provide dedicated features that are only partly supported by existing Grid environments. First, it must provide transparent and consistent access to distributed data. Second, it must dynamically control the creation and maintenance of replicas. Third, it should allow higher replication granularities, i.e. beyond individual files. Fourth, users should be able to specify their freshness demands, i.e. whether they need most recent data or are satisfied with slightly outdated data. Finally, all these tasks must be performed efficiently. This paper presents an approach that will finally allow one to build a fully integrated and self-managing replication subsystem for data grids that will provide all the above features. Our approach is to start with an accepted replication protocol for database clusters, namely PDBREP, and to adapt it to the grid. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Temperature perception and nociception

    Barry G. Green
    Abstract The specificity theory of somesthesis holds that perceptions of warmth, cold, and pain are served by separate senses. Although no longer accepted in all its details, the theory's basic assumptions of anatomical and functional specificity have remained guiding principles in research on temperature perception and its relationship to pain. This article reviews the response characteristics of thermoreceptors, temperature-sensitive nociceptors, and their associated pathways in the context of old and new perceptual phenomena, most of which cannot be satisfactorily explained by the specificity theory. The evidence indicates that throughout most of the perceptual range, temperature sensitivity depends upon coactivation of, and interactions among, thermal and nociceptive pathways that are composed of both specific "labeled lines" and nonspecific, multimodal fibers. Adding to this complexity is evidence that tactile stimulation can influence the way in which thermal stimulation is perceived. It is argued that thermoreception is best defined as a functional subsystem of somesthesis that serves the very different and sometimes conflicting demands of thermoregulation, protection from thermal injury, and haptic perception. © 2004 Wiley Periodicals, Inc. J Neurobiol 61: 13,29, 2004 [source]

    The ancestral complement system in sea urchins

    L. Courtney Smith
    Summary: The origin of adaptive immunity in the vertebrates can be traced to the appearance of the ancestral RAG genes in the ancestral jawed vertebrate; however, the innate immune system is more ancient. A central subsystem within innate immunity is the complement system, which has been identified throughout and seems to be restricted to the deuterostomes. The evolutionary history of complement can be traced from the sea urchins (members of the echinoderm phylum), which have a simplified system homologous to the alternative pathway, through the agnathans (hagfish and lamprey) and the elasmobranchs (sharks and rays) to the teleosts (bony fish) and tetrapods, with increases in the numbers of complement components and duplications in complement pathways. Increasing complexity in the complement system parallels increasing complexity in the deuterostome animals. This review focuses on the simplest of the complement systems that is present in the sea urchin. Two components have been identified that show significant homology to vertebrate C3 and factor B (Bf), called SpC3 and SpBf, respectively. Sequence analysis from both molecules reveals their ancestral characteristics. Immune challenge of sea urchins indicates that SpC3 is inducible and is present in coelomic fluid (the body fluids) in relatively high concentrations, while SpBf expression is constitutive and is present in much lower concentrations. Opsonization of foreign cells and particles followed by augmented uptake by phagocytic coelomocytes appears to be a central function for this simpler complement system and important for host defense in the sea urchin. These activities are similar to some of the functions of the homologous proteins in the vertebrate complement system. The selective advantage for the ancestral deuterostome may have been the amplification feedback loop that is still of central importance in the alternative pathway of complement in higher vertebrates. Feedback loop functions would quickly coat pathogens with complement leading to phagocytosis and removal of foreign cells, a system that would be significantly more effective than an opsonin that binds upon contact as a result of simple diffusion. An understanding of the immune response of the sea urchin, an animal that is a good estimator of what the ancestral deuterostome immune system was like, will aid us in understanding how adaptive immunity might have been selected for during the early evolution of the vertebrates and how it might have been integrated into the pre-existing innate immune system that was already in place in those animals. The authors are grateful to Drs Sham Nair and Paul Gross for their critique of the manuscript and helpful suggestions. This work was supported by the National Science Foundation (MCB 9603086). [source]

    Adaptive backstepping control for a class of time delay systems with nonlinear perturbations

    Chang-Chun Hua
    Abstract The sliding mode control method has been extensively employed to stabilize time delay systems with nonlinear perturbations. Although the resulting closed-loop systems have good transient and steady-state performances, the designed controllers are dependent on the time delays. But one knows that it is difficult to obtain the precise delay time in practical systems, especially when it is time varying. In this paper, we revisit the problem and use the backstepping method to construct the state feedback controller. First, a coordinate transformation is used to obtain a cascade time delay system. Then, a linear virtual control law is designed for the first subsystem. The memoryless controller is further constructed based on adaptive method for the second subsystem with the uncertainties bounded by linear function. By choosing new Lyapunov,Krasovskii functional, we show that the system state converges to zero asymptotically. Via the proposed approach, we also discuss the case that the uncertainties are bounded by nonlinear functions. Finally, simulations are done to verify the effectiveness of the main results obtained. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Mobile-initiated network-executed SIP-based handover in IMS over heterogeneous accesses

    Wei-Kuo Chiang
    Abstract The services of next generation networks are envisioned to be potentially capable of seamless mobility in spite of the heterogeneity in underlying access technologies. It is undoubted that to accomplish seamless services across heterogeneous networking environments gets harder in case of simultaneous mobility. In this article, we propose a mobile-initiated network-executed (MINE) session initial protocol (SIP)-based handover mechanism to facilitate simultaneous mobility in IP multimedia subsystem over heterogeneous accesses. The novelty of the proposed approach is that no changes are required to the existing network infrastructure since handover decision is fully made by the mobile host (MH) and handover execution is performed by a new-added application server called mobility server (MS). When the MH decides to initiate a handover and obtains a new IP address, it will send a SIP Publish message to trigger the MS to carry out the handover execution. With the network-executed design of the MINE, the MS can perform third-party registration for security re-association and third-party call control for session re-establishment in parallel. Moreover, the Master,Slave Determination procedures derived from H.245 are used in the MS to handle fairly the racing conditions resulting from simultaneous mobility such that redundant message flows are eliminated. Mathematical analyses present that the MINE can shorten the handover latency and reduce power consumption, as observed from a comparison with the integrated solution of an optimized macro-mobility mechanism and a receiver-side simultaneous mobility approach. Copyright © 2010 John Wiley & Sons, Ltd. [source]

    An effective IPv4,IPv6 translation mechanism for SIP applications in next generation networks

    Whai-En Chen
    Abstract In a next generation network, the IPv6-enabled IP multimedia subsystem (IMS) network may connect to an IPv4 network. When an IPv4/IPv6 dual-stack user equipment (UE) initiates a call by sending an IPv6 SIP INVITE message to an IPv4-only user agent (UA), the call cannot be established correctly. To resolve this problem, the IMS-application layer gateway solution, the redirect solution, and the interactive connectivity establishment solution have been proposed. In this paper, we propose an effective solution where only the IPv6 INVITE message is translated into an IPv4 INVITE message. Upon receipt of the IPv4 200 OK message replied from the IPv4-only UA, the dual-stack UE learns that the correspondent UA supports IPv4-only and utilizes IPv4 instead of IPv6 to send the subsequent SIP messages and real-time transport protocol (RTP) packets. The proposed solution is compared with the existing solutions in terms of network node modification, call setup complexity, and RTP transmission latency. Our study indicates that the proposed solution outperforms the other three solutions in the call setup and the RTP transmission. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    A peer-to-peer IPTV service architecture for the IP multimedia subsystem

    A. Bikfalvi
    Abstract During these last years the Internet Protocol Television (IPTV) service and the different peer-to-peer (P2P) technologies have generated an increasing interest for the developers and the research community that find in them the solution to deal with the scalability problem of media streaming and reducing costs at the same time. However, despite of the benefits obtained in Internet-based applications and the growing deployment of commercial IPTV systems, there has been a little effort in combining them both. With the advent of the next-generation-network platforms such as the IP Multimedia Subsystem (IMS), which advocates for an open and inter-operable service infrastructure, P2P emerges as a possible solution in situations where the traditional streaming mechanisms are not possible or not economically feasible. In this paper, we propose an IPTV service architecture for the IMS that combines a centralized control layer and a distributed, P2P-like, media layer that relies on the IMS devices or peers located in the customers' premises to act as streaming forwarding nodes. We extend the existing IMS IPTV standardization work that has already been done in 3GPP and ETSI TISPAN in order to require a minimum number of architectural changes. The objective is to obtain a system with a similar performance to the one in currently deployed systems and with the flexibility of P2P. One of the main challenges is to achieve comparable response times to user actions such as changing and tuning into channels, as well as providing a fast recovery mechanism when streaming nodes leave. To accomplish this we introduce the idea of foster peers as peers having inactive multimedia sessions and reserved resources. These peers are on stand-by until their functionality is required and at that moment, they are able to accept downstream peers at short notice for events requiring urgent treatment like channel changing and recovery. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Potential performance bottleneck in Linux TCP

    Wenji Wu
    Abstract Transmission control protocol (TCP) is the most widely used transport protocol on the Internet today. Over the years, especially recently, due to requirements of high bandwidth transmission, various approaches have been proposed to improve TCP performance. The Linux 2.6 kernel is now preemptible. It can be interrupted mid-task, making the system more responsive and interactive. However, we have noticed that Linux kernel preemption can interact badly with the performance of the networking subsystem. In this paper, we investigate the performance bottleneck in Linux TCP. We systematically describe the trip of a TCP packet from its ingress into a Linux network end system to its final delivery to the application; we study the performance bottleneck in Linux TCP through mathematical modelling and practical experiments; finally, we propose and test one possible solution to resolve this performance bottleneck in Linux TCP. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Analysis of the current methods used to size a wind/hydrogen/fuel cell-integrated system: A new perspective

    H. G. Geovanni
    Abstract As an alternative to the production and storage of intermittent renewable energy sources, it has been suggested that one can combine several renewable energy technologies in one system, known as integrated or hybrid system, that integrate wind technology with hydrogen production unit and fuel cells. This work assesses the various methods used in sizing such systems. Most of the published papers relate the use of simulation tools such as HOMER, HYBRID2 and TRNSYS, to simulate the operation of different configurations for a given application in order to select the best economic option. But, with these methods one may not accurately determine certain characteristics of the energy resources available on a particular site, the profiles of estimated consumption and the demand for hydrogen, among other factors, which will be the optimal parameters of each subsystem. For example, velocity design, power required for the wind turbine, power required for the fuel cell and electrolyzer and the storage capacity needed for the system. Moreover, usually one makes excessive use of bi-parametric Weibull distribution function to approximate the histogram of the observed wind to the theoretical, which is not appropriate when there are bimodal frequency distributions of wind, as is the case in several places in the world. A new perspective is addressed in this paper, based on general system theory, modeling and simulation with a systematic approach and the use of exergoeconomic analysis. There are some general ideas on the advantages offered in this method, which is meant for the implementation of wind/hydrogen/fuel cell-integrated systems and in-situ clean hydrogen production. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    On the analysis of some orbital contributions to the current density in circulenes

    Guglielmo Monaco
    Abstract According to the ipsocentric method, the current density stems from a sum of rotationally and translationally allowed transitions: translationally allowed transition are diatropic and rotationally allowed transition must be prevailingly paratropic. Applying this method to circulenes, we show that it can be used, together with simple Hückel theory, to design systems with localized currents on the rim. More importantly, we report the current density maps of coronene2+ and coronene2,. In these systems, a single rotational contribution gives both diatropic and paratropic circulations. This finding has been interpreted by a simple model based on the orbitals of the subsystem, which are the hub and the rim. It turns out that, in such cases, simple inspection of the Hückel orbitals is sufficient to predict the relative tropicities on the rim and the hub. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]