Vertical Handovers & IEEE 802.21

Seamless handover in wireless networks is to guarantee both service continuity and service quality. In WiMAX, providing scalability and quality of service for multimedia services during handover is a main challenge because of high latency and packet loss. In this paper, we created four scenarios using Qualnet 5.2 Network Simulator to analyze the hard handover functionality of WiMAX under different conditions. The scenarios such as Flag with 5 and 10 sec UCD and DCD interval values, Random mobility scenario and DEM scenario using 6 WiMAX Cells have been considered. This study is performed over the real urban area of JNU where we have used JNU map for scenarios 1, 2 and 3 but for scenario 4, the JNU terrain data has been used. Further, each BS of 6 WiMAX cell is connected to four nodes. All nodes of each scenario are fixed except Node 1. Node 1 is moving and performing the handover between the different BSs while sending and receiving real time traffics. Flag mobility model is used in Scenario 1, 2 and 4 to model the movement of the Node 1 while we use random mobility model in sceanrio3. 5 seconds time interval is used for Scenarios 1, 3, and 4 while 10 seconds time interval is used for scenario 2 to study the effect of management messages load on handover. Further, the statistical measures of handover performance of WiMAX in terms of number of handover performed, throughput, end-to-end delay, jitter, and packets dropped are observed and evaluated.

The Internet access paradigm is changing and a wide range of overlapping radio access technologies, such as WiMAX, Wi-Fi, 3GPP UMTS/LTE and DVB-H, will soon be available to most users and their multi-access devices. Therefore, novel mechanisms and protocols are needed to provide seamless mobility between different wireless access technologies. This paper presents novel handover procedures, based on media independent schemes, to address seamless mobility in heterogeneous environments. We propose an enhanced Media Independent Handover Framework (eMIHF), which extends IEEE 802.21 by allowing for efficient provisioning and activation of QoS resources in the target radio access technology during the handover preparation phase, and efficiently interacts with the mobility processes of different technologies employed. We evaluate eMIHF using the ns-2 simulator, and demonstrate that the proposed handover scheme provides seamless mobility, with low latency and no packet loss.

Envisioning a future where mobile terminals equipped with one or more network 9 devices are able to roam across wireless or wired networks, in a diverse macro and 10 micro wireless cells environment, requires the development of enhanced methods 11 to control IP based mobility. These methods should consider traditional terminal 12 mobility (mainly due to user movement) as well as mobility across heterogeneous 13 networks in the presence of semi-static users. For this to become reality, a cross layer 14 interaction is required starting from a potentially large diversity of layer two access 15 technologies up to the common IP layer, allowing the exchange of messages between 16 terminals and network components. Furthermore, traditional host mobility driven 17 concepts need to evolve, and include more stringent mobile operator requirements 18 in context of fully driven network controlled mobility. This paper presents and 19 evaluates a novel framework design, based on the IEEE 802.21 future standard, 20 encompassing network driven as well as host driven mobility 1 . This paper evaluates 21 signaling aspects, algorithm design and performance issues. 22 IP Mobility has been widely explored in the research community. IETF 2 pro-26 tocols, such as [1], [2], [3], [4] and their extensions or optimizations [5], [6], are 27 becoming mature and implementations are already available for deployment. 28 This is being fostered by large scale ambitions for future generation networks, 29 which will require synergy across multiple technology aspects [7]: liaisons be-30 tween standardization bodies are happening with increasing frequency. As 31 examples, 3GPP 3 (defining architecture reference scenarios for next genera-32 tion Mobile Operators networks), the WiMax forum 4 (defining the WiMax 33 mobile reference architecture) and the IEEE 5 802.21 working group (defining 34 standards for enhanced vertical handover strategies) are actively discussing 35 liaisons with IETF to agree on a common set of requirements to ensure the 36 compatibility between architectures and protocols for mobility [8], [9], [10]. In 37 other words, while IETF mobility protocols use the IP layer as convergence 38

AbstractThe primary focus of this review is tropical-extratropical interactions and especially the issues involved in determining the response of the extratropical atmosphere to tropical forcing associated with sea surface temperature (SST) anomalies. The review encompasses observations, empirical studies, theory and modeling of the extratropical teleconnections with a focus on developments over the Tropical Oceans-Global Atmosphere (TOGA) decade and the current state of understanding. In the tropical atmosphere, anomalous SSTs force anomalies in convection and large-scale overturning with subsidence in the descending branch of the local Hadley circulation. The resulting strong upper tropospheric divergence in the tropics and convergence in the subtropics act as a Rossby wave source. The climatological stationary planetary waves and associated jet streams, especially in the northern hemisphere, can make the total Rossby wave sources somewhat insensitive to the position of the tropical heating that induces them and thus can create preferred teleconnection response patterns, such as the Pacific-North American (PNA) pattern. However, a number of factors influence the dispersion and propagation of Rossby waves through the atmosphere, including zonal asymmetries in the climatological state, transients, and baroclinic and nonlinear effects. Internal midlatitude sources can amplify perturbations. Observations, modeling, and theory have clearly shown how storm tracks change in response to changes in quasi-stationary waves and how these changes generally feedback to maintain or strengthen the dominant perturbations through vorticity and momentum transports. The response of the extratropical atmosphere naturally induces changes in the underlying surface, so that there are changes in extratropical SSTs and changes in land surface hydrology and moisture availability that can feedback and influence the total response. Land surface processes are believed to be especially important in spring and summer. Anomalous SSTs and tropical forcing have tended to be strongest in the northern winter, and teleconnections in the southern hemisphere are weaker and more variable and thus more inclined to be masked by natural variability. Occasional strong forcing in seasons other than winter can produce strong and identifiable signals in the northern hemisphere and, because the noise of natural variability is less, the signal-to-noise ratio can be large. The relative importance of tropical versus extratropical SST forcings has been established through numerical experiments with atmospheric general circulation models (AGCMs). Predictability of anomalous circulation and associated surface temperature and precipitation in the extratropics is somewhat limited by the difficulty of finding a modest signal embedded in the high level of noise from natural variability in the extratropics, and the complexity and variety of the possible feedbacks. Accordingly, ensembles of AGCM runs and time averaging are needed to identify signals and make predictions. Strong anomalous tropical forcing provides opportunities for skillful forecasts, and the accuracy and usefulness of forecasts is expected to improve as the ability to forecast the anomalous SSTs improves, as models improve, and as the information available from the mean and the spread of ensemble forecasts is better utilized.AbstractThe primary focus of this review is tropical-extratropical interactions and especially the issues involved in determining the response of the extratropical atmosphere to tropical forcing associated with sea surface temperature (SST) anomalies. The review encompasses observations, empirical studies, theory and modeling of the extratropical teleconnections with a focus on developments over the Tropical Oceans-Global Atmosphere (TOGA) decade and the current state of understanding. In the tropical atmosphere, anomalous SSTs force anomalies in convection and large-scale overturning with subsidence in the descending branch of the local Hadley circulation. The resulting strong upper tropospheric divergence in the tropics and convergence in the subtropics act as a Rossby wave source. The climatological stationary planetary waves and associated jet streams, especially in the northern hemisphere, can make the total Rossby wave sources somewhat insensitive to the position of the tropical heating that induces them and thus can create preferred teleconnection response patterns, such as the Pacific-North American (PNA) pattern. However, a number of factors influence the dispersion and propagation of Rossby waves through the atmosphere, including zonal asymmetries in the climatological state, transients, and baroclinic and nonlinear effects. Internal midlatitude sources can amplify perturbations. Observations, modeling, and theory have clearly shown how storm tracks change in response to changes in quasi-stationary waves and how these changes generally feedback to maintain or strengthen the dominant perturbations through vorticity and momentum transports. The response of the extratropical atmosphere naturally induces changes in the underlying surface, so that there are changes in extratropical SSTs and changes in land surface hydrology and moisture availability that can feedback and influence the total response. Land surface processes are believed to be especially important in spring and summer. Anomalous SSTs and tropical forcing have tended to be strongest in the northern winter, and teleconnections in the southern hemisphere are weaker and more variable and thus more inclined to be masked by natural variability. Occasional strong forcing in seasons other than winter can produce strong and identifiable signals in the northern hemisphere and, because the noise of natural variability is less, the signal-to-noise ratio can be large. The relative importance of tropical versus extratropical SST forcings has been established through numerical experiments with atmospheric general circulation models (AGCMs). Predictability of anomalous circulation and associated surface temperature and precipitation in the extratropics is somewhat limited by the difficulty of finding a modest signal embedded in the high level of noise from natural variability in the extratropics, and the complexity and variety of the possible feedbacks. Accordingly, ensembles of AGCM runs and time averaging are needed to identify signals and make predictions. Strong anomalous tropical forcing provides opportunities for skillful forecasts, and the accuracy and usefulness of forecasts is expected to improve as the ability to forecast the anomalous SSTs improves, as models improve, and as the information available from the mean and the spread of ensemble forecasts is better utilized.

— Handover of calls between two BS is encountered frequently and the delay can occur during the process of handover. This delay is known as handover latency. A good handover decision model or algorithm should consider Handoff latency factor and it should be minimized. In this paper five MADM algorithms have been analyzed and compared for handover latency in heterogeneous network. The algorithms were simulated with varying number of attributes for various applications.

The development and deployment of several wireless
and cellular networks mean that users will demand to be always
connected as they move around. Mobile nodes will therefore have
several interfaces and connections will be seamlessly switched
among available networks using vertical handover techniques.
Proactive handover mechanisms can be combined with the
deployment of a number of location-based systems that provide
location information to a very high degree of accuracy in different
contexts. Furthermore, this new environment will also allow
contextual information such as user profiles as well as the
availability of local services to be combined to provide optimal
communications for mobile users. The goal of this paper is
therefore to explore the development of a comprehensive framework
for achieving optimal communication in heterogeneous
wireless environments using location and contextual information
to provide efficient handover mechanisms. Using location-based
techniques, it is possible to demonstrate that the Time Before
Handover as well as the Network Dwell Time can be accurately
estimated. These techniques are dependent on accurately estimating
the handover radius. This paper investigates how location and
context awareness can be used to estimate the best handover
radius. The paper also explores how such techniques may be
integrated into the Y-Comm architecture which is being used to
explore the development of future mobile networks. Finally, the
paper highlights the use of ontological techniques as a mechanism
for specifying and prototyping such systems.

In this era of emerging technologies, the main issue is to discover the appropriate neighbor access network during handoff mechanism for a mobile node. We require handover because in this heterogeneous environment, there can be several networks (Wi-Fi, WIMAX and UMTS) in a geographical area which are not so interoperable. For abiding the services we use Media Independent Information Service (MIIS) provided by IEEE 802.21 MIH standards to select the most suitable network. This study provides a brief overview of how the challenges associated with the handoff are solved by several proposed schemes. In the introduction, role of MIIS is comprehensively defined to represent its importance followed by issues associated with handoff. Then, it gives an overview of the latest research activities in this field, including all the problems faced during handoff process. The study concludes by giving a new hierarchical scheme presenting implementation of MIIS servers to significantly improve the mobility.

The continuous innovations and advances in both high-end mobile devices and wireless communication technologies have increased the users demand and expectations for anywhere, anytime, any device high quality multimedia applications provisioning. Moreover, the heterogeneity of the wireless network environment offers the possibility to the mobile user to select between several available radio access network technologies. However, selecting the network that enables the best user perceived video quality is not trivial given that in general the network characteristics vary widely not only in time but also depending on the user location within each network. In this context, this paper proposes a user location-aware reputation-based network selection solution which aims at improving the video delivery in a heterogeneous wireless network environment by selecting the best value network. Network performance is regularly monitored and evaluated by the currently connected users in different areas of each individual network. Based on the existing network performance-related information and mobile user location and speed, the network that offers the best support for video delivery along the user’s path is selected as the target network and the handover is triggered. The simulation results show that the proposed solution improves the video delivery quality in comparison with the case when a classic network selection mechanism was employed.

We propose in this paper a simulation implementation of Self-Organizing Networks (SON) optimization related to mobility load balancing (MLB) for LTE systems using ns-3 [1]. The implementation is achieved toward two MLB algorithms dynamically adjusting handover (HO) parameters based on the Reference Signal Received Power (RSRP) measurements. Such adjustments are done with respect to loads of both an overloaded cell and its cells' neighbours having enough available resources enabling to achieve load balancing. Numerical investigations through selected key performance indicators (KPIs) of the proposed MLB algorithms when compared with another HO algorithm (already implemented in ns-3) based on A3 event [2] highlight the significant MLB gains provided in terms global network throughput, packet loss rate and the number of successful HO without incurring significant overhead.

As wireless access technologies grow rapidly, the recent studies have focused on granting mobile users the ability of roaming across different wireless networks in a seamless manner thus offering seamless mobility. The different characteristics of each wireless technology with regards to QoS brought many
challenges for provisioning the continuous services  audio/video streaming) in a seamless way. In this paper, we intend to review the existing context-aware methods which offered solutions for service continuity. We looked at the types of context information used in each solution. Through this study, it is clear that context awareness plays a significant role in handover process in order to satisfy users demanding seamless services. Therefore, the goal of this paper is to compare the existing methods grouped as general, IMS based, and WLAN/WiMAX solutions in terms of several criteria, such as
interworking architecture, service continuity, and QoS provisioning.

With the foreseen major increase in video traffic over the coming years, the current Internet's design is being perceived as inefficient for handling the demanding flow of video over wireless access networks, populated by an ever increasing number of mobile terminals. The MEDIEVAL project aims to evolve the current Internet architecture to provide an optimized video support in all layers of the protocol stack. With its cross-layer approach, abstraction mechanisms such as IEEE802.21 will work as enablers between the different architecture modules. With the widespread diffusion of video being realized over multicast and broadcast channels for resource optimization, using 802.21 signalling to optimize handovers affecting groups of users will generate multiple messages to each individual terminal. In this article, we extend 802.21 to support multicast transport of its signalling, enabling more efficient group handover scenarios.

The MEDIEVAL project aims to leverage today’s Internet with thenecessary fabric to provide optimized video services in a mobile wireless world. It is expected that video traffic will surpass Peer-to-Peer (P2P) in volume in the coming years, and thus novel mechanisms and techniques need to be provided to better suit its unique requirements. This article describes the key functionalelements of the MEDIEVAL architecture, which provides a video-aware networking core coupled with abstracting interfaces which cater to service and access technology specific requirements, aiming to enable efficient video transport and novel video service development.

The Next Generation Internet will provide ubiquitous computing by the seamless operation of heterogeneous wireless networks. It will also provide support for quality-ofservice, QoS, fostering new classes of applications and will have a built-in multi-level security environment. A key requirement of this new infrastructure will be support for efficient vertical handover. Y-Comm is a new architecture that will meet the challenge of this new environment. This paper explores the design of efficient imperative handover mechanisms using the Y-Comm Framework. It first looks at different types of handovers, then examines the Y-Comm Framework and shows how Y-Comm maps unto current mobile infrastructure. It then explores support for different handover mechanisms using Y-Comm. Finally, it highlights the development of a new testbed to further investigate the proposed mechanisms.

handover performance plays a crucial role in ensuring the quality of real-time applications in WiMAX networks. In general, the total delay associated with the handover process can be divided into three category: i) link layer handover delay , ii) IP layer handover delay, iii) Security sub-layer handover delay , research shows that a large portion of the delay related to handover are actually comes from user authentication and network entry and re-entry , real-time applications such as VoIP and video streaming .require a minimum interruption for a suitable service , sadly the existing design of the handover scheme could not provide seamless safe connection , therefore the use of such application will be unlikely , in this paper we introduce an efficient design that can provide fast and secure communication especially over the subsequent handover , we named it FSSHO for short , in our proposal we consider the use the of a pre-authentication scheme and prior backhaul inter-communication , our design generate a minimum delay that is more than suitable for real-time application.  From our analytical comparison and simulation result we can see that our FSSHO approach achieves 72% improve over the standard and 38% improve over the enhanced scheme in [1]

In the current environment, network operators are trying to cope with the significant increase in data traffic by adopting different solutions to expand their network capacity. One solution would be the convergence of next generation wireless networks (e.g., HSDPA, LTE and WiMAX) which involve the closely interworking of the existing 2G/2.5G/3G networks with the new next generation networks in terms of handover and network selection. However, as a result, the diversification in mobile devices and the heterogeneity of the wireless environment make the seamless always best connectivity of the mobile users a challenge for the service providers.
To this extent, we propose RLoad a novel Reputation-based Load-balancing Network Selection Strategy for heterogeneous wireless environments built on top of the IEEE 802.21 Media Independent Handover (MIH) standard. The proposed solution makes use of a reputation-based mechanism to select the most appropriate set of networks for the mobile user and a load balancing mechanism to distribute the traffic load among the networks by making use of the Multipath TCP (MPTCP) protocol. Preliminary simulation results show the significant benefits of the proposed RLoad solution."

Vertical handover decision algorithm that is based on user preferences and coupled with Media Independent Handover (MIH) local triggers have not been explored much in the literature. We have developed a comprehensive cross-layer solution, called Vertical Handover Decision (VHOD) approach, which consists of three parts viz. mechanism for collecting and storing user preferences, Vertical Handover Decision (VHOD) algorithm and the MIH Function (MIHF). MIHF triggers the VHOD algorithm which operates on user preferences to issue handover commands to mobility management protocol. VHOD algorithm is an MIH User and therefore needs to subscribe events and configure thresholds for receiving triggers from MIHF. In this regard, we have performed experiments in WLAN to suggest thresholds for Link Going Down trigger. We have also critically evaluated the handover decision process, proposed Just-in-time interface activation technique, compared our proposed approach with prominent user centric appr...

As the use of global positioning system (GPS) has been popular, location and velocity information obtained from GPS has been used to assist the handover process. In this paper, for GPS-enabled mobile units, we propose a new handover scheme using an adaptive base station map. The adaptive base station map stores/updates the information on the base station, which could provide most stable services at the mobile unit's current location. In general, since users spend most of their time in a specific area such as near their companies, near their homes, or on their way to and from home, a very detailed base station map can be made for these areas within a short time. Therefore, it can be expected that the proposed scheme perform more effectively within the radius of the user's main activity.

Vertical handover decision algorithm that is based on user preferences and coupled with Media Independent Handover (MIH) local triggers have not been explored much in the literature. We have developed a comprehensive cross-layer solution, called Vertical Handover Decision (VHOD) approach, which consists of three parts viz. mechanism for collecting and storing user preferences, Vertical Handover Decision (VHOD) algorithm and the MIH Function (MIHF). MIHF triggers the VHOD algorithm which operates on user preferences to issue handover commands to mobility management protocol. VHOD algorithm is an MIH User and therefore needs to subscribe events and configure thresholds for receiving triggers from MIHF. In this regard, we have performed experiments in WLAN to suggest thresholds for Link Going Down trigger. We have also critically evaluated the handover decision process, proposed Just-in-time interface activation technique, compared our proposed approach with prominent user centric approaches and analyzed our approach from different aspects.

The significant developments in terms of both mobile computing device (e.g., smartphones, tablets, laptops, etc.) and the wireless communication technologies (e.g., LTE, LTE-Advanced, WiMAX, etc.), lead towards a converged heterogeneous wireless environment. In this context, the user will be facing the problem of selecting from a number of Radio Access Networks that differ in technology, coverage, pricing scheme, bandwidth, latency, etc. In order to provide high quality of service (QoS) to the user in this heterogeneous wireless environment, a network selection solution is required that will efficiently facilitate the vertical handover between different wireless access networks in a seamless manner. In this paper, we propose a reputation-based network selection solution which aims to select the best value network for the user. We propose a network profiling algorithm that used to compute the reputation of each of the available networks based on the joint collaboration of the users within the network. The network with the best reputation value is recommended for selection and handover.

Current mobile devices are equipped with multi-standard interfaces to fully utilize both the existing and the imminent  Public Land Mobile Network infrastructure.  This flexibility comes with significant energy consumption overheads at the mobile terminal side and thus, the adopted interface / network selection scheme, a.k.a. Vertical Handover mechanism, should be based on both Quality of Service oriented and energy-efficiency criteria.  This paper summarizes the current state of the art on energy-centric vertical handover algorithms, discusses weak aspects of existing approaches and presents a novel context-aware vertical handover framework towards energy-efficiency.  Rather than a pure energy-centric vertical handover scheme, this framework is a context-awareness enabler for energy-centric vertical handover decision making.

Vertical handover decision algorithm that is based on user preferences and coupled with Media Independent Handover (MIH) local triggers have not been explored much in the literature. We have developed a comprehensive cross-layer solution, called Vertical Handover Decision (VHOD) approach, which consists of three parts viz. mechanism for collecting and storing user preferences, Vertical Handover Decision (VHOD) algorithm and the MIH Function (MIHF). MIHF triggers the VHOD algorithm which operates on user preferences to issue handover commands to mobility management protocol. VHOD algorithm is an MIH User and therefore needs to subscribe events and configure thresholds for receiving triggers from MIHF. In this regard, we have performed experiments in WLAN to suggest thresholds for Link Going Down trigger. We have also critically evaluated the handover decision process, proposed Just-in-time interface activation technique, compared our proposed approach with prominent user centric appr...

International Journal of Wireless & Mobile Networks (IJWMN) is a bi monthly open access peer-reviewed journal that publishes articles which contribute new results in all areas of Wireless & Mobile Networks. The journal focuses on all technical and practical aspects of Wireless & Mobile Networks. The goal of this journal is to bring together researchers and practitioners from academia and industry to focus on advanced wireless & mobile networking concepts and establishing new collaborations in these areas.

Wireless access technologies have been extensively developed aiming to give users the ability to connect to their expected networks anytime, anywhere. This leads to an increment of the number of wireless interfaces integrated into a single mobile device, hence, it allows the device to be able to connect to multiple access networks. However, in some specific cases such as natural disasters, having an uncorrupted and timely information exchanging means is critical for affected victims to survive or to connect to the outside world. This is because the essential network infrastructures in these cases could be destroyed causing a large number of systems to stop working. In that cases, the victims need a heterogeneous communications network in which they can communicate, without a doubt, by using different wireless access technologies, i.e., Bluetooth or Wi-Fi. The network must also be able to smoothly change the access technologies, or called a vertical handover, to ensure QoS for ongoing applications. In addition, the network must have a mechanism to save energy. For these reasons, an SDN approach, which has been proposed in a previous work, is considered. The performance of the system has been validated by a set of experiments in a real testbed. The obtained results show that the proposed vertical handover can save at least 24.42 per cent of the energy consumed by the wireless communication. The handover delay with different UDP traffic is less than 150ms. Moreover, the network allows a device using Bluetooth to talk with another one using Wi-Fi over a heterogeneous connection where the end-to-end jitter is mainly below 20ms and the packet loss rate is as small as 0.2 per cent.

Vertical handover decision algorithm that is based on user preferences and coupled with Media Independent Handover (MIH) local triggers have not been explored much in the literature. We have developed a comprehensive crosslayer solution, called Vertical Handover Decision (VHOD) approach, which consists of three parts viz. mechanism for collecting and storing user preferences, Vertical Handover Decision (VHOD) algorithm and the MIH Function (MIHF). MIHF triggers the VHOD algorithm which operates on user preferences to issue handover commands to mobility management protocol. VHOD algorithm is an MIH User and therefore needs to subscribe events and configure thresholds for receiving triggers from MIHF. In this regard, we have performed experiments in WLAN to suggest thresholds for Link Going Down trigger. We have also critically evaluated the handover decision process, proposed Justintime interface activation technique, compared our proposed approach with prominent user centric approaches and analyzed our approach from different aspects. commercial networks subscription details and user preferences regarding network selection are application layer features. While moving, whenever a Mobile Node (MN) is in overlapping region, effective network selection becomes a task that requires intelligent decision making based upon selected information from multiple layers and therefore it openly speaks off the necessity of a crosslayer design .

One of the challenging issues in Next Generation Wireless Network (NGWN) is achieving seamless Vertical
Handover (VHO) while roaming between different technologies such as Wireless Fidelity (Wi- Fi),
Worldwide Interoperability for Microwave Access (WiMAX), Universal Mobile Telecommunications
System (UMTS) and Long Term Evolution (LTE). F or that the telecommunication operators will be
required to develop a strategy for interoperability of these different types of existing network to give the
best connection anywhere anytime for the Mobile Users (MUs).
To full these requirements we propose a new VHO approach that based on loose coupling internetworking
in conjunction with Mobile IPv4 ( MIPv4) under Media Independent Handover (MIH). Our objective is
develop a strategy for interoperability of different technologies and optimized the VHO decision. Our
proposed approach provides more exhaustive, high accurate and better performance compared with the
approaches proposed in the literature.

Following a recent upgrade, the Digital Video Broadcasting-Return Channel Satellite (DVB-RCS) standard sets up to support terminal mobility. In this scenario, integration with terrestrial systems becomes a primary concern to ensure network connectivity in urban areas. This article proposes an integrated satellite-terrestrial architecture for the provision of broadband services onboard high-speed trains, in which terrestrial cellular networks are seen as viable gap-fillers for discontinuous satellite coverage. We derive an analytical model of the hybrid DVB-RCS-cellular system by exploiting analogies between the mobility pattern predictability of LEO constellations and that of high-speed trains. Terminals whose QoS cannot be guaranteed by the satellite segment are proposed to temporarily divert the connections towards the terrestrial infrastructure, where available. Using an iterative approach based on the Erlang fixed-point approximation, we show performance improvements with respect to stand-alone satellite systems in terms of handover failure probability and overall resource utilization. The analytical model is also validated via our ns2-based DVB-RCS packet-level simulator. Detailed modelling of synchronization and signalling mechanisms confirms the accuracy of the analytical results, and shows that topology and mobility information can contribute to refine radio resource utilization optimality when used jointly.

Next generation networks will comprise di®erent wireless networks including cellular technologies, WLAN and indoor technologies. To support these heterogeneous environments, there is a need to consider a new design of the network infrastructure. Furthermore, this heterogeneous environment implies that future devices will need to roam between di®erent networks using vertical handover techniques. When a mobile user moves into a new foreign network, data con¯dentiality and mutual authentication between the user and the network are vital issues in this heterogeneous environment. This article deals with these issues by ¯rst examining the implication of moving towards an open architecture, and then looking at how current approaches such as the 3GPP, HOKEY and mobile ethernet respond to the new environment while trying to address the security issue. The results indicate that a new authentication and key agreement protocol is required to secure handover in this environment. Casper/FDR, is used in the analysis and development of the protocol. The proposed protocol has been proven to be successful in this heterogeneous environment. Keywords: authentication and key agreement protocol; secure vertical handover; heterogeneous environments; Casper/FDR.

The growing demand for ubiquitous access of
bandwidth-demanding services and applications is a motivation
for the increase of coverage enabling access to high-quality links
supporting environments with the possibility of mobility and QoS
services. Remote areas exist which pose difficult challenges for
Internet access. New wireless technologies, such as the IEEE
802.16, allow operators to extend coverage to these areas, using
converged WiMAX and WiFi networks. However, this
technology also has its own limitations, regarding the supply of
integrated QoS services and fast mobility support. This paper
discusses a network architecture which is able to support real
time services using 802.16 networks as a backhaul, providing an
integrated QoS approach over the 802.16 network. We introduce
the concept of backup channel used to receive real-time services
during the reservation setup time, avoiding packet losses or
delays in these services. We also present an algorithm for
dynamic management of the backup channel, and performance
results of this algorithm. Finally, we show the efficiency of our
solution for QoS support in these networks.

Current mobile devices are equipped with multi-standard interfaces to fully utilize both the existing and the imminent Public Land Mobile Network infrastructure. This flexibility comes with significant energy consumption overheads at the mobile terminal side and thus, the adopted interface / network selection scheme, a.k.a. Vertical Handover mechanism, should be based on both Quality of Service oriented and energy-efficiency criteria. This paper summarizes the current state of the art on energy-centric vertical handover algorithms, discusses weak aspects of existing approaches and presents a novel context-aware vertical handover framework towards energy-efficiency. Rather than a pure energy-centric vertical handover scheme, this framework is a context-awareness enabler for energy-centric vertical handover decision making.

Vertical handover decision algorithm that is based on user preferences and coupled with Media Independent Handover (MIH) local triggers have not been explored much in the literature. We have developed a comprehensive crosslayer solution, called Vertical Handover Decision (VHOD) approach, which consists of three parts viz. mechanism for collecting and storing user preferences, Vertical Handover Decision (VHOD) algorithm and the MIH Function (MIHF). MIHF triggers the VHOD algorithm which operates on user preferences to issue handover commands to mobility management protocol. VHOD algorithm is an MIH User and therefore needs to subscribe events and configure thresholds for receiving triggers from MIHF. In this regard, we have performed experiments in WLAN to suggest thresholds for Link Going Down trigger. We have also critically evaluated the handover decision process, proposed Justintime interface activation technique, compared our proposed approach with prominent user centric approaches and analyzed our approach from different aspects.

As wireless access technologies grow rapidly, the recent studies have focused on granting mobile users the ability of roaming across different wireless networks in a seamless manner thus offering seamless mobility. The different characteristics of each wireless technology with regards to QoS brought many challenges for provisioning the continuous services (audio/video streaming) in a seamless way. In this paper, we intend to review the existing context-aware methods which offered solutions for service continuity. We looked at the types of context information used in each solution. Through this study, it is clear that context awareness plays a significant role in handover process in order to satisfy users demanding seamless services. Therefore, the goal of this paper is to compare the existing methods grouped as general, IMS based, and WLAN/WiMAX solutions in terms of several criteria, such as interworking architecture, service continuity, and QoS provisioning.

In next generation wireless network the most desirable feature is its ability to move seamlessly over various access network regardless of the network infrastructure is used. The handover between these dissimilar networks can be explored by using vertical handover algorithms. This paper focuses on the vertical handover decision methods and algorithms effectiveness. Most of the algorithms which are based on RSS values provide vertical handover with small delay at a lower rate of throughput. There are such algorithms which provide significant improvements in throughput but at a cost of higher delays. As per the need for the real time applications in next generation wireless networks there is a requirement of developing new optimized algorithms that are able to produce high throughput and minimizing signalling cost and delay.

Vertical handover decision algorithm that is based on user preferences and coupled with Media Independent Handover (MIH) local triggers have not been explored much in the literature. We have developed a comprehensive cross-layer solution, called Vertical Handover Decision (VHOD) approach, which consists of three parts viz. mechanism for collecting and storing user preferences, Vertical Handover Decision (VHOD) algorithm and the MIH Function (MIHF). MIHF triggers the VHOD algorithm which operates on user preferences to issue handover commands to mobility management protocol. VHOD algorithm is an MIH User and therefore needs to subscribe events and configure thresholds for receiving triggers from MIHF. In this regard, we have performed experiments in WLAN to suggest thresholds for Link Going Down trigger. We have also critically evaluated the handover decision process, proposed Just-in-time interface activation technique, compared our proposed approach with prominent user centric appr...

This paper proposes a fair and efficient QoS scheduling scheme for IEEE 802.16 BWA systems that satisfies both throughput and delay guarantee to various real and non-real time applications. The proposed QoS scheduling scheme is compared with an existing QoS scheduling scheme proposed in literature in recent past. Simulation results show that the proposed scheduling scheme can provide a tight QoS guarantee in terms of delay, delay violation rate and throughput for all types of traffic as defined in the WiMAX standard, thereby maintaining the fairness and helps to eliminate starvation of lower priority class services. Bandwidth utilization of the system and fairness index of the resources are also encountered to validate the QoS provided by our proposed scheduling scheme.

The primary focus of this review is tropical-extratropical interactions and especially the issues involved in determining the response of the extratropical atmosphere to tropical forcing associated with sea surface temperature (SST) anomalies. The review encompasses observations, empirical studies, theory and modeling of the extratropical teleconnections with a focus on developments over the Tropical Oceans-Global Atmosphere (TOGA) decade and the current state of understanding. In the tropical atmosphere, anomalous SSTs force anomalies in convection and large-scale overturning with subsidence in the descending branch of the local Hadley circulation. The resulting strong upper tropospheric divergence in the tropics and convergence in the subtropics act as a Rossby wave source. The climatological stationary planetary waves and associated jet streams, especially in the northern hemisphere, can make the total Rossby wave sources somewhat insensitive to the position of the tropical heating that induces them and thus can create preferred teleconnection response patterns, such as the Pacific-North American (PNA) pattern. However, a number of factors influence the dispersion and propagation of Rossby waves through the atmosphere, including zonal asymmetries in the climatological state, transients, and baroclinic and nonlinear effects. Internal midlatitude sources can amplify perturbations. Observations, modeling, and theory have clearly shown how storm tracks change in response to changes in quasi-stationary waves and how these changes generally feedback to maintain or strengthen the dominant perturbations through vorticity and momentum transports. The response of the extratropical atmosphere naturally induces changes in the underlying surface, so that there are changes in extratropical SSTs and changes in land surface hydrology and moisture availability that can feedback and influence the total response. Land surface processes are believed to be especially important in spring and summer. Anomalous SSTs and tropical forcing have tended to be strongest in the northern winter, and teleconnections in the southern hemisphere are weaker and more variable and thus more inclined to be masked by natural variability. Occasional strong forcing in seasons other than winter can produce strong and identifiable signals in the northern hemisphere and, because the noise of natural variability is less, the signal-to-noise ratio can be large. The relative importance of tropical versus extratropical SST forcings has been established through numerical experiments with atmospheric general circulation models (AGCMs). Predictability of anomalous circulation and associated surface temperature and precipitation in the extratropics is somewhat limited by the difficulty of finding a modest signal embedded in the high level of noise from natural variability in the extratropics, and the complexity and variety of the possible feedbacks. Accordingly, ensembles of AGCM runs and time averaging are needed to identify signals and make predictions. Strong anomalous tropical forcing provides opportunities for skillful forecasts, and the accuracy and usefulness of forecasts is expected to improve as the ability to forecast the anomalous SSTs improves, as models improve, and as the information available from the mean and the spread of ensemble forecasts is better utilized.

Abstract. The primary focus of this review is tropical-extratropical interactions and especially the issues involved in determining the response of the extratropical atmosphere to tropical forcing associated with sea surface temperature (SST) anomalies. The review encompasses ...

The MEDIEVAL project aims to leverage today's Internet with the necessary fabric to provide optimized video services in a mobile wireless world. It is expected that video traffic will surpass Peer-to-Peer (P2P) in volume in the coming years, and thus novel mechanisms and techniques need to be provided to better suit its unique requirements. This article describes the key functional elements of the MEDIEVAL architecture, which provides a video-aware networking core coupled with abstracting interfaces which cater to service and access technology specific requirements, aiming to enable efficient video transport and novel video service development.

Terrestrial wireless network technologies such as UMTS, WiMax and WLAN are used to provide network
access for both voice and data services. In big cities the densely populated areas like town centres,
shopping centres and train stations which have coverage of multiple wireless networks, a large number
of mobile users may be connected to the more common UMTS, thereby creating an unbalanced load
across these wireless networks. This high load variation can be balanced by moving mobile users from
heavily loaded networks to least loaded networks which involves execution of vertical handovers.
Seamless vertical handovers across different wireless networks may be achieved using the IEEE 802.21
Media Independent Handover (MIH) specifications.

Mobile WiMAX uses EAP-based authentication and key management for link layer
security. One of the major challenges concerning the performance of mobile WiMAX is seamless
handover. Research shows that a large portion of delay related to handover actually comes from
user authentication and network entry and re-entry.
In general, total delay associated with the handover process can be divided into three categories:
i) link layer handover delay, ii) IP layer handover delay, and iii) security sub-layer handover
delay. We propose a pre-authentication design that can provide seamless and safe connection
when handover takes place.
Our design is based on the least privilege principle; therefore, our approach guarantees
backward/forward secrecy. We conduct research using an ns-2 simulation tool to measure the
performance of our seamless handover. Our approach is validated using automated validation of
Internet Security Protocols and Applications (AVISPA).

Envisioning a future where mobile terminals equipped with one or more network devices are able to roam across wireless or wired networks, in a diverse macro and micro wireless cells environment, requires the development of enhanced methods to control IP-based mobility. These methods should consider traditional terminal mobility (mainly due to user movement) as well as mobility across heterogeneous networks in the presence of semi-static users. For this to become reality, a cross layer interaction is required starting from a potentially large diversity of layer two access technologies up to the common IP layer, allowing the exchange of messages between terminals and network components. Furthermore, traditional host mobility driven concepts need to evolve, and include more stringent mobile operator requirements in context of fully driven network controlled mobility. This paper presents and evaluates a novel framework design, based on the IEEE 802.21 future standard, encompassing network driven as well as host driven mobility. This paper evaluates signalling aspects, algorithm design and performance issues.