• Jointly optimizes region partitioning and region-specific power pool design. • Proposes a dual-agent DRL framework for cooperative region and power decisions. • Reduces action space complexity using modular base-station agents under CTDE. • Demonstrates superior energy efficiency and SIC success compared to fixed or gap-based baselines and outperforms single-agent in convergence. Achieving energy-efficient transmission with high decoding reliability is a fundamental challenge for massive machine-type communication (mMTC) using grant-free Non-Orthogonal Multiple Access (NOMA), due to dense device activity, sporadic traffic, and strong uplink interference. This paper introduces a Centralized Dual-Agent Deep Reinforcement Learning (CDA-DRL) framework that jointly optimizes region partitioning and transmit power pool design in uplink grant-free NOMA. Two cooperative agents at the base station independently learn the number of spatial regions and the number of power levels, respectively, using recurrent Deep Q-Networks under a centralized training and decentralized execution paradigm. This factorized architecture reduces the action-space complexity and enables scalable learning. Simulation results demonstrate that CDA-DRL achieves more stable training, higher Successive Interference Cancellation (SIC) decoding success, and significantly improved energy efficiency, outperforming geometric gap–based baselines by up to 114% and fixed-power schemes by 33%.

The increasing number of connected and autonomous vehicles generates an even greater demand for efficient content delivery in vehicular networks. Estimating the popularity of content is an important task to proactively cache and distribute content throughout the networks to add value to users' experiences and reduce network congestion. This paper presents a novel approach for predicting popular content on vehicular networks based on a Federated Learning-Adversarial Autoencoder model and anonymised data. Unlike prior works that relied on users' raw features, our model protects user privacy through data anonymisation. This allows us to learn from the hidden patterns of content popularity and deliver popular content without compromising user privacy. Experiments showed that our approach exceeded traditional collaborative filtering and deep learning methods in terms of accuracy and robustness, even with sparse data.

This paper presents a novel approach to resource allocation in Cell-Free Massive MIMO networks, with a particular focus on supporting Ultra-Reliable Low-Latency Communications (URLLC). Traditional solutions typically rely on successive refinements of an initial allocation, which leads to high computational complexity and limits their practicality in real-time environments, especially when addressing the heterogeneous requirements of different user equipment types. In contrast, the proposed approach introduces a holistic algorithm that computes the optimal resource allocation for both URLLC and Non-URLLC users without requiring successive refinements, ensuring a globally optimized solution is obtained directly. This optimization significantly enhances computational efficiency while preserving high spectral performance across the network. The proposed algorithms achieve better results when compared to the State-of-the-Art methods regarding average spectral efficiency and the 90%-likely spectral efficiency while optimizing both metrics simultaneously. Moreover, the computational complexity of the proposed algorithms is significantly lower than that found in related works, especially in scenarios with 5 pilots, where state-of-the-art algorithms are more than 35 times slower. This reduction in execution time highlights the potential of our models for real-time applications in dense network scenarios.

Service Function Chains allow the dynamic generation of basic virtual network services in order to build more complex services. They constitute the basis of the flexibility support for 5G and Beyond 5G networks. In order to totally exploit their benefits, the Service Function Chains should adapt to specific user requirements and current network status. The existing mechanisms to compose and embed Service Function Chains mostly disregard energy metrics to guide their decisions, thus resulting in a lack of energy optimisation by network operators. This paper presents a revision of existing Service Function Chain composition and embedding approaches and a discussion of current and future research directions, focused on energy optimisation for adaptive Service Function Chains. Furthermore, an architecture to empower the green orchestration of adaptive Service Function Chains is also drafted.

The widespread use of Machine Type Communication (MTC) has sparked a surge in Machine to Machine traffic, creating a need for efficient wireless network management strategies. The conventional Random Access approach struggles to accommodate the substantial influx of devices that characterize MTC deployment, leading to congestion, delays, and resource wastage. To address these challenges, this study introduces Dynamic Switching Access (DSA), a novel multiple access technique that intelligently alternates between Grant Free and Grant Based protocols based on device intensity. By dynamically adjusting thresholds, DSA capitalizes on the strengths of both protocols, effectively enhancing overall system performance even in scenarios with fluctuating traffic loads. Simulation results conclusively demonstrate that the proposed DSA approach outperforms individual protocols in various multiple access scenarios.

5G networks have strict constraints regarding the services in terms of latency, reliability, and availability, which pose additional challenges to the traditional orchestration solutions, and 6G networks will increment the number of slices and services deployed over different technological domains, adding more difficulties for the orchestrator. Distributed and automated solutions will be essential for this context. This article identifies the main challenges in 5G/6G orchestration and then describes the utility of Artificial Intelligence-driven solutions, outlining an orchestrator architecture for 5G networks. The architecture is then explored as an orchestration solution for two ongoing research projects focused on the deployment of critical services over 5G networks.

Privacy regulations press organisations to handle personal data with reinforced caution. Moreover, organisations are dealing with increasing amounts of Personally Identifiable Information in their systems. Thus, there is a high demand not only for privacy-preserving data processing mechanisms but also privacy-enhancing services. As such, we propose the Personal Data Analyser, a tool that increases privacy assurances and minimises privacy risks through automated privacy-preserving data monitoring and privacy risk assessment mechanisms. Automated data monitoring is achieved with a hybrid mechanism that employs Regular Expressions, Natural Language Processing tools, and machine learning models such as Multilayer Perceptron and Random Forests. Our privacy risk assessment mechanism is based on custom-built crisp and fuzzy models, that consider information such as data processor reputation, data sensitiveness and other inputs in order to assess privacy risk associated with data transactions. Our work is integrated and validated under real use cases of the PoSeID-on platform and warns users whenever potential privacy risks are detected. Validation under PoSeID-on’s pilots and its users proved beneficial not only to assess our solution but also to raise users’ awareness of their data. The results of this work show that our solution is an effective Privacy Enhancing Technology that increases privacy assurances between organisations and their users.

Fog computing emerged to ease the load of resource-constrained devices on the Internet. It provides services and computational devices closer to the users to reduce latency and improve quality of service. For this paradigm to be used in practice, certain optimization tasks need to be solved: to allocate the resources that are available to the users and to perform service placement and routing on the communications executed by them. In this paper, we develop a framework that allows users to offload services and perform communications in a Fog environment. For this, we propose a Mixed Integer Linear Programming (MILP) formulation and a heuristic to map Virtual Networks (VNs) into the substrate network, maximizing fairness of energy and bandwidth usage on the system. Moreover, we propose a MILP formulation and a heuristic to route and offload services of an application in each VN, minimizing energy and latency. We extend both heuristics to be used in dynamic settings with increasing number of users and applications and consider a reconfiguration approach when nodes or links fail in the substrate network. To evaluate the proposed approaches, we use the YAFS simulator and several instances of VNs and services with both randomly generated values and referenced parameters. We observed that the heuristics are able to obtain results close to the optimal value in most settings.

The advances made in sustainable energy technology to power small Internet of Things (IoT) devices have raised the challenge of how to prolong the energy neutral operation (ENO), in which no node depletes its battery and all nodes prevent batteries from overcharging. Extending the operational time of IoT networks through environmental friendly sources (e.g.,solar, thermal, and vibration) is the first stage toward energy sustainable communications. However, it is still a challenge to harvest energy from sustainable sources and dynamic control consumption to avoid over- or underutilization. In light of this, optimization approaches should be proposed to achieve and maintain ENO as long as possible. This article sets out an optimization model and a distributed heuristic that is able to achieve and prolong ENO in IoT networks, by supporting periodic and event-based traffic data. In addition, the proposed solutions achieve ENO by controlling the resulting traffic and the transmissions, including the use of data aggregation. The experimental results show the benefits of the distributed heuristic in terms of time in ENO and the amount of event-traffic delivered to the sink node.

Mission Critical Services (MCS) are associated with public safety networks and their support has been progressively introduced in LTE/5G standards. MCS are composed by distinct functions that are required for voice and critical data communications, along with strict security requirements. Service Function Chaining (SFC) allows the delivery of end-to-end services and considers the order of flows (i.e. functions that must be applied before others) and the components on which such functions can be performed (i.e. at cloud or edge nodes). This paper proposes the design of SFC policies to chain Service Functions of MCS, considering the roles of vehicles in wildfire combating scenarios. The evaluated SFC policies consider security functions at edge nodes with distinct computational platforms. The achieved results demonstrate that the SFC policies need to be carefully designed to reduce disruption of services in MCS scenarios.

Assuring an efficient Quality of Service (QoS) for heterogeneous Internet of Things services is a challenge, mainly due to spectrum scarcity and bandwidth limitations on the radio access network. To solve these problems, efficient management of airtime per station (STA) is necessary. In this work, we propose a scheduler to perform dynamic network slicing in IEEE 802.11ah Networks. The proposed scheduler is based on virtualization technologies to assure QoS restrictions per slice and can be deployed in the Access Point (AP) or in a virtual machine connected to the AP. Network metrics are used to verify QoS violations per slice over time. Once a QoS restriction is detected, the scheduler performs a reallocation of resources re-configuring the Restricted Access Windows parameters that compose a slice, adjusting airtime per STA. To evaluate the proposed scheduler, we consider a dynamic policy. Simulation results in a smart city scenario show that the dynamic policy is able to scale the network and satisfies QoS slice requirements.

With the increase of small devices with networking capabilities, Fog Computing emerged as a paradigm to improve Quality of Service. Yet, since these devices are resource constrained, there is a need to offload computational services and to maintain connectivity while moving. In this work, we aim to improve users experience by creating a new path after mobility occurs and the connection to their resources cannot be used anymore. We propose a MILP formulation and a heuristic to minimize energy consumption and latency to obtain a tradeoff solution between these objectives. These approaches find a single path composed by migration of resources to a new device and data communication path to that device. We compare both approaches, formulation and heuristic, and a baseline first-fit approach on randomly generated topologies, resources and users. The results show that the heuristic obtains solutions that are closer to the optimal, while rejecting less users and using the same number of hops than the baseline.

Due to the large increase of Internet of Things (IoT) devices in the last years, the cloud has been proved unsuitable to deal with the high demand of requests generated by them. To deal with this, fog computing was proposed in order to provide closer computing services in a distributed manner, acting as a middle layer between IoT devices and the cloud. However, these devices have low energy and low computational power. Therefore, strategies to distribute requested services, bundled in a set of applications, are of particular interest. Furthermore, these applications have deadlines that may be short, which have to be met. Hence, models and algorithms are needed to place the requested services in order to meet the deadlines while using the fog as distributed as possible. In this paper, we present a Mixed Integer Linear Programming (MILP) formulation with two main objectives: maximize the fog usage and maximize the fairness throughout the system (fog and cloud). We also propose an heuristic that obtains approximate solutions as fast as possible. We compare both approaches using a set of randomly generated applications composed by different deadlines and services.

Internet of Things (IoT) protocols provide the fundamental mechanisms to collect data from low power devices and lossy networks. IoT protocols collect data blocks from the devices in messages that have one header and a single payload, regardless the size of the payload. This paper presents a solution to collect small size data blocks from low power devices in an efficient way, carrying these data blocks in the payload of a single message. Current solutions do not offer manners to gather many small blocks of data and reduce the overhead of the communication. The proposed solution is a light-weight layer designed to operate with the standard IoT protocol stack aiming to reduce the energy consumption of the energy constrained devices without lowering the data accuracy. The proposed solution was developed in Contiki devices and the measurements conducted on a testbed showed up to 14% energy savings.

Recently, Network Slicing in Radio Access Technologies (RATs) has been proposed as an approach to divide the wireless network infrastructure into isolated logical slices which are defined following their requirements and features in a service-driven way. To the best of our knowledge, the application of Network Slicing has not been explored in IEEE 802.11ah Networks. In this work, we propose a Virtual Network Slicing Broker (VNSB), a Virtual Network Function (VNF) instantiated inside a Software Defined Network (SDN) controller which communicates with an IEEE 802.11ah network Access Point (AP) via a southbound Application Program Interface (API). Based on information obtained by the northbound API, the slicing broker gets the information contained in the slicing templates, which describes the services features and respective Quality of Service (QoS) restrictions. With these data, the slicing broker makes logical slices in the context of the Restricted Access Windows (RAW) which are periodically sent by the AP to the stations (STA) via the Raw Parameter Set (RPS). Since there is no hardware with the IEEE 802.11ah standard available on the market, we validate the proposed solution through extensive simulations in a typical smart city scenario. Results showed the broker capacity to build and manage logical slices per service, respecting the QoS restrictions of each offered service. Moreover, the proposed slicing broker makes use of available resources of neighbor slices reducing delay, packet loss, and efficiently maximizing throughput per slice.

Fog computing provides a low latency access to resources at the edge of the network for resource-constrained devices. The high mobility of some of these devices, such as vehicles, brings great challenges related to resource allocation and management. In order to improve the management of computing resources utilized by mobile users connected to the Fog infrastructure, this paper proposes a virtual machine placement and migration decision model based on mobility prediction. Simulations have shown that moving the virtual machine to a Fog node ahead of the user's route using the proposed approach can decrease by almost 50% the number of migrations needed by the user. The Fog architecture provides an average latency of about 15 milliseconds for the users' applications and the proposed approach presents a lower latency compared to a greedy approach for the VM placement problem.

With the recent emergence of energy-harvesting technologies in wireless devices, new challenges have to be addressed by Machine-to-Machine (M2M) communication protocols. The Neutral Operation problem is a relevant problem that seeks to maintain the energy reserve of a node in a level that minimizes energy depletion and maximizes the usage of the harvested-energy. However, neutral operation in a multihop network is a more complex issue, since the nodes lack full knowledge of the network and the nodes have diverse harvesting and consumption profiles. A simplification of the Neutral Operation problem is proposed, named Neutral Operation of the Minimum Energy Node, in which the node with the lowest amount of energy determines the operation of the whole network. This paper proposes a battery-aware solution, called Routing and Aggregation for Minimum Energy (RAME), that performs data-aggregation on the traffic load according to the minimum energy reserve on the path. As part the proposed solution, a kinetic battery model has been developed to provide non-linear battery level estimation. Besides, the Routing Protocol for Low-Power and Lossy Networks (RPL) was enhanced to use the kinetic battery estimation as metric for parent node selection and to find periodically the minimum energy reserve on the available paths. The performance evaluation of the proposed mechanism using Contiki shows the benefits of RAME in comparison to the M2M standard protocols.

Cloud computing is the latest trend in business for providing software, platforms and services over the Internet. However, a widespread adoption of this paradigm has been hampered by the lack of security mechanisms. In view of this, the aim of this work is to propose a new approach for detecting anomalies in cloud network traffic. The anomaly detection mechanism works on the basis of a Support Vector Machine (SVM). The key requirement for improving the accuracy of the SVM model, in the context of cloud, is to reduce the total amount of data. In light of this, we put forward the Poisson Moving Average predictor which is the core of the feature extraction approach and is able to handle the vast amount of information generated over time. In addition, two case studies are employed to validate the effectiveness of the mechanism on the basis of real datasets. Compared with other approaches, our solution exhibits the best performance in terms of detection and false alarm rates.

This paper investigates user provided networks. Such networks have become important research in the field of informatics engineering due to the recent popularity of smart phones. User provided networks are independent from traditional Internet service providers. Communication and information exchange between users occurs opportunistically, i.e., when the smart phones are close enough to exchange information. Most user provided networks are based on the radio standard IEEE 802.11, popularly known as `wi-fi'. However, some networks are based on other low range radio standards, such as Bluetooth and IEEE 802.15.4. User provided networks are important to the society when the traditional Internet service providers become unavailable. For example, this may occur in terrorist attacks, earthquakes, or even cyber attacks. In these emergency situations, when users have a greater interest in common, an efficient system for non-presencial information exchange is necessary. Such networks are also interesting in a social context, when users must be incentivized to share their resources (storage capacity, wireless connectivity and battery) to enable the exchange of information. This paper addresses both situations: i) networks whose users have a common interest and ii) networks whose users need to be encouraged to share resources. Basically, the contributions of this paper can be summarized as the Delay Tolerant Reinforcement-Based routing solution and the Messages on oFfer incentive mechanism. The first is a routing solution for user provided networks when the users have a prior interest in common. The second is an incentive mechanism to encourage users to exchange information. Both solutions showed excellent results in the simulation environment.

Network management includes several operations that aim to maximize Fault, Configuration, Account, Performance and Security (FCAPS) goals. Performance improvement often relies on multiple criteria, leading to NP-Hard optimisation problems. Very often, optimization mechanisms are narrowed to a specific scenario or present deployment issues due to their associated complexity. Others, despite reducing complexity, have accuracy issues that lead to the selection of non-optimal solutions. MeTHODICAL is an accurate optimisation technique for path selection in multihoming scenarios that enhances network management FCAPS goals by being flexible enough to operate on distinct scenarios, supporting different applications and services and with reduced deployment complexity.

In this paper we address the challenge of creating an electronic ticketing system for transportation systems that can partially or completely run on the cloud. This challenge is defined within the scope of an industrial project. The resulting system should be able to reach a large spectrum of customers and should provide two key advantages: lower operational costs, especially for small clients without IT departments, and faster execution of queries for monthly or other sorts of analysis, using the elasticity of cloud-based resources. To fulfill the goals of the project, we propose very standard technologies and procedures: a three-tiered architecture; a separation of the online and analysis databases; and an Enterprise Service Bus to get the input from very diverse hardware and software stacks. In this paper we discuss several options regarding the location of these facilities on the cloud and we also evaluate the costs involved. While this work already defines many features of the system, it must be considered as preliminary, as some open details remain for future work.

Machine-to-Machine technology supports several application scenarios, such as smart metering, automotive, healthcare and city monitoring. Smart metering applications have attracted the interest of companies and governments since these applications bring many benefits (e.g. costs reduction and increased reliability) for production, monitoring and distribution of utilities, such as gas, water and electricity. Multi-hop wireless communication is a cost-effective technology for smart metering applications because it extends the wireless range and enables fast deployment. Smart metering data communicated via wireless multi-hop approaches needs mechanisms that makes the communication less vulnerable to security threats and saves the device resources. Data encryption and data aggregation mechanisms emerge as potential solutions to fulfill these requirements. However, the simultaneous execution of data encryption and data aggregation mechanisms is not a trivial task. This is because the data encryption prevents the data aggregation mechanism to summarize the data along the path. Another challenge is to manage both mechanisms according to the concurrent Machine-to-Machine (M2M) applications interests. In this context, we present sMeter, which is a framework that deals with multiple applications interests, avoiding interest conflicts of concurrent users and supporting the management of data aggregation and data encryption. sMeter is implemented using low-cost hardware in an indoor environment. The communication is performed via a wireless multi-hop technology, and the performance of this communication is evaluated in terms of delay, data reception ratio and received signal strength indication.

Quality of Resilience (QoR) is natively connected to cloud computing to enable high-availability of services and secure access to information. QoR, in such dynamic contexts, cannot simply rely on reactive protection models, such as the primary-backup model supported by the Stream Control Transport Protocol (SCTP). Indeed, proactive mechanisms are required to enable an optimal QoR. In this paper we propose the use of multiple criteria that assess the performance of services operating in the cloud to trigger proactive resilient mechanisms. Such criteria, considering the maximization of benefits and decrease of costs, are combined through Multiple Attribute Decision Mechanisms (MADM) to optimize quality of resilience, going beyond mechanisms relying simply on network criteria. In this context, TOPSIS and MeTH are implemented to enhance data transfer services. Evaluation results, from the tests performed in the cloud environment of a Telecom Operator, demonstrate that MeTH is able to enhance high volume data transfers in comparison to TOPSIS and also to improve resilience support of SCTP, in the presence of different kinds of failures, network conditions and server loads.

Online video transmissions over wireless networks are rising in popularity and have already become part of our daily life. In the meantime, it is necessary to address a number of challenges ranging from the scarce resources, time-varying, and high error rates, to the fluctuating bandwidth, unveiling the need for an adaptive mechanism to ensure a good video transmission. Adaptive Forward Error Correction (FEC) techniques with Quality of Experience (QoE) assurance are appropriate to deliver QoE-aware video data to wireless users in dynamic and high error rates networks. This paper proposes an adaptive Video-aware FEC and Fuzzy Logic-based mechanism to shield realtime video transmissions against packet loss in wireless networks, improving both user experience and the usage of resources. The benefits and drawbacks of the proposed mechanism compared with exiting work are demonstrated through simulations and assessed with QoE metrics.

Video transmission over wireless networks has shown a great increase in recent years and it is becoming part of our daily life. Meanwhile, several difficulties can impair the success of the transmission, such as limited network resources, high error rates and fluctuating signal strength that may lead to variable bandwidth. Therefore there is the need for adaptive mechanisms that can provide a good video transmission. Adaptive Forward Error Correction (FEC) techniques which assure Quality of Experience (QoE) are a convenient means of delivering video data to wireless users in dynamic and error prone networks, while taking into account the content of the transmitted data. This paper proposes an adaptive content-aware and Random Neural Network (RNN) based mechanism to provide protection of real-time video streams against packet loss in wireless networks, improving user experience and optimising network resources. The benefits of the proposed mechanism are demonstrated through simulations and assessed with QoE metrics.

Infrastructure-less wireless multi-hop networks have long been proposed for natural disaster and warfare scenarios. However, the current demand of such networks has been towards social networking, gaming and ultimately, ubiquitous computing. In fact, the increasing number of users that own wireless capable devices is taking these networks to an entirely different scale. Existing routing protocols do not scale and do not consider the context wherein services operate. By presenting an alternative routing protocol that appropriately handles mobility of users among different contexts, large-scale clustered wireless networks are designed, using an efficient gateway selection with load-balancing capabilities. This protocol is based on the PhD work that defines a routing approach which uses a virtual hierarchy of clusters to explore the contextual-proximity of nodes, while reducing the total overhead of routing traffic even when compared with other cluster-based approaches. Moreover, this protocol also takes advantage of a Kernel-based link quality estimator, also considered during the course of the PhD thesis, which is capable of predicting gateway link disconnections, increasing the total amount of delivered data. The obtained results reveal that this routing scheme outperforms existing routing protocols regardless of the mobility pattern being used, being consistently lighter in overhead and delivering up to 50% more data traffic. These results motivate a new era of large-scale wireless multi-hop networks suitable for hand-held devices exchanging data amongst themselves.

Wireless Mesh Networks (WMNs) are increasingly deployed to enable thousands of users to share, create, and access live video streaming with different characteristics and content, such as video surveillance and football matches. In this context, there is a need for new mechanisms for assessing the quality level of videos because operators are seeking to control their delivery process and optimize their network resources, while increasing the user’s satisfaction. However, the development of in-service and non-intrusive Quality of Experience assessment schemes for real-time Internet videos with different complexity and motion levels, Group of Picture lengths, and characteristics, remains a significant challenge. To address this issue, this article proposes a non-intrusive parametric real-time video quality estimator, called MultiQoE that correlates wireless networks’ impairments, videos’ characteristics, and users’ perception into a predicted Mean Opinion Score. An instance of MultiQoE was implemented in WMNs and performance evaluation results demonstrate the efficiency and accuracy of MultiQoE in predicting the user’s perception of live video streaming services when compared to subjective, objective, and well-known parametric solutions.

This paper introduces EVA, a mechanism that enhances VoIP applications by optimizing path selection, taking into consideration multihoming, traffic performance and application performance criteria. These criteria are hierarchically organized according to their type, which can be classified as benefits or costs. EVA solves the NP-hard path selection problem through a MADM technique that employs a new distance function and a stability factor to select paths with optimal quality, while assuring the highest quality of experience during the VoIP call. The EVA solution mitigates unstable scoring, commonly found in MADM techniques, while keeping the same complexity O(m·n). EVA is evaluated analytically using data from a wireless testbed with multihomed hosts. Results demonstrate that EVA selects paths with high quality of experience levels and it is able to maintain the quality levels throughout the sessions. Moreover, when compared to similar techniques, the proposed approach demonstrates higher flexibility and adaptability to heterogeneous scenarios with different characteristics.

Wireless Mesh Networks (WMNs) provide ubiquitous Internet access for mobile users by integrating wired and wireless networks and are a valuable component of new generation communication systems. As gateways towards wired networks are potential bottlenecks, load balancing between multiple gateways plays a central role in the performance of the WMNs. This is especially important for demanding interactive applications such as Voice over IP in the multi-hop WMNs environment. In this paper a Routing Algorithm for Inter-cluster Load Balancing (RAILoB) in WMNs is set out to improve traffic performance. A simulation study has been carried out to assess the performance of RAILoB with a different number of gateways. The results showed that when RAILoB is used as a load balancing mechanism, the traffic performance in multiple gateway WMNs is improved, while keeping the overhead within acceptable bounds.

Video traffic has been growing significantly and it is expected to be a large share of the future Internet traffic, within an increasingly mobile environment with scarce resources. In this context, new challenges arise, and energy-efficiency is becoming a key factor for the successful deployment of mobile networks. The development and validation of mechanisms for energy-efficient video transmission require the measurement of the energy consumption needed for video transmission, considering also the end-user Quality of Experience. This issue is of utmost importance, as users will tailor their application and network usage behaviors based on the perceived quality of the services and on the capabilities of their devices. In this work, an integrated empirical methodology to assess the video transmission energy consumption and quality is proposed. The developed methodology was validated on two distinct testbeds, one with IEEE 802.11 and the other with IEEE 802.16e. Results showed that the proposed methodology enables an accurate assessment of energy consumption with different technologies, while measuring the end-user Quality of Experience. Another contribution of the proposed methodology is the capability to gather data to support the creation and validation of realistic simulation models.

Nowadays, the existing myriad of wireless capable devices has led to the development of numerous multi-hop routing protocols. From proactive to reactive and even hybrid routing approaches, these protocols have motivated the definition of autonomous and ubiquitous ad-hoc networks. Such networks have been idealized not only for disaster and rural scenarios, but also for an increasingly demanding social context in urban areas. However, being able to handle these networks in a large scale, still remains a challenge. Even though several routing solutions resort to clustering and hierarchies in order to limit routing information, the existing nodes' interactions are typically disregarded and mobility amongst different clusters still raises routing issues. In this work the scalability of three routing protocols will be analysed, by defining different size scenarios, while also assessing their routing performance with a mobile node moving between different clusters. Theoretical and simulation based results are presented, using twenty different possible transitions through the existing clusters. This evaluation provides an important contribution, revealing that hierarchical routing organizations' scalability is closer to what is theoretically expected, contrary to other routing solutions. Moreover, regarding the best routing performance which takes into account communities, these results motivate the further utilization of such schemes for future large scale ubiquitous networks.

Wireless Mesh Networks (WMNs) are being called upon to improve their management policies to support a wide range of multimedia applications. As gateways towards wired networks are potential bottlenecks, cluster load balancing routing methods between multiple gateways play a central role in the routing management of the WMNs. This is especially important for demanding interactive applications, for instance triple play services which include traditional applications such as data applications, voice, and video over IP. However, the current performance assessment of these methods does not take into consideration triple play services in their traffic model and this paper seeks to fill this gap. This entails providing a detailed description of each method and carrying out a comparative evaluation by simulating a traffic model for triple play services. This performance assessment compares these cluster load balancing methods by assessing the traditional traffic performance parameters, while varying the traffic load which is the main variable factor that affects the load balancing methods. The results support that the cluster load balancing routing methods as well as the traffic load have a significant impact on each application performance when the applications are evaluated separately and moreover, they still have impact on the triple play services but it is lesser significant than when a single application is evaluated. Furthermore, the most agile and flexible method results in more scalable triple play service.

Nowadays, the existing myriad of wireless capable devices has led to the development of numerous multi-hop routing protocols. In particular, due to the scale of these networks, routing protocols with well defined hierarchies have been proposed. By defining different size scenarios with twenty different possible transitions in hierarchies for 2, 3 and 4 clusters, the impact of using such mechanism is evaluated. Simulation based results are presented for 2 different routing protocols showing that a Deferred Routing approach is able to successfully handle hierarchical transitions, delivering up to 4.5 times more data traffic than the remaining protocols, while maintaining a lower overhead. These results motivate the further utilization of such scheme for future large scale wireless networks.

Wireless Multimedia Sensor Networks (WMSNs) play an important role in pervasive and ubiquitous systems. The multimedia content in such networks has the potential of enhancing the level of information collected, enlarging the range of coverage, and enabling multi-view support. For WMSN applications, the multi-tier network architecture has proven to be more beneficial than a single-tier in terms of energy-efficiency, scalability, functionality and reliability. In this context, a multimedia intrusion detection application appears as a promising application of multi-tier WMSNs, where the lower tier can detect the intruder using scalar sensors, and the higher tier camera nodes will be woken up to send real time video sequences from the detected area. The transmission of multimedia content requires a certain quality level from the user perspective, while energy consumption and network overhead should be minimized. Among the existing mechanisms for improving video transmissions, Forward Error Correction (FEC) can be regarded as a suitable solution to improve video quality level from the user point-of-view. In this work, we propose a Quality of Experience (QoE)-aware FEC mechanism for WMSNs, which creates redundant packets based on impact of the frame on the user experience. According to the simulation results, our proposed mechanism achieved similar video quality level compared with standard FEC, while reducing the transmission of redundant packets, which will bring many benefits in a resource-constrained system.

In recent years, the ubiquity of multimedia services along with the proliferation of mobile devices and the demand for new audio and video applications are changing the lifestyle of users.The multimedia era is allowing users to create, distribute, and access content in ubiquitous way and cost-effectively, while providers explore new ways to increase their revenues.The efficient delivery of real-time multimedia services over emerging diverse and heterogeneous systems is a challenging research goal.The interoperability of applications, transport and network protocols as well as the demand for improved Quality of Experience (QoE) create new challenges and opportunities for further research on novel communication protocols, architectures, and methods to efficiently support current and future multimedia networking systems.In 2010, the Third International Future Multimedia Networking (FMN 2010) workshop was organized in Kraków, Poland and achieved a success attracting numerous submissions from various countries.FMN 2010 produced a high quality peer reviewed technical programme with an acceptance rate at around 24% and addressed important aspects of future multimedia systems with a focus on QoE.Authors of selected papers from FMN 2010 were invited to submit extended versions of their papers in order to be considered for inclusion in this Special issue on Future Multimedia.

Mobile and multi-access devices have become commonplace today. In this context, nodes have multiple interfaces that can form the foundation for the always best connected paradigm. Mobile IPv6, the staple mobility management technology for the Internet, enables nodes to roam between different networks while minimising session disruption due to handovers. However, in standard MIPv6, a mobile node can register only a single IP address as its Care-of-Address (CoA), therefore the multiplicity of network interfaces may be managed suboptimally while simultaneous multi-access is not possible. Recently, MIPv6 has been extended with a much-anticipated feature, namely Multiple Care-of Address (MCoA) registration. MCoA allows a MIPv6 node to register all active addresses configured on the respective interfaces and then use them at will, possibly in an alternating fashion as well as simultaneously. MCoA is anticipated to improve the performance of multimedia applications, yet this is still to be quantified. This paper provides a first answer to this question. In particular, we employ simulation to evaluate the benefits for multimedia applications, such as VoIP and video, from the use of MCoA. We compare the MCoA results with those obtained when MIPv6 with single address registration is used based on objective multimedia evaluation metrics, such as PESQ. In addition we examine the tradeoffs between application benefits and signaling costs for the network.

Resilience, load balancing and ubiquitous support can be improved by multihoming configurations that explore the plurality of wireless technologies available nowadays. Nevertheless, efficient multihoming configurations require support from all layers, as for instance in, network protocols which must incorporate mechanisms to support multiple addresses. Multiple Care of Addresses Registration (MCoA) is a protocol that extends Mobile IPv6 to enable the registration of multiple addresses. This paper presents mCoA++, our publicly available simulation model for OMNeT++ which implements the Multiple Care of Addresses Registration protocol recently standardized by IETF. Filling a gap in the MCoA specification, mCoA++ incorporates cross-layer mechanisms that tailor address selection according to application requirements. We evaluate our mCoA++ implementation and compare simulation code performance with xMIPv6. We find that mCoA++ adds multiple care of address support in OMNeT++ without introducing any significant overhead.

In recent years, the ubiquity of multimedia services along with the proliferation of mobile devices and the demand for new audio and video applications are changing the life style of users.The multimedia era is allowing users to create, distribute, and access content in ubiquitous way and cost-effectively, while providers explore new ways to increase their revenues.The efficient delivery of real-time multimedia services over emerging diverse and heterogeneous systems is a challenging research goal.The interoperability of applications, transport and network protocols as well as the demand for improved Quality of Service (QoS), Quality of Experience (QoE), and seamless mobility create new challenges and opportunities for further research on novel communication protocols, architectures, and methods to efficiently support current and future multimedia networking systems.In 2009, the Second International Future Multimedia Networking (FMN 2009) workshop was organized in Coimbra, Portugal and achieved exceptional success attracting 64 submissions from 33 countries.FMN 2009 produced a high quality peer reviewed technical programme with an acceptance rate at around 25% and addressed important aspects of future multimedia systems with a focus on Autonomic Content Networks.Authors of selected papers from FMN 2009 were invited to submit extended versions of their papers in order to be considered for inclusion in this Special issue on Future Multimedia.These papers were peer-reviewed again and then further revised by the authors.

In recent years, the ubiquity of multimedia services along with the proliferation of mobile devices and the demand for new audio and video applications are changing the life style of users. User demands for multimedia access anywhere, anytime from any device are creating new challenges for research communities from both academia and industry. It is expected that video-based services alone will account for 50 percent of all consumer network traffic in 2012 and we will continue to witness the explosive growth in users sharing multimedia content over the Internet. In this context, new network, application, and user-based approaches must be created to deal with such complex multimedia systems. This paper presents some of the recent advances in multimedia networking focusing primarily on areas that have been receiving attention recently and are expected to continue to generate further interests in coming years. These areas include Quality of Experience (QoE) and various related standardization issues, Content Distribution Networks (CDNs), multimedia communications, mobile Multimedia. This paper also briefly highlights some of the major challenges that still need to be addressed to enable the support and delivery of multimedia services anywhere, anytime over highly heterogeneous infrastructures and user terminal devices.

Wireless Mesh Networks (WMNs) are a potentially valuable type of new generation communication systems, that allow wired and wireless networks to be easily integrated. Routing plays a central role in WMNs, due to their multi-hop structure and the need to identify the best routes to the gateways that can provide an acceptable performance for demanding applications such as in triple play services, including traditional data applications, voice, and video over IP. A scheme for scalable routing in Multi-Channel Multi-Radio WMNs has been developed to improve the traffic performance in this callenging scenario, named Cross-layer Routing schEme for scAlable Triple play sErvices (CREATE) in WMNs. CREATE employs a clustering routing scheme which relies on a cross-layer routing metric and on an inter-cluster routing procedure for load balancing. A simulation study to assess the impact of the routing metrics on the different applications that form triple play services was carried out, and provided important insigth to support the choice of the metric to be used on the proposed routing scheme. By combining clustering, inter-cluster load balancing and an interference and load aware routing metric, CREATE has the potential for scalable multi-hop WMNs in the presence of challenging traffic patterns, such as Triple Play Services.

VoIP applications are being widely used in today's networks challenging their capabilities to provide a good quality of experience level to the users. In particular, new wireless broadband technologies, such as WiMAX, are being deployed and need to be evaluated to check the performance levels of VoIP services. The work presented in this paper is a unique contribution assessing the VoIP sessions quality on a real WiMAX test-bed, using UDP/RTP and DCCP transport protocols. VoIP quality is measured according the quality perceived by the end users as well as through conventional network parameters, such as one-way delay and packet loss. The results put in evidence a good quality for VoIP services with 60 simultaneous users in a WiMAX link with resources pre-provisioned. Moreover, in the scenarios tested, DCCP has not shown enhanced performance when compared with UDP/RTP, despite the congestion control mechanisms natively supported.

Although IEEE 802.16 has emerged as one of the major candidates for next generation networks, it is also clear that in the near future the combination of several technologies will be required. In this sense, the support of mobility in heterogeneous environments, addressing broadband wireless, is one of the main requirements in next generation networks. This paper evaluates an architecture based on the recently standardized IEEE 802.21 framework, integrating both mobility and quality of service (QoS) mechanisms, through an advanced mobility scenario using a real WiMAX testbed. This architecture supports seamless mobility in broadband wireless access (BWA) networks, integrates different technologies, such as WiMAX and Wi-Fi, and thus, it is suitable for next generation network environments. The results, obtained through real experimentation of the implemented architecture, show that it is able to provide QoS under dynamic scenarios, with fast integrated QoS and mobility signaling.

The anticipated deployment of IEEE 802.16-based wireless metropolitan area networks (WMANs) will usher a new era in broadband wireless communications. The adoption of the WiMAX technology for remote areas, for example, can address challenging scenarios in a cost-effective manner. While WiMAX Forum documents describe an architecture that inherently supports quality of service and mobility, several areas are left uncovered. We present an architecture which integrates WiMAX, quality of service and mobility management frameworks over heterogeneous networks, developing mechanisms for seamless handovers. Our approach takes into consideration the expected deployment of, on the one hand, the IEEE 802.21 (Media Independent Handover) proposed standard and, on the other, the IETFstandardized Next Steps in Signalling framework. The first contributions of this paper comprise a specification of the mechanisms for make-before-break vertical handovers taking quality of service signalling into account and the integration in a heterogeneous environment. The latter contribution is an empirical evaluation of the proposed architecture using a testbed demonstrator. We quantify the processing delays of the main components in our prototype implementation when a terminal hands over between different access technologies, demonstrating the potential of the proposed architecture.

IEEE 802.16 networks provide mechanisms for QoS support at MAC level, but end-to-end QoS issues are not addressed in detail in the standards. This paper presents an analysis and an experimental validation of a comprehensive solution that describes and implements end-to-end QoS in networks with IEEE802.16e segments. A complete QoS model has been specified, defining the traffic descriptors, the QoS parameters and the resource management functions for networks with WiMAX access. This QoS model has been applied to the next step in signalling (NSIS) protocol suite and its impact has been evaluated on end-to-end QoS when heterogeneous network domains are involved. This work is based on the of results of activities focussed on the study of signalling protocols, carried out within the EU Integrated Project WEIRD (WiMAX extension to isolated research data networks).

Real-time multimedia sessions are now present in our daily live experience, and will be among the most important applications in future generation networks. The distribution of those sessions, towards fixed and mobile users, with Quality of Experience (QoE) assurance is important to attract and keep customers, while increasing the profits of providers. This paper proposes the Quality Level Control for Multi-user Session (QUALITIS) approach to assure the quality level of sessions shared by multiple users (multi-users) in future generation networks. QUALITIS aims to keep sessions with an acceptable quality level and to avoid session blocking. The QUALITIS control is achieved by coordinating Quality of Service (QoS) mapping, QoS adaptation, resource allocation and mobility mechanisms. Performance evaluation was carried out based on simulation experiments and verified the QUALITIS impact on the user's expectation and on the performance of the network.

In a multi-domain Internet that offers quality of service guaranties, there is the need of signaling among the domain entities that are responsible for the management of quality of service. Because different domains have different network protocols and topologies, there is no solution that is able to signal these entities using an off-path approach and, in particular, that is able to interwork with the on-path signaling mechanisms. The HyPath approach extends the NSIS framework and its interactions with the local routing protocols to achieve off- path signaling in these hybrid environments. This document presents HyPath and its evaluation on a test-bed, showing that the mechanisms proposed have the potential to perform off-path signaling without introducing an excessive overhead in the network.

The great demand for real-time multimedia sessions encompassing groups of users (multi-user), associated with the limitations of the current Internet in providing quality assurance, has raised challenges for defining the best mechanisms to deploy the next generation of networks (NGN). There is a consensus that an efficient and scalable provisioning of network resources is crucial for the success of the NGN, mainly in what concerns access networks. Previous solutions for the control of multi-user sessions rely mostly on uncoordinated actions to allocate per-flow bandwidth and multicast trees. This paper introduces a multiuser aggregated resource allocation mechanism (MARA) that coordinates the control of class-based bandwidth and multicast resources in a scalable manner. In comparison with previous work, MARA significantly reduces signaling, state and processing overhead. The performance benefits of MARA are analyzed though simulations, which successfully demonstrated the significant optimization in the network performance.

Ubiquitous broadband Internet access is an important requirement to satisfy user demands and support a new set of real time services and applications. IEEE 802.16, as a broadband wireless access technology, can significantly contribute in this area. It is able to provide high throughput over large distances, with intrinsic QoS support, in line-of-Sight and Non- line-of-Sight environments. This paper discusses a network architecture, based on IEEE 802.16 d compliant equipments, which is able to support real-time services with QoS integration through dynamic configuration of the 802.16 channel, using the NSIS framework. Tests have been carried out to evaluate the QoS performance of the defined architecture, demonstrating that it is perfectly capable of handling and supporting real time services, using dynamic configuration of the 802.16 channel, without introducing an excessive cost in the network.

Mobile WiMAX defines an architecture for metropolitan area broadband wireless access networks based on IEEE 802.16e. One of the most important characteristics of WiMAX is support of applications with different QoS requirements in terms of delay, jitter and bandwidth. We briefly review IEEE 802.16 and the mobile WiMAX network reference model and discuss how IEEE 802.21 can enhance mobility management. Mobile WiMAX is often cited as an important 4G contender. We evaluate via simulation its capacity to support real time applications in high-speed vehicular scenarios and assess the potential of using cross-layer information made available by IEEE 802.21/MIH. Our results indicate that using MIH information allows for the fulfillment of multimedia application requirements. On the other hand, the requirements of such applications are far from being fulfilled when MIH assistant information is not employed.

It is expected that the next generation of networks will provide group communication services to mobile users, independently of the underlying Quality of Service (QoS) model, access and connectivity technologies, which may be different in each domain along the communication path. However, current mobility management schemes have limitations in terms of end-to-end QoS support and connectivity control for sessions crossing heterogeneous networks. This paper presents the Multi-user Session Control (MUSC) mechanism that controls the mobility of multiuser sessions while providing QoS mapping, QoS adaptation and connectivity support in heterogeneous environments with mobile receivers and static senders. Performance evaluation shows the MUSC efficiency to setup sessions inside and between access-networks, by analysing the packet delay and the percentage of packet losses during handovers.

Next generation IP networks are envisioned to be heterogeneous, to provide a wide variety of services, and to support mobility of users with distinct requirements. Moreover, mobile communications are expected to expand from telephony to publish-subscribe services, such as real-time multimedia. With this goal, the University of Coimbra is working with DoCoMo Euro-Labs on a unifying control architecture for multimedia publish-subscribe services over an IP-based mobile system, where our proposal aims to control the quality of service and mobility across heterogeneous networks with no perceived service degradation to the users. This article highlights the requirements of a control architecture for publish-subscribe services, and presents our proposal, called QoS Architecture for Multi-user Mobile Multimedia (Q3M). The main components and functionality of the Q3M architecture are analysed from the user and network perspectives, and some simulation results concerning the analysis of the session setup times are presented.

Smart route control is being increasingly used as a way to dynamically improve the end-to-end performance of the outbound traffic of multihomed stub domains. However, all the solutions available at present have in common two drawbacks which are key motivations for this work. First, all solutions are standalone, so no routing control interactions exist between the domains sourcing and sinking the traffic. The consequences of this lack of interactions are quite coarse route control over the outbound traffic from the domains, and the inability to smartly control how traffic flows into the domains. The second drawback is that all available solutions behave in a fully selfish way, that is, they operate without considering the effects of their decisions in the performance of the network. Given these limitations, we propose to extend the existing route control model from standalone and selfish to a cooperative and social route control model. Our main contribution in this paper is to show that when several route controllers compete for the same network resources, the conventional ones are outperformed by those using a cooperative and social approach and this becomes especially noticeable as the network utilization increases. Our results reveal that it is possible to reduce the frequency of traffic relocations by more than a 50% on average and still obtain slightly better end-to-end traffic performance for delay-sensitive applications. A key advantage is that our extension can be installed and used today by simply performing software upgrades to any of the existing route control solutions.