International Journals

ABSTRACT
In the context of cloud-enabled 5G radio access networks with network function virtualization capabilities, we focus on the virtual network function placement problem for a multi-tenant cluster of small cells that provide mobile edge computing services. Under an emerging distributed network architecture and hardware infrastructure, we employ cloud-enabled small cells that integrate micro servers for virtualization execution, equipped with additional hardware appliances. We develop an energy-aware placement solution using a robust optimization approach based on service demand uncertainty in order to minimize the power consumption in the system constrained by network service latency requirements and infrastructure terms. Then, we discuss the results of the proposed placement mechanism in 5G scenarios that combine several service flavours and robust protection values. Once the impact of the service flavour and robust protection on the global power consumption of the system is analyzed, numerical results indicate that our proposal successes to efficiently place the virtual network functions that compose the network services in the available hardware infrastructure while fulfilling service constraints.

ABSTRACT
Nowadays, citizens are getting used to new ways of agile communications supporting media-enriched and context-aware information. However, the adoption of these evolved technologies in emergency communications between citizens and public authorities face a series of barrier, including the lack of harmonized and interoperable solutions. Different initiatives worldwide are addressing the need for specifying a stable IP-based next generation emergency communications framework. This paper provides a general overview of the different international approaches with especial focus on the European perspective, where the NG112 architecture has been specified and has now entered the testing and evaluation phase.

ABSTRACT
This paper analyzes current standardization situation of 5G and the role network softwarization plays in order to address the challenges the new generation of mobile networks must face. This paper surveys recent documentation from the main stakeholders to pick out the use cases, scenarios and emerging vertical sectors that will be enabled by 5G technologies, and to identify future high-level service requirements. Driven by those service requirements 5G systems will support diverse radio access technology scenarios, meet end-to-end user experienced requirements and provide capability of flexible network deployment and efficient operations. Then, based on the identified requirements, the paper overviews the main 5G technology trends and design principles to address them. In particular, the paper emphasizes the role played by three main technologies, namely SDN, NFV and MEC, and analyzes the main open issues of these technologies in relation to 5G.

ABSTRACT
5G envisages a hyper-connected society where trillions of diverse entities could communicate with each other anywhere and at any time, some of which will demand extremely challenging performance requirements such as sub-millisecond low latency. Mobile Edge Computing (MEC) concept where application computing resources are deployed at the edge of the mobile network in proximity of an end user is a promising solution to improve quality of online experience. To make MEC more flexible and cost-effective Network Functions Virtualisation (NFV) and Software-Defined Networking (SDN) technologies are widely adopted. It leads to significant CAPEX and OPEX reduction with the help of a joint radio-cloud management and orchestration logic. In this paper we discuss and develop a reference architecture for the orchestration and management of the MEC ecosystem. Along with the lifecycle management flows of MEC services, indicating the interactions among the functional modules inside the orchestrator and with external elements, QoS management with a focus on the channel state information technique is presented.

ABSTRACT
Many years of research have been dedicated toward the definition of sophisticated quality of service (QoS) measurement tools and methods. Nonetheless, the results given to end users by most commonly used online speed measurement tools are still far from being accurate. Among other factors, the reliability of the measurement methods is affected by different static and dynamic constraints of involved network nodes and TCP/IP implementations. The clarification of such uncertainties will help establish the baseline for the definition of any comparable and technically feasible measurement methodology, in terms of measurement periods, number of concurrent connections, and convergence time. This article presents a comprehensive description of the research work and proposes mechanisms, aiming to obtain a full understanding of cross-layer effects during a speed test targeting end users.

ABSTRACT
Current trends in broadband mobile networks are addressed towards the placement of different capabilities at the edge of the mobile network in a centralised way. On one hand, the split of the eNB between baseband processing units and remote radio headers makes it possible to process some of the protocols in centralised premises, likely with virtualised resources. On the other hand, mobile edge computing makes use of processing and storage capabilities close to the air interface in order to deploy optimised services with minimum delay. The confluence of both trends is a hot topic in the definition of future 5G networks. The full centralisation of both technologies in cloud data centres imposes stringent requirements to the fronthaul connections in terms of throughput and latency. Therefore, all those cells with limited network access would not be able to offer these types of services. This paper proposes a solution for these cases, based on the placement of processing and storage capabilities close to the remote units, which is especially well suited for the deployment of clusters of small cells. The proposed cloud-enabled small cells include a highly efficient microserver with a limited set of virtualised resources offered to the cluster of small cells. As a result, a light data centre is created and commonly used for deploying centralised eNB and mobile edge computing functionalities. The paper covers the proposed architecture, with special focus on the integration of both aspects, and possible scenarios of application.

ABSTRACT
This paper presents a novel architecture for optimizing the HTTP-based multimedia delivery in multi-user mobile networks. This proposal combines the usual client-driven dynamic adaptation scheme DASH-3GPP with network-assisted adaptation capabilities, in order to maximize the overall Quality of Experience. The foundation of this combined adaptation scheme is based on two state of the art technologies. On one hand, adaptive HTTP streaming with multi-layer encoding allows efficient media delivery and improves the experienced media quality in highly dynamic channels. Additionally, it enables the possibility to implement network-level adaptations for better coping with multi-user scenarios. On the other hand, mobile edge computing facilitates the deployment of mobile services close to the user. This approach brings new possibilities in modern and future mobile networks, such as close to zero delays and awareness of the radio status. The proposal in this paper introduces a novel element, denoted as Mobile Edge-DASH Adaptation Function, which combines all these advantages to support efficient media delivery in mobile multi-user scenarios. Furthermore, we evaluate the performance enhancements of this content- and user context-aware scheme through simulations of a mobile multimedia scenario.

ABSTRACT
The current financial situation, together with the new market conditions, has led to major changes in the ICT sector over the last few years. Many services that in the past were only offered by operators are now held by third parties through the cloud, which has caused a shift towards new business models at the expense of a more traditional market. Furthermore, these economic changes have conducted to socio-cultural transformations with great impact on the user’s behaviors. In this paper a cloud platform for the measurement and evaluation of the Quality of Experience (QoE) is presented. The platform is based in a model (QoXphere) that ensures the user satisfaction in terms of Quality of Service (QoS) and the provider economic benefits, as demanded in current market situation. In addition, the proposed cloud architecture intends to help in the advance of the work item recently opened in ITU-T to establish an ITU recognition procedure of testing laboratories with competence in ITU-T Recommendations by providing a unified cloud environment in which to validate them.

ABSTRACT
IP Multimedia Subsystem (IMS) is becoming the prevailing candidate for managing future mobile multimedia communications, including critical communications such as public safety, emergency professionals and corporate networks. IMS security and privacy has gained much attention in the few last years. The review of recent IMS security activities stresses the inclusion of intermediate nodes in the media path of secured communications as an open issue. This paper presents an end-to-middle-to-end solution which enables the usage of IMS media plane elements such as recorders, transcoders and novel cross-ciphering functions in a secure way. The proposed solution, which is fully compliant with IMS, includes the network architecture, the signaling plane for session signaling and key management, and the media-plane security characteristics. Experimental results demonstrate that the proposed solution can provide media interoperability (both transcoding and cross-ciphering) with a cost of 17% overhead to a standard IMS call setup in the signaling plane.

ABSTRACT
This paper deals with the resource allocation problem aimed at maximizing users’ perception of quality in wireless channels with time-varying capacity. First of all, we model the ubjective quality-aware scheduling problem in the framework of Markovian decision processes. Then, given that the obtaining of the optimal solution of this model is unachievable, we propose a simple scheduling index rule with closed-form expression by using a methodology based on Whittle approach. Finally, we analyze the performance of the achieved scheduling proposal in several relevant scenarios, concluding that it outperforms the most popular existing resource allocation strategies.

ABSTRACT
In this paper we study how to design a scheduling strategy aimed at minimizing the average holding cost for flows with general size distribution when the feasible transmission rate of each user varies randomly over time. We employ a Whittle-index-based approach in order to achieve an opportunistic and non-anticipating size-aware scheduling index rule proposal. When the flow size distribution belongs to the Decreasing Hazard Rate class, we propose the so-called Attained Service Potential Improvement index rule, which consists in giving priority to the flows with the highest ratio between the current attained service-dependent completion probability and the expected potential improvement of this completion probability. We further analyze the performance of the proposed scheduler, concluding that it outperforms well-known opportunistic disciplines.

ABSTRACT
This paper deals with the analysis of mobile multimedia services, with special focus on current media resolutions for mobile handsets. Since variable network conditions entail variable quality levels, nowadays several applications implement some kind of dynamic service adaptation in order to mitigate these effects. This paper analyzes the service performance from an end-to-end perspective, taking into account the several agents involved in the service provision. From a detailed study, the different possible sources of degradations are identified as well as their impact into the expected quality as perceived by end users. Based on the obtained results, the possible effects of different adaptation capabilities are discussed. The identification of the main source of degradations at the destination endpoint improves the adaptation capabilities and enhances the service performance in terms of perceived quality.

ABSTRACT
The telecommunications sector has experienced significant changes over the past few years. The advent and rise of new applications and services, together with a competitive market, has led to a complex scenario in which quality of service plays a major role. Under this condition, novel QoS regulation and standardization initiatives are required. During the last few years new terms and concepts, such as quality of experience or QoS perceived, have been included in the updated and new QoS-related standards as to better integrate the user's point of view, as opposed to only network performance parameters. The influence of the user's satisfaction on the quality of business has also been given increased attention in the regulation and standardization bodies recently. The result is a loose collection of metrics and models that are not standardized and do not integrate all aspects of quality. Such integration is necessary to assure the successful development of this sector. This paper presents a new and integrated QoS model (QoXphere) that is spherical, adaptive, and multi-layered.

ABSTRACT
Most multimedia applications implement some kind of packet losses analysis mechanism to trigger self–adaptation actions. However, error recovery mechanisms such as ARQ variants avoid packet losses at IP level. Then, there appears an impact into the delay that may indeed result on application–level losses due to samples arriving later than the scheduled playout time. In most cases such degradations are not detected until they are so severe than even losses at IP level appear. We propose a lightweight method that achieves a finer grain estimation. We prove mathematically the capability of modified versions of statistics of delay to predict the error ratio of the wireless link and the load of the wired backhaul. After deducing also simplified heuristics for proposed method, we analyze their estimation capabilities and provide guidance for selecting appropiate parameters.

ABSTRACT
This paper deals with the subjective quality maximization problem when scheduling multimedia traffic flows in a shared channel. In order to quantify such user satisfaction a utility function dependent on flow transfer delay is used. In this context, we formulate the Quality of Experience aware resource allocation optimization problem as a Markov Decision Process. This model is analytically unsolvable in general, and as an approximate solution we develop a simple and tractable index rule based on Gittins approach, originally aimed just at minimizing mean flow delay. As concluded from simulation results, when evaluating subjective quality performance this novel index rule proposal outperforms the most relevant existing scheduling disciplines.

ABSTRACT
A major issue in the application of ad hoc networking to Wireless Networked Robotics is the choice of the routing protocol that performs better in a given scenario. However, far too little attention has been paid to routing issues involving enhanced robotic nodes. In view of the lack of a significant and comprehensive analysis, this research work completes an in-depth performance comparison of mostly well-known ad hoc routing protocols under a wide variety of conditions and applies the obtained results to a case study with three examples of real-world Wireless Networked Robotics scenarios.

ABSTRACT
Scalable video coding allows an efficient provision of video services at different quality levels with different energy demands. In order to deal with the resulting trade-off we analyze the number of video layers that are worth to be received taking into account the energy constraints. On one hand, a single-objective optimization is proposed based on dynamically selecting the number of layers, which is able to minimize the energy consumption with the constraint of a minimal quality threshold to be reached. However, this approach cannot reflect the fact that the same increment of energy consumption may result on different increments of visual quality. Thus, a multi-objective optimization is proposed and a utility function defined in order to weight the energy consumption and the visual quality criteria. Finally, since the optimization solving mechanism is computationally expensive to be implemented in mobile devices, a heuristic algorithm is proposed. This way mobile operators and end users could significally reduce their energy consumption while keeping reasonable quality levels.

ABSTRACT
This paper describes the proposal of a priority flow oriented design of the Ksensor architecture. Ksensor is a multiprocessor traffic capture and analysis system for high speed networks developed at kernel space. While the current architecture permits the capture and analysis of data flows, there are several scenarios where it does not perform adequately to achieve this goal, for example, if a certain type of traffic is more valuable than others. Thus, this work pursues the design that allows Ksensor to provide data flow treatment to a larger extent. This improvement will allow the new architecture to provide more reliability in data flow capture and processing.

ABSTRACT
This paper deals with the problem of scheduling mobile Internet traffic over a single cell wireless downlink data channel. On the one hand, we compare the performance of different size-based or/and channel-aware scheduling disciplines in mean delay terms, concluding that an approach that combines both size- and channel-awareness is the best alternative, which guarantees acceptable uplink overhead due to channel information reports. On the other hand, we study the impact of different scheduling algorithms on user's satisfaction for web browsing service. As concluded, in order to achieve a trade-off between maximizing overall mean subjective quality and reducing uplink signaling overhead due to channel quality reports, a scheduling policy that benefits from opportunistic gains in combination with a size-aware tie-breaking rule gives the best results.

ABSTRACT
This paper deals with the analysis of user perceived visual quality for mobile multimedia services. H.264/AVC is selected for low resolution video encoding, and a mobile UMTS network is considered for the access to services. First, from subjective tests results, the combined impact of different service- and radio network-level parameters is inferred. As a result, different cross-layer adaptation alternatives are proposed to maximize the perceived quality level under different service conditions. Afterwards, the backhaul segment is considered taking into account possible congestion effects after the aggregation of multi-user media stream. The proposed dynamic adaptation process determines the best combination of media bitrates in order to optimise the overall quality, by making use of information related to network performance both at the radio and backhaul segments.

ABSTRACT
The inclusion of multimedia content in different web-based services has increased significantly. Through an extensive subjective testing campaign, we analyse the quality of experience concerning video transmissions associated to these types of services when accessed from mobile devices and mobile Internet connections. Contrary to traditional normalised quality assessment studies, we point out the service context as a key aspect in quality assessments. Specifically, we analyse the impact of the duration of the test material on quality assessments. We find out that tolerance to visual degradations is higher in the specific context of use compared to when using standardised methodologies for quality assessment, which has a significant impact in terms of commercial service acceptability.

ABSTRACT
The aim of this paper is to present video quality prediction models for objective non-intrusive, prediction of H.264 encoded video for all content types combining parameters both in the physical and application layer over Universal Mobile Telecommunication Systems (UMTS) networks. In order to characterize the Quality of Service (QoS) level, a learning model based on Adaptive Neural Fuzzy Inference System (ANFIS) and a second model based on non-linear regression analysis is proposed to predict the video quality in terms of the Mean Opinion Score (MOS). The objective of the paper is two-fold. First, to find the impact of QoS parameters on end-to-end video quality for H.264 encoded video. Second, to develop learning models based on ANFIS and non-linear regression analysis to predict video quality over UMTS networks by considering the impact of radio link loss models. The loss models considered are 2-state Markov models. Both the models are trained with a combination of physical and application layer parameters and validated with unseen dataset. Preliminary results show that good prediction accuracy was obtained from both the models. The work should help in the development of a reference-free video prediction model and QoS control methods for video over UMTS networks.

ABSTRACT
The growth of emerging multimedia applications with different quality requirements has made the objective network QoS (NQoS) to be commonly considered as an inadequate metric for quality assessment in telecommunication services, being the quality of experience (QoE) concept the most predominant alternative. However, most QoE-related research studies are service-specific, not easily expandable to other multimedia services and unsuitable for tuning up network management procedures. Instead, we propose an integrated QoE management model and a calculus process that estimates final user-satisfaction over multi-service scenarios and identifies those elements that have a greater impact on users' QoE. In order to evaluate this impact, new VoIP and video perception assessment methods were developed, while state-of-the-art methods were used for web and online game services. The effectiveness of the model is demonstrated by applying a stepwise multiple linear regression method to identify both subjective and objective bottlenecks in the network.

ABSTRACT
Quality of service has become one of the most important factors among Internet service providers. The implementation of appropriate QoS policies is essential in order to maintain customer loyalty and fulfill regulators' requirements. ITU-T recommendation E.802 provides a framework for the identification of QoS criteria relevant to users and ISPs. This Recommendation also provides guidelines to derive measurable QoS parameters from identified criteria. This article presents a QoS management model and implementation methodology for ISPs. We ground our investigation on the E.802 framework, which ISPs may face when implementing ITU-T Recommendation G.1000. The proposed methodology is meaningful for users, vendors, and network operators. Furthermore, its conformance with the ITU-T standard makes it suitable and deployment-ready for both regulators and providers.

ABSTRACT
Most of the currently available adaptation solutions of VoIP over UMTS are based on the modification of service parameters as the only available reaction against any detected service degradation. On the contrary, in this paper we propose a combined approach where service-level adaptation is considered first and, provided that no suitable parameter combination is capable of providing enough QoE, a change of network state will be suggested. In order to do so we analyze the performance of the end-to-end (e2e) performance metrics in this convergent scenario, the root causes of possible degradations and, finally, the combined effects of the different network segments and their impact on the user perceived QoE. We show the map of best performing VoIP configurations for every state of the network segments. Furthermore, considering each of these configurations, we analyze the acceptability of the service or the convenience of trying to modify the network state. Finally, a lightweight implementation based on simple network state estimation and decision heuristics is proposed and validated in terms of accuracy and responsiveness.

ABSTRACT
IMS entails novel business opportunities for pioneering and emerging multimedia services, such as IPTV and VoIP video call applications. However, this strong commercial interest on this promising convergent IMS environment is balanced by the lack of efficient user/customer-centric network management mechanisms. ADAMANTIUM proposes an IMS-compatible Multimedia Content Management System (MCMS) focused on performing dynamic cross layer adaptations for ptimization of the user experience in terms of perceptual quality for media services. This multimodal management system will be applied in an integrated and coherent way along all the network layers and delivery-chain nodes based on a user/customer-centric approach rather than a typical engineering one.

ABSTRACT
Simulation models have been developed in order to foresee characteristics of networks, systems or protocols when carrying out tests in laboratories is very expensive or even impossible. This paper presents a simulation model of a multiprocessor network traffic analysis system. The model, which is based on closed networks of queues, evaluates the efficiency of the system depending on the hardware/software platform features. Therefore, this model is able to estimate performance early in the design and development stages simulating a multiprocessor architecture in charge of analysing network traffic. The goodness of the model will be checked by comparing analytical results with practical ones obtained in laboratory using a traffic analysis system that runs on a multiprocessor platform.