This paper presents a novel self-supervised path-planning method for UAV-aided networks. First, we employed an optimizer to solve training examples offline and then used the resulting solutions as demonstrations from which the UAV can learn the world model to understand the environment and implicitly discover the optimizer’s policy. UAV equipped with the world model can make real-time autonomous decisions and engage in online planning using active inference. During planning, UAV can score different policies based on the expected surprise, allowing it to choose among alternative futures. Additionally, UAV can anticipate the outcomes of its actions using the world model and assess the expected surprise in a self-supervised manner. Our method enables quicker adaptation to new situations and better performance than traditional RL, leading to broader generalizability.

The Fifth-Generation of Mobile Communications (5G) is intended to meet users' growing needs for high-quality services at any time and from any location. The unique features of Low Earth Orbit (LEO) satellites in terms of higher coverage, reliability, and availability, can help expand the reach of 5G and beyond technologies to support those needs. However, because of their high speeds, a single LEO satellite is unable to provide continuous service to multiple User Equipments (UEs) spread over a large (potentially worldwide) area, resulting in the need for LEO satellite constellations with a high number of satellites and a consequent high amount of satellite handovers (HOs). Moreover, UEs can only acquire partial information about the satellite system and compete for the limited available communication resources of the satellites, requiring the implementation of a decentralized satellite HO strategy to avoid network congestion. In this paper, we propose a decentralized Load Balancing Satellite HO (LBSH) strategy based on multi-agent reinforcement Q-learning, implemented within the software Network Simulator 3 (NS-3). LBSH aims to reduce the total number of HOs and the blocking rate while balancing the load distribution among satellites. Our results show that the proposed LBSH method outperforms the state-of-the-art methods in terms of a 95% drop in the average number of HOs per user and an 84% reduction in blocking rate.

Satellite communications (SatCom) have a role of advanced service enablers in the new virtual networks, following 3GPP specifications. Specifically, the satellite peculiar characteristics are of paramount importance to dynamically activate capabilities, such as multicast and broadcast channels, sudden traffic offloading, capacity bonding, and cost-efficient coverage of uncovered areas. A key aspect to achieve a seamless and efficient integration between satellite and terrestrial infrastructures is to make satellite resource management dynamic and with a centralised control of a single orchestrator that has visibility of the end-to-end network. Considering the adoption of Software Defined Networking (SDN) and Network Function Virtualization (NFV) paradigms and the upcoming 5thgeneration of mobile communications (5G), this paper presents the ongoing work within the European Space Agency (ESA) ANChOR project, whose main output will be a data-driven Network Controller and Orchestrator for SatCom networks. This tool will be based on Artificial Intelligence (AI) / Machine Learning (ML)-based techniques to properly allocate resources exploiting some feedback knowledge of the network and it aims to support different services over 5G integrated satellite-terrestrial networks.

A novel approach is proposed for multimodal collective awareness (CA) of multiple networked intelligent agents. Each agent is here considered as an Internet-of-Things (IoT) node equipped with machine learning capabilities; CA aims to provide the network with updated causal knowledge of the state of execution of actions of each node performing a joint task, with particular attention to anomalies that can arise. Data-driven dynamic Bayesian models learned from multisensory data recorded during the normal realization of a joint task (agent network experience) are used for distributed state estimation of agents and detection of abnormalities. A set of switching dynamic Bayesian network (DBN) models collectively learned in a training phase, each related to particular sensorial modality, is used to allow each agent in the network to perform synchronous estimation of possible abnormalities occurring when a new task of the same type is jointly performed. Collective DBN (CDBN) learning is performed by unsupervised clustering of generalized errors (GEs) obtained from a starting generalized model. A growing neural gas (GNG) algorithm is used as a basis to learn the discrete switching variables at the semantic level. Conditional probabilities linking nodes in the CDBN models are estimated using obtained clusters. CDBN models are associated with a Bayesian inference method, namely, distributed Markov jump particle filter (D-MJPF), employed for joint state estimation and abnormality detection. The effects of networking protocols and of communications in the estimation of state and abnormalities are analyzed. Performance is evaluated by using a small network of two autonomous vehicles performing joint navigation tasks in a controlled environment. In the proposed method, first the sharing of observations is considered in ideal condition, and then the effects of a wireless communication channel have been analyzed for the collective abnormality estimation of the agents. Rician wireless channel and the usage of two protocols (i.e., IEEE 802.11p and IEEE 802.15.4) along with different channel conditions are considered as well.

Offering very large data rates is one of the main objectives of Very High Throughput Satellite (VHTS) systems to boost enhanced Mobile Broadband (eMBB) services in converged 5G-satellite systems. To this end, the exploitation of Q/V frequency bands for the satellite feeder link is a key factor for guaranteeing unprecedented data rates provided that efficient handover algorithms are implemented to counteract link outage events caused by severe weather impairments. Moreover, Quality of Service (QoS) of data flows is typically affected when gateway handover is initiated, hence calling for sophisticated ground segment management solutions. In this light, this paper proposes a novel gateway handover strategy and validates its design through simulation campaigns, whose preliminary results show important performance gains with respect to other solutions available from the existing literature.

The advancements in connected and autonomous vehicles in these times demand the availability of tools providing the agents with the capability to be aware and predict their own states and context dynamics. This article presents a novel approach to develop an initial level of collective awareness (CA) in a network of intelligent agents. A specific collective self-awareness functionality is considered, namely, agent-centered detection of abnormal situations present in the environment around any agent in the network. Moreover, the agent should be capable of analyzing how such abnormalities can influence the future actions of each agent. Data-driven dynamic Bayesian network (DBN) models learned from time series of sensory data recorded during the realization of tasks (agent network experiences) are here used for abnormality detection and prediction. A set of DBNs, each related to an agent, is used to allow the agents in the network to reach synchronously aware possible abnormalities occurring when available models are used on a new instance of the task for which DBNs have been learned. A growing neural gas (GNG) algorithm is used to learn the node variables and conditional probabilities linking nodes in the DBN models; a Markov jump particle filter (MJPF) is employed for state estimation and abnormality detection in each agent using learned DBNs as filter parameters. Performance metrics are discussed to asses the algorithm's reliability and accuracy. The impact is also evaluated by the communication channel used by the network to share the data sensed in a distributed way by each agent of the network. The IEEE 802.11p protocol standard has been considered for communication among agents. Performances of the DBN-based abnormality detection models under different channel and source conditions are discussed. The effects of distances among agents and of the delays and packet losses are analyzed in different scenario categories (urban, suburban, and rural). Real data sets are also used acquired by autonomous vehicles performing different tasks in a controlled environment.

This paper presents a novel network architecture for an integrated nanosatellite (nSAT)-5G system operating in the millimeter-wave (mmWave) domain. The architecture is realized adopting a delay/disruption tolerant networking (DTN) approach allowing end users to adopt standard devices. A buffer aware contact graph routing algorithm is designed to account for the buffer occupancy of the nSATs and for the connection planning derived from their visibility periods. At the terrestrial uplink, a coded random access is employed to realize a high-capacity interface for the typically irregular traffic of 5G users, while, at the space uplink, the DTN architecture is combined with the contention resolution diversity slotted Aloha protocol to match the recent update of the DVB-RCS2 standard. To achieve a reliable testing of the introduced functionalities, an accurate analysis of the statistic of the signal to interference-plus-noise ratio and of the capture probability at each mmWave link is developed by including interference, shadowing, fading, and noise. The application of the designed architecture to data transfer services in conjunction with possible delay reduction strategies, and an extension to inter-satellite communication, are finally presented by estimating the resulting loss/delay performance through a discrete-time discrete-event platform based on the integration of Matlab with Network Simulator 3.

HTTPS enhances end-user privacy and is often preferred or enforced by over-the-top content providers, but renders inoperable all intermediate network functions operating above the transport layer, including caching, content/protocol optimization, and security filtering tools. These functions are crucial for the optimization of integrated satellite-terrestrial networks. Additionally, due to the use of end-to-end and per- session encryption keys, the advantages of a satellite's wide- area broadcasting capabilities are limited or even negated completely. This paper investigates two solutions for authorized TLS interception that involve TLS splitting. We present how these solutions can be incorporated into integrated satellite- terrestrial networks and we discuss their trade-offs in terms of deployment, performance, and privacy. Furthermore, we design a solution that leverages satellite broadcast transmission even in the presence of TLS (i.e. with the use of HTTPS) by exploiting application layer encryption in the path between the satellite terminal and the TLS server. Our findings indicate that even if no other operation than TLS splitting is performed, TLS handshake time, which involves roundtrips through possibly a Geosynchronous satellite, can be reduced by up to 94%. Moreover, by combining an application layer encryption solution with TLS splitting, broadcast transmissions can be exploited as well as proactive caching, content pushing, request aggregation, and other optimizations.

Multiple distributed controllers have been used in software-defined networks (SDNs) to improve scalability and reliability, where each controller manages one static partition of the network. In this paper, we show that dynamic mapping between switches and controllers can improve efficiency in managing traffic load variations. In particular, we propose balanced controller (BalCon) and BalConPlus, two SDN switch migration schemes to achieve load balance among SDN controllers with small migration cost. BalCon is suitable for the scenarios where the network does not require a serial processing of switch requests. For other scenarios, BalConPlus is more suitable, as it is immune to the switch migration blackout and does not cause any service disruption. Simulations demonstrate that BalCon and BalConPlus significantly reduce the load imbalance among SDN controllers by migrating only a small number of switches with low computation overhead. We also build a prototype testbed based on the open-source SDN framework RYU to verify the practicality and effectiveness of BalCon and BalConPlus. Experiment confirms the results of the simulations. It also shows that BalConPlus is immune to switch migration blackout, an adverse effect in the baseline BalCon.

Satellite constellations are envisioned as meaningful transport networks to forward data throughout the world. Low Earth Orbit (LEO) satellites are the most appealing for this purpose due to their low altitude which allows guaranteeing certain performance, especially in terms of delivery time. Mega-constellation of small LEO satellites (micro- and nano-satellites) are planned to be employed to cover the entire Earth's surface. However, these satellites have several constraints which affect the data forwarding process and have to be taken into account. Energy is one of these constrained resources. Energy storage and recharge are limited by the reduced battery capacity and solar panel surface area, while telecommunication hardware energy consumption is considerable especially in case of high traffic volumes. In this paper, we propose a novel energy-aware routing algorithm based on the Contact Graph Routing (CGR) called E-CGR. E-CGR exploits static and known a priori information about contacts (begin times, end times, and overall contact volumes) to compute complete routing paths from source to destination which are then validated and confirmed from the energy viewpoint.

Recently, random access protocols have acquired a new wave of interest, not only from the satellite communication community, but also from researchers active in fields, such as Internet of Things and machine-to-machine. Asynchronous (slot- and frame-wise) ALOHA-like random access protocols, are very attractive for such applications, enabling low complexity transmitters and avoiding time synchronization requirements. Evolutions of ALOHA employ time diversity through proactive replication of packets, but the time diversity is not fully exploited at the receiver. Combining techniques, as selection combining and maximal-ratio combining, are beneficial and are adopted in the enhanced contention resolution ALOHA (ECRA) scheme, presented here. A tight approximation of the packet loss rate for asynchronous random access, including ECRA, well suited for the low channel load region is derived. Finally, ECRA is evaluated in terms of spectral efficiency, throughput and packet loss rate in comparison with recent protocols, showing that it is able to largely outperform both slotted synchronous and asynchronous schemes.

The number of nanosatellites orbiting around the Earth is increasing year after year. Nanosatellite constellations can be deployed to cover even larger areas. However, data exchange among nanosatellites is not trivial, especially due to the required hardware components related to the limited size and weight. Moreover, in some cases, contacts between nanosatellites and ground stations cannot always be guaranteed. The Delay and Disruption Tolerant Networking (DTN) paradigm allows storing data in nanosatellite and ground station buffers until the contact with the next hop is available. Routing in this kind of network is a crucial aspect. Delivery times are larger compared to a ``classical'' network due to the time that data have to wait inside intermediate node buffers and to the limitation of available resources, especially on- board nanosatellites. The adoption of a smart routing strategy can contribute relieving this gap. In this paper, we propose S-CGR, a Source routing algorithm based on the Contact Graph Routing (CGR). It computes a routing path from source to destination nodes for each bundle, which is the data unit in DTN networks. S-CGR considers static and known a priori information about contacts (begin times, end times, and overall contact volumes) and dynamic information about nanosatellite buffer occupancies and available contact volumes. The complete source/destination paths are stored in the bundles. Intermediate nodes read the routing instructions from the bundles without any computational effort.

Scalability and reliability are among the main concerns in large-scale Software Defined Networking (SDN) application scenarios. A common approach is to use multiple distributed controllers, each managing one static partition of the network. In this paper, we show that dynamic mapping can improve efficiency in managing traffic load variations. We then propose BalCon (Balanced Controller): an algorithmic solution designed to tackle and reduce the load imbalance among SDN controllers through proper SDN switch migrations. Simulations demonstrate that BalCon is lightweight from the computational point of view and reduces the load imbalance among SDN controllers (expressed as variance) by 40% by migrating only a small number of switches. We also built a realistic prototype of SDN controller, BalConController, based on the open-source SDN framework RYU.

Nanosatellites offer a solution to provide Internet access in areas where there is no ICT infrastructure, such as rural and remote areas, keeping low construction and maintenance costs. A nanosatellite constellation is composed of a certain number of nanosatellites distributed in one or more orbital planes. In most cases, this network cannot ensure an end-to-end connection between sources and destinations, because not all satellite links are up at the same time. The Delay and Disruption Tolerant Networking (DTN) paradigm is so necessary to deal with predictable disruptions and large delays, allowing nanosatellites, Internet gateways (also called hot spots), and rural gateways (also called cold spots) to keep data stored in their buffers also for tens of minutes waiting to be forwarded. We focused our attention on a possible selection strategy which indicates to all nanosatellites how many bundles (PDUs of the DTN protocol) they can upload from rural gateways during each contact. The decision is made by considering the maximum amount of data that nanosatellites and cold spots can exchange during each contact (quantity related to contact durations) and the possible presence of congestion situations in rural and remote areas or in nanosatellites. The proposed strategy is called ColdSel: it calculates the amount of bundles that each cold spot has to upload on the nanosatellite in contact with in order to mitigate congestion situations in rural areas and nanosatellites and to reduce the nanosatellite buffer occupancies so improving the performance in terms of data delivery time.

The design of High Throughput Satellite (HTS) systems builds on the concept of Smart Gateway Diversity (SGD) to exploit the spatial diversity of gateways in case of feeder link outage, occurring because of atmospheric impairments introduced in Extremely High Frequency (EHF) frequency bands. The gateway handover procedure requires precise prediction algorithms and coordination among different network elements. This paper presents novel outage prediction algorithms based on machine learning concepts, integrated in the framework of SDN architectures, to efficiently orchestrate the gateway handover operations. Simulation campaigns prove the validity of the proposed concept and shed light on the potentials of the SDN architecture in future HTS systems.

Nowadays, to benefit from Internet access is so easy in some areas of the world as difficult in others. There are some different projects whose purpose is to extend Internet access to areas which do not have it yet. Each of these projects has unique characteristics that distinguish it from others (different transmission channels, different devices used, \dots). One possible solution provides the use of a particular type of satellites called nanosatellites. Using these devices, we can have a solution to extend the network access in rural and remote areas which offers a good balance among performances, security and costs. In a network of this type ground stations (called hot spots) are deployed, which upload data destined to rural areas on nanosatellites and download data destined to Internet servers from nanosatellites. During a data connection, an Internet server that wants to reply to a request coming from a rural area has many hot spot alternatives to whom it can deliver data. The problem of choosing the ``optimal'' hot spot becomes important because a wrong choice could lead to a high delivery delay. We propose ``HotSel'': a hot spot selection algorithm able to minimize data delivery time. HotSel is simple and practical, and outperforms two other selection mechanisms used as comparison. All results have been collected by using Network Simulator 3 (NS3) and developing a module able to simulate a nanosatellite network.

This paper considers video transmissions through Smartphones in scenarios of emergency networks where satellite links are employed. Unfortunately, satellite channels may be affected by attenuation and fading, causing significant and frequent variations of the link quality. For this reason, static compression, coding and resource allocation are not optimal solutions to guarantee a satisfactory level of Quality of Experience: we propose to apply two techniques: i) a dynamic transmission rate allocation able to assign resources to the links according to their conditions; ii) an application layer joint coder for video transmission capable of adaptively compressing and protecting the transmitted video frames so recovering losses. The performance investigation of the proposal has been carried out through emulation and the obtained results are satisfactory and open the doors to future development of the proposal.

In this paper, an Android SPEech proCessing plaTform as smaRtphone Application (SPECTRA) is presented. Such application, developed by the authors, has three main functions: i) Gender Recognition (GR), ii) Speaker Recognition (SR) and iii) Language Recognition (LR). All these recognition functions are performed simultaneously by using unsupervised Support Vector Machine (SVM) classifiers. An innovative point of this paper lies in the automatic re-training of the employed SVMs which are able to dynamically update themselves when a (new) audio from a (new) speaker is provided. This allow to build more robust classifiers, which results in better recognition performances. In terms of accuracy, the GR reaches about 98% of correct classifications, SR performs around 80% while LR shows an accuracy of about 74%.

Often copyrighted multimedia files are uploaded and shared online. To avoid the unregulated spread of such material many copy detectors have been developed in order to deny the possibility to upload, and consequently make available, copies of copyrighted contents. A widely referenced fingerprint method for content-based audio identification is the Philips Robust Hash (PRH) . This paper introduces a simple but effective attack technique capable to defeat a PRH fingerprint-based audio copy detector without significantly affecting the signal quality. It is a heuristic method that adds a suitable distortion to the original audio signal, so that the modified signal is not detected as a copy of the original one but is perceptively very similar to it. The quality of the modified signal has been evaluated in terms of a distortion measure based on a mathematical model of the human auditory system and of the Peak Signal-to-Noise Ratio (PSNR). The attack method has shown a promising success rate.

Recently, people have been interested in sharing what they are watching on TV, allowing the development of Social TV Applications often based on mobile devices. In this context, this paper proposes IRTR (Improved Real-Time TV-channel Recognition): a new method aimed at recognizing in real time (live) what people are watching on TV without any active user interaction. IRTR uses the audio signal of the TV program recorded by smartphones and is performed through two steps: i) fingerprint extraction and ii) TV channel real-time identification. Step i) is based on the computation of the Audio Fingerprint (AF). The AF computation has been taken from the literature and has been improved in terms of power consumption and computation speed to make the smartphone implementation feasible by using an ad hoc cost function aimed at selecting the best set of AF parameters. Step ii) is aimed at deciding the TV channel the user is watching. This step is performed using a likelihood estimation algorithm proposed in this paper. The consumed power, computation and response time, and correct decision rate of IRTR, evaluated through experimental measures, show very satisfying results such as a correct decision rate of about 95%, about 2s of computation time, and above 90% power saving with respect to the literature.

Telemedicine applications provide healthcare services through communications technologies overcoming the geographical separation between patients and caregivers. These services can be provided via wireless devices, such as smart-phones with dedicated applications. An interesting application concerns the so-called situation awareness algorithms and, in particular, the Activity Recognition (AR) aimed at tracking the physical activity (or movements) of patients that need a constant monitoring of their medical conditions. This work takes as reference an architecture applicable, but not limited to, patients suffering from Heart Failure (HF) and presents a performance comparison between AR approaches based on the accelerometer signal captured through the patients' smartphones. In more detail, the considered AR techniques apply two different classifiers used to decide the patients movements: a J48 decision tree and a Support Vector Machine (SVM). For each classifier, three different features sets, characterizing the accelerometer signal, have been employed. The performance are evaluated both in terms of accuracy-related metrics and time needed by each classifiers to perform the decision. The results show that SVM provides the best accuracy while the J48 requires less classification time.

The Vertical Handover and the related Network Selection process play a fundamental role in supporting reliable communications over MANETs. The goal of the Network Selection is to determine the Radio Access Network (RAN) that a Mobile Node (MN) has to use among several available RANs. This decision process finds out the RAN that fits the MN requirements and has to provide the decision as rapidly as possible. A computationally heavy Network Selection algorithm can impact the whole handover process because it waits until the selection is carried out. This waste of time can have negative consequences in the quality of communications. The main contribution of this paper is the definition of a new Network Selection algorithm based on a different formulation of the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method found in the literature, called Dynamic-TOPSIS (D-TOPSIS). It is aimed at performing the same selection of the TOPSIS but with a significant reduction of necessary computational load. Finally, the numerical results highlight the execution time reduction obtained by applying the D-TOPSIS with respect to the standard algorithm, and other Network Selection techniques usually applied within Vertical Handover Processes.

The deployment of terrestrial/satellite networks, plays a crucial role for for risk and emergency management. In this context, efficient solutions for heterogeneous and mobile networks, including satellite portions that allows wide coverages, represents a key issue. In the mentioned scenario, transmitting video with portable devices (such as smartphone), over terrestrial/satellite networks, to a Remote Monitoring Host (RMH) may support emergency and rescue operations after crisis situations. Unfortunately heterogeneity often implies impairments such as packet losses, due to errors and congestion, which negatively affect the video quality. We present an application layer joint coding algorithm for video transmission, that adaptively applies video compression and channel coding at the application layer, on the basis of the overall network condition estimated in terms of maximum allowable throughput of the network and quality (packet cancellations or lossiness). A deep performance investigation, carried out with real implementation of the algorithm, compares the joint coding against fixed schemes and shows that the joint approach adapt the video transmission to terrestrial/satellite emergency networks so allowing a more efficient resource exploitation.

The paper deals with the classical problem of the resource allocation in geostationary satellite scenarios where fading may negatively impact the communications. In more detail, we consider the case in which different performance metrics, such as Packet Loss and Power, are simultaneously taken into account. Starting from the wide literature in the field, this work tries to categorize the available and well-known resource allocation approaches into three groups: i) the capacity maximization with constrained power group, ii) the power minimization with constrained capacity group and iii) the multi-objective programming group. For each group a general mathematical formulation has been proposed and the main differences among the groups have been highlighted. The performance of the three listed groups are compared through simulations where two Earth Stations, afflicted by different fading conditions, have been considered. The comparison takes into account all the mentioned metrics (i.e., loss and power) and the computational complexity of the allocation approaches.

This paper considers IRTR (Improved Real-Time TV-channel Recognition), a new method aimed at recognizing in real-time (live) what people is watching on TV, similarly to the action performed by Audience investigations, but without any TV user active interaction. IRTR uses only the audio signal of the TV program recorded through smartphones and is independent of the specific smartphone technology. It is performed through two main steps: i) fingerprint extraction and ii) TV channel real-time identification. This paper proposes a likelihood estimation-based algorithm aimed at performing the second step. The computational time of the proposed approach has been evaluated through real measures and shows really satisfying results.

This paper proposes a new location recognition algorithm for automatic check-in applications (LRACI), suited to be implemented within Smartphones, integrated in the Cloud platform and representing a service for Cloud end users. The algorithm, the performance of which is independent of the employed device, uses both global and hybrid positioning systems (GPS/HPS) and, in an opportunistic way, the presence of Wi-Fi access points (APs), through a new definition of Wi-Fi FingerPrint (FP), which is proposed in this paper. This FP definition considers the order relation among the received signal strength (RSS) rather than the absolute values. This is one of the main contributions of this paper. LRACI is designed to be employed where traditional approaches, usually based only on GPS/HPS, fail, and is aimed at finding user location, with a room-level resolution, in order to estimate the overall time spent in the location, called Permanence, instead of the simple presence. LRACI allows automatic check-in in a given location only if the users' Permanence is larger than a minimum amount of time, called Stay Length (SL), and may be exploited in the Cloud. For example, if many people check-in in a particular location (e.g., a supermarket or a post office), it means that the location is crowded. Using LRACI-based data, collected by smartphones in the Cloud and made available in the Cloud itself, end users can manage their daily activities (e.g., buying food or paying a bill) in a more efficient way. The proposal, practically implemented over Android operating system-based Smartphones, has been extensively tested. Experimental results have shown a location recognition accuracy of about 90%, opening the door to real LRACI employments. In this sense, a preliminary study of its application in the Cloud, obtained through simulation, has been provided to highlight the advantages of the LRACI features.

Optimality conditions for Call Admission Control (CAC) problems with nonlinearly constrained feasibility regions and K classes of users are derived. The adopted model is a generalized stochastic knapsack, with exponentially distributed interarrival times of the objects. Call admission strategies are restricted to the family of Coordinate-Convex (CC) policies. For K = 2 classes of users, both general structural properties of the optimal CC policies and structural properties that depend on the revenue ratio are investigated. Then, the analysis is extended to the case K > 2. The theoretical results are exploited to narrow the set of admissible solutions to the associated knapsack problem, i.e., the set of CC policies to which an optimal one belongs. With respect to results available in the literature, less restrictive conditions on the optimality of the complete-sharing policy are obtained. To illustrate the role played by the theoretical results on the combinatorial CAC problem, simulation results are presented, which show how the number of candidate optimal CC policies dramatically decreases as the derived optimality conditions are imposed.

The task of a capacity allocation policy is to determine the optimal quantity of capacity that has to be shared among the transmitting entities. In this work the allocation problem is modelled by the Multi Objective Programming (MOP) theory. In particular, an allocation criterion based on the Lp-problem is proposed to find out a capacity allocation, among Earth Stations, representative of a compromise if Packet Loss Probability and Transmitted Power are taken into account as performance metrics. The paper also discusses the existence of a capacity allocation, called Capacity Bound, on which the performance converges independently of the overall capacity available CTOT. A performance analysis, carried out through simulations and under different satellite channel conditions, is finally proposed to investigate the allocation criterion performance and to show the Capacity Bound existence.

Recent multimedia and location-based services (LBSs) employ information about location, orientation and context of a mobile device. Moreover, the wide spread adoption of Smartphones, usually equipped with powerful processors, accelerometers, compasses and Global and Hybrid Positioning Systems (GPS/HPSs) receivers, has favored the increasing of location- and context-based services over the last years. In this work a novel Location Recognition approach aimed at supporting location aware services, in particular Check-In services, is presented. The proposed method uses both the GPS/HPS positioning information and, in an opportunistic way, the presence of Wi-Fi Access Points (APs). The method is based on the concept of radio FingerPrint (FP) whose definition proposed in this paper, to the best of authors' knowledge, has never been applied previously. The method is suited to be employed where traditional approaches - usually based only on GPS/HPS - fail, as in case of indoor or dense urban environments. Finally, the proposal, practically realized over different Android OS Smartphones, has been tested in terms of performance. The experimental results are very satisfying and open the doors to a wide employment of the method.

The authors consider the acquisition of measurements from a source, representing a physical phenomenon, by means of sensors deployed at different distances, and measuring random variables (r.v.'s) that are correlated with the source output. The acquired values are transmitted over a wireless channel to a sink, where an estimation of the source has to be constructed, according to a given distortion criterion. In the presence of Gaussian random variables (r.v.'s) and a Gaussian vector channel, the authors are seeking optimum real-time joint source-channel encoder–decoder pairs that achieve a distortion sufficiently close to the theoretically optimal one, under a global resource constraint, by activating only a subset of the sensors. The problem is posed in a team decision theoretic framework, and the optimal strategies are approximated by means of neural networks. The analysis investigates the generalisation capabilities of the proposed approach, by showing insights into the structure of the problem. The surprising outcome is that a quasi-static application of the approach reveals to be sufficient to maintain quasi-optimal performance under a dynamic environment (e.g. with respect to nodes' positions).

In this paper a method to realize the joint application layer coding for image transmission over deep space channels has been presented. In more technical detail, both image compression, based on algorithms such as JPEG2000 and CCSDS, and encoding techniques, such as LDPC codes, to protect the sent images are simultaneously applied by the proposed mechanism. It acts on the bases of the deep space channel conditions, in terms of Bit Error Rate, and it is based on the Multi-Attribute Decision Making theory. In practice, the proposal is aimed at protecting the essential informative contents of images sent through a deep space network and, at the same time, allows minimizing the load offered (the total amount of data to transmit) by the overall application layer coding process to the deep space network. The presented mechanism has been tested through simulations. The obtained results show the effectiveness of the proposal and open the door to further developments of the method in real systems.

This paper shows a detailed performance evaluation of the bandwidth allocation algorithm presented in [1] by the same research group and briefly reminded here. Telecommunications networks are composed of functional layers acting in cascade. The mentioned algorithm adapts the bandwidth to be allocated to a buffer which conveys heterogeneous traffic in a layer-in-cascade functional model, is based only on measures and does not use closed-form expressions, a-priori information about traffic statistical properties, and assumptions about buffer dimension. It is called RCBC (Reference Chaser Bandwidth Control) in [1]. The performance evaluation presented here is aimed at getting a general validation by testing RCBC over multiple DVB-based satellite scenarios and by analyzing the robustness of the algorithm against parameter variations. The performance evaluation is carried out through multiple performance metrics and, in consequence, the results are interpreted through MADM (Multi Attribute Decisions Making) theory, which is appropriate to take decisions in presence of multiple performance indicators.

The paper studies a protocol and a control architecture aimed at implementing bandwidth and call admission optimization over a DVB Return Channel Satellite Terminal (RCST) under Quality of Service (QoS) contraints. The approach can be applied in all cases where traffic flows, coming from a terrestrial portion of the network, are merged together within a single DVB flow, which is then forwarded over the satellite channel. The exact bandwidth to be provided to the flows entering the DVB layer is unknown because equivalent bandwidth techniques guarantee only approximate solutions in heterogeneous conditions. The paper firstly outlines merging operations of the flows over the DVB system and then it specifies the entities to be used at layer 3 and layer 2 of the RCST to coordinate the necessary actions to guarantee the QoS with minimum resource allocation.

Necessary optimality conditions for Call Admission Control (CAC) problems with nonlinearly-constrained feasibility regions and two classes of users are derived. The policies are restricted to the class of coordinate-convex policies. Two kinds of structural properties of the optimal policies and their robustness with respect to changes of the feasibility region are investigated: 1) general properties not depending on the revenue ratio associated with the two classes of users and 2) more specific properties depending on such a ratio. The results allow one to narrow the search for the optimal policies to a suitable subset of the set of coordinate-convex policies.

Satellite communications are characterized by long delays, packet losses, and sometimes intermittent connectivity and link disruptions. The TCP/IP stack is ineffective against these impairments and even dedicated solutions, such as performance enhancing proxies (PEPs), can hardly tackle the most challenging environments, and create compatibility issues with current security protocols. An alternative solution arises from the delay- and disruption-tolerant networking (DTN) architecture, which specifies an overlay protocol, called bundle protocol (BP), on top of either transport protocols (TCP, UDP, etc.), or of lower layer protocols (Bluetooth, Ethernet, etc.). The DTN architecture provides long-term information storage on intermediate nodes, suitable for coping with disrupted links, long delays, and intermittent connectivity. By dividing the end-to-end path into multiple DTN hops, in a way that actually extends the TCP-splitting concept exploited in most PEPs, DTN allows the use of specialized protocols on the satellite (or space) links. This paper discusses the prospects for use of DTN in future satellite networks. We present a broad DTN overview, to make the reader familiar with the characteristics that differentiate DTN from ordinary TCP/IP networking, compare the DTN and PEP architectures and stacks, as a preliminary step for the subsequent DTN performance assessment carried out in practical LEO/GEO satellite scenarios. DTN security is studied next, examining the advantages over present satellite architectures, the threats faced in satellite scenarios, and also open issues. Finally, the relation between DTN and quality of service (QoS) is investigated, by focusing on QoS architectures and QoS tools and by discussing the state of the art of DTN research activity in modeling, routing, and congestion control.

The features that DTN protocol architecture offers are particularly appealing to handle intermittent links and disruption events, by means of the Custody Transfer option. On the other hand, the implementation of long erasure codes proved to be promising to contrast short fading events in long delay networks, where the high latency makes the use of ARQ schemes less profitable. This paper proposes a protocol design to incorporate long erasure codes into the Bundle Protocol specification. The conducted performance analysis shows the benefits coming from this integrated approach but also points out the possible shortcomings deriving from the saturation of the buffer implemented at the Bundle Protocol layer.

The paper proposes a comparison of two communication paradigms, interplanetary and pervasive, through the analysis of problems, solutions and future challenges. The aim is to show that interplanetary communication is performed through peculiar networks, which, on one hand, use most of the pervasive communication paradigm but, on the other hand, own features that allow the extension of the pervasive network concept. The paper contains an introduction of pervasive networking and of interplanetary communication and presents the future challenges of both focusing on architectures and protocols, taking the new solutions of delay tolerant networking (DTN) as a reference point. The use of new interworking devices, called Extended Gateways, aimed at getting efficient interworking over interplanetary networks by joining the features of QoS and DTN Gateways, is envisaged.

The paper addresses resilience over Ethernet networks using the Rapid Spanning Tree Protocol (RSTP). The topic constitutes an open issue of debate as clear indications on the real RSTP performance can hardly be found from the literature. Actually, the complicated protocol structure makes the analysis intricate and unsuitable for generalization. Moreover, the presence of other resilience algorithms, whose mechanisms and rules are explicitly designed for resilience, solves the problem beyond the application of RSTP. Even though those solutions are actually more efficient than RSTP, they are more expensive. In this perspective, the purposes of this paper are to critically evaluate the intrinsic limitations of RSTP and propose some simple protocol modifications to speed up its performance. The analysis validates the achievable performance as a trade-off between fast reactions and bandwidth overhead.

In view of the dense and complex space network topologies envisioned for the future, the management of congestion control is a prominent issue that deserves a particular attention. Given the challenging peculiarities of interplanetary environments, this paper focuses on the advantages offered by storage-based routing and on potentials of implementing Random Early Detection (RED) and Explicit Congestion Notification (ECN) mechanisms within the Delay Tolerant Network (DTN) architecture. In this light, solutions relying upon the aforementioned concepts have been designed and tested. Preliminary results show that combination of RED and ECN schemes with network-selection strategies for storage-based routing is really promising and outperforms other solutions in terms of reliability, network resource utilisation and power consumption.

Next-generation Internet infrastructures have two specific macroscopic requirements: ubiquity and quality of service guarantee. Satellite and wireless systems can easily guarantee ubiquity but, due to noise and fading, they may fail matching quality of service requirements. Bandwidth Allocation algorithms are often used to smooth the problem but they must be properly designed, tuned and tested before their employment. It is important to fix guidelines to orienteer the design to have a correct evaluation of the results in line with the objectives. The basic idea is that bandwidth allocation should be fair and efficient, but what does it mean? What is the definition of fairness and efficiency? The answer of this article relies on fairness and bandwidth utilization concepts, which are consolidated in the field, and on the idea of performance efficiency, proposed in this article. All of them may be translated in indexes that can be important to evaluate bandwidth allocation algorithms in satellite and wireless environments. This is exactly the aim of this article, which suggests some design and evaluation guidelines for bandwidth allocation schemes based on the mentioned concepts and considers some allocation methodologies proposed in the literature as a reference.

Telecommunications networks are composed of functional layers acting in cascade. Quality of service (QoS) derives from the action of each layer that must assure a specific level of quality to the upper layer in terms of performance parameters. The action is called vertical QoS mapping and is provided through algorithms that compute the bandwidth necessary so to assure the requested QoS when information is transferred from one layer to the next one below. This paper proposes a scheme that adapts the bandwidth to be allocated to a buffer which conveys heterogeneous traffic (both concerning traffic sources and QoS requirements) in a layer-in-cascade model. The proposed algorithm is based only on measures and does not use closed-form expressions, a-priori information about traffic statistical properties, and assumptions about buffer dimension. It is called WI-RCBC (wireless interface reference chaser bandwidth control).

We consider the acquisition of measurements from a source, representing a physical phenomenon, by means of sensors deployed at different distances, and measuring random variables that are correlated with the source output. The acquired values are transmitted to a sink, where an estimation of the source has to be constructed, according to a given distortion criterion. In the presence of Gaussian random variables and a Gaussian vector channel, we are seeking optimum real-time joint source-channel encoder-decoder pairs that achieve a distortion sufficiently close to the theoretically optimal one, under a global power constraint, by activating only a subset of the sensors. The problem is posed in a team decision theoretic framework, and the optimal strategies are approximated by means of neural networks. We compare the solution with the results obtained by heuristically choosing a subset of the sensors on the basis of successive simulations under a fixed topology.

The framework of the work is an environmental monitoring system (EMS) realized by a satellite based sensor network (SSN). The paper introduces and formalizes specific performance metrics needed to implement an efficient Sink selection process (where Sink represents a satellite channel access node) based on a multi-attribute decision making algorithm. It is aimed at enhancing the functionality of the whole EMS in terms of reliability, reactivity and spent energy. The reference metrics are packet loss rate, average packet delay, and energy consumption. The algorithm is tested through simulation.

The networking and communication challenges posed by interplanetary environments make the design and the deployment of complex telecommunication infrastructures particularly difficult, especially with regard to routing and congestion control issues. To this end, the paper proposes a congestion-aware routing paradigm that applies multi attribute decision making (MADM) concepts for next-hop selection, by formulating an optimisation problem and proposing some possible resolution criteria. Effectiveness of the proposed solutions is assessed through a preliminary performance analysis that shows promising results.

Providing effective telecommunication services over interplanetary networks poses a number of open challenges because of severe impairments exhibited in such environment. In this perspective, this work proposes a coding framework, integrated within the delay tolerant network (DTN) architecture, implementing adaptive erasure coding schemes that rely upon partial observation of the transmission channel dynamics. Three main protocol solutions based upon partial observable Markov decision process (POMDP) and incremental redundancy adaptation (IRA) have been devised and analysed under different scenario configurations. The performance analysis showed promising results and the superiority of the proposed solutions with respect to approaches based upon fixed- rate coding strategies.

The paper studies the bandwidth allocation process over satellite communication systems as a multi-objective programming (MOP) problem and evaluates an allocation method called "combined Utopia minimum distance" (combined UMD). The entities of the system are earth stations and, for each of them, a set of performance metrics (represented by specific analytical functions), which compete to access the satellite channel. Combined UMD is aimed at approaching the performance obtained for each performance metric when there is no conflict among them to access the channel. In short, it assigns the bandwidth so to approach a non-competitive situation where each metric "sees" the overall channel bandwidth availability as close as possible. In more detail, in this work two kinds of performance metric have been considered: the packet loss probability, which is a typical QoS metric for the TCP based traffic and the average delay, which is typical for UDP based traffic. The allocation method is tested through the ns2 simulator by using TCP and UDP traffic generators and by varying the fading level of the satellite channel over time. Combined UMD has been compared with other approaches taken from the literature in the field.

Providing effective telecommunication infrastructures for disaster relief and emergency operations can be achieved by taking advantage of anywhere-anytime communication capabilities offered by satellite and wireless technology. In this perspective, designing a network architecture able to ensure reliable and timely delivery of data, and able to resist against link disruption is of utmost importance. To this end, this work proposes a mobility-aided routing strategy, derived from other proposals, that aims at delivering data to destinations by taking into account power consumption issues. The efficacy of the proposed solutions is assessed by simulation, considering different scenario configurations.

The paper proposes a novel measurement-based equivalent bandwidth technique that computes the bandwidth to be allocated to a buffer which conveys heterogeneous traffic (both concerning traffic sources and QoS requirements), without using any closed-form expression. The effectiveness of the algorithm is checked through simulation analysis.

The paper deals with protocol architectures to support mapping of quality of service (QoS) between protocol layers of telecommunication networks. The Technology Independent - Service Access Point studied to this aim within the ETSI committee is summarized and analyzed. Inherent QoS mapping operations introduce the generalization of the regular concept of equivalent bandwidth (EqB). Some performance evaluation is proposed to highlight EqB dimensioning.

The paper studies the performance of possible bandwidth allocation criteria over satellite network. The methods practically implemented in a simulation framework and evaluated are the "value function" (VALUE), the "Nash bargaining solution" (shortly NBS) and the "Utopia minimum distance" (UMD). All the methods, together with two simple approaches introduced for comparison (fixed allocation (FIX) and a Heuristic method (HEU)), have been tested using TCP/IP traffic and the performance evaluation is carried out by varying the degradation level of the satellite channel in different satellite network conditions.

Modern environmental monitoring systems are based on satellite-based sensor networks (SSN) where earth stations (Sinks) gather information from sensors and use the satellite channel to send it to remote sites. For the sake of efficiency of a whole monitoring system, the SSN has to be managed by following two main aims: to guarantee the reliability, in particular in case of failure of the satellite portion of the network, and to limit both delay, which is representative of a very important Quality of Service (QoS) metric, and energy consumption. The dynamic sink selection process may allow reaching both aims of the system. In more detail, the paper proposes: the description of the SSN architecture taken as reference, the quality requirements of the system, a revision of the Sink selection method called LINMAP, and an introductive simulative study of its performance in case of failure of the satellite portion of the system.

The problem of pricing for a telecommunication network is investigated with respect to the users' sensitivity to the pricing structure. A functional optimization problem is formulated, in order to compute price reallocations as functions of data collected in real time during the network evolution. No a-priori knowledge about the users' utility functions and the traffic demands is required, since adaptive reactions to the network conditions are sought in real time. To this aim, a neural approximation technique is studied to exploit an optimal pricing control law, able to counteract traffic changes with a small online computational effort.

The paper analyzes the performance of the bandwidth allocation process over satellite communication systems in presence of specific quality of service (QoS) requirements. The reference allocation algorithms considered are based on multi-objective programming (MOP) and are called "Utopia minimum distance" (UMD), "constrained Utopia minimum distance" (CUMD) and "QoS point minimum distance" (QPMD). The rationale under the algorithms is considering bandwidth allocation as a competitive problem where each earth station has its cost function that needs to be minimized by penalizing the others. The performance of the techniques described has been evaluated over a faded channel by using TCP/IP traffic. The analysis is carried out analytically by comparing the efficiency of the MOP based techniques with other approaches treated in the literature and by evaluating the effects of possible QoS specifications.

Transferring data reliably from Mars to Earth stations is becoming an appealing challenge in the design of interplanetary networks. In this view, the use of CCSDS-based protocols along with erasure codes is a promising candidate for mitigating the performance degradation due to large propagation delays and high packet loss rates. Besides, the constraints imposed on the transmission power and on the available link bandwidth introduce further challenges to the design of the telecommunication system. In this paper, the benefits brought are investigated by tuning properly erasure code rate at the upper layers, pointing out the performance gain in terms of goodput performance and analysing power consumption and bandwidth usage issues, as well.

In this paper, the IEEE 802.16 protocol is investigated with respect to the bandwidth provision problem arising at the medium access control (MAC) layer. The aim is to optimally tune the resource allocation to match QoS requirements. Traffic flows are originated at network layers overlying the 802.16 protocol stack. This leads to the investigation of a novel control algorithm, suited to optimal bandwidth allocation and call admission control in the presence of statistically heterogeneous flows. Specific implementation details are provided to match the application of the control algorithm using the regular 802.16 request-grant protocol. Simulation results validate the proposed approach.

The paper describes a measurement campaign recently carried out by University of Bologna (UoB), National Inter-University Consortium for Telecommunications-(CNIT) and University of California Los Angeles (UCLA), on the CNIT GEO Skyplex platform. The aim of the experiments is the performance assessment of a wide range of TCP enhancements on network environments that include a real GEO satellite link. Measurements were carried out by means of the integrated UoB-CNIT testbed, fully controlled by remote through a Web interface. Analysis of live experiments data confirm the challenges posed by GEO sat channels, and show a negative influence of the Skyplex BoD technique on TCP start-up performance. Among the TCP enhancements compared in the paper, best results are provided by TCP Hybla and TCP Westwood, with an advantage of the former in heterogeneous environments characterized by a high level of RTT unfairness.

The paper introduces and analyzes the bandwidth allocation process over space communication systems, corrupted by rain fading, in presence of quality of service (QoS) constraints. To reach the aim, the work proposes two schemes both aimed at assigning the bandwidth, among earth stations, so to approach the ideal situation as close as possible and at guaranteeing a fixed performance for each traffic flow traversing the space network. The mathematical framework of the paper is the multi-objective programming (MOP) theory and the reference allocation scheme considered is called "minimum distance" algorithm. The performance evaluation is carried out analytically by varying the fading level of the channel and considering TCP traffic sources.

Recent environmental monitoring systems are based on Satellite-based Sensor Networks (SSN) where earth stations (Sinks) gather messages from sensors and use the satellite channel to send sensible information to remote monitoring sites. In these systems, the Sink selection process may play a crucial role and needs to be investigated. The work includes: an introduction of the SSN scenario considered; a brief description of the Sink selection method aimed at guaranteeing the optimization of the energy consumption and, simultaneously, of the message transfer delay; a deep performance investigation, which represents the main contribution of this paper, carried out by simulation, of the studied technique.

The extension of telecommunication frontiers towards deep space scenarios has opened new horizons in the way of designing network infrastructures and has raised the necessity of developing novel communication paradigms, more suited to this specific environment. Under this view, the exploitation of TCP-based transmission schemes does not offer satisfactory results. On the contrary, the use of erasure coding schemes and more appropriate automatic repeat request (ARQ) schemes, available within the transport layer coding-based and the Consultative Committee for Space Data Systems (CCSDS) protocol architectures, respectively, assure better performance results. In this paper, the adoption of erasure codes within CCSDS protocol stack is considered and its effectiveness is evaluated with respect to ARQ-based transmission schemes available within the CCSDS file delivery Protocol.

An optimization problem for QoS mapping over protocol layers is formalized in this work by taking the ETSIsatelliteindependent-serviceaccesspoint(SI-SAP) as technological reference. The joint optimization of loss and delay performance metrics, together with the presence of SI-SAP QoS mapping operations, introduces the generalization of the regular concept ofequivalentbandwidth. This leads to the study of a proper measurement-based control, able to capture the most stringent QoS requirement over time (between loss and delay) and the related instantaneous bandwidth need at the lower layer of the protocol stack. The control methodology is tested through real fading and traffic traces to highlight its effectiveness for real time control of QoS mapping operations.

The paper formalizes the bandwidth allocation process as a Multi - Objective Programming (MOP) problem, revises an algorithm already in the literature (identified as ABASC) in the framework of the MOP and proposes a novel scheme (called Minimum Distance - MD method), which fully uses the MOP features. All the schemes are suited to be used in the High Amplitude Platforms (HAPs) environments and are aimed at improving the level of Quality of Service (QoS) of the communications system. The rain attenuation effect, typical of the HAP channels, is considered and modelled as a reduction of the available bandwidth. Only TCP/IP traffic is considered. The two strategies investigated are compared each other and with a fixed and a heuristic allocation. The performance evaluation is carried out analytically by varying the degradation level of the HAP channel and the traffic load offered to the earth stations.

The reference environment is composed of a sensor network that conveys information towards earth stations (called sinks) that give access to the satellite backbone and, through it, to the destination. The choice of the sink where to convey sensor information may affect the overall communication performance. After introducing the application environment, the paper introduces a method to select the sink that assures the improvement of network performance in terms of energy consumption, load, and total time spent by information packets in the network, considering the fading level measured by earth stations. After selecting the sink, the technique how to propagate information within the sensor network has a main role. The paper compares flooding-based techniques on the basis of the metrics mentioned above.

The rising demand for multimedia services even in hazardous environments, such as space missions and military theatres, and the consequent need of proper internetworking technologies have revealed the inapplicability of TCP/IP architectures and highlighted the importance of the communication features provided by the protocol architectures proposed by the Consultative Committee for Space Data Systems (CCSDS). This paper proposes a CCSDS File Delivery Protocol (CFDP) extension, based on the implementation of erasure coding schemes, in order to assure high reliability to the data communication even in presence of very critical conditions, such as hard shadowing, deep fading periods and intermittent links. Different encoding techniques are considered and various channel conditions, in terms of Bit Error Ratio and bandwidth values, are tested.

The demand of bandwidth for TCP/IP based services is growing significantly and the wireless networks are becoming a frequently employed solution to satisfy it. In the wireless scenario, High Altitude Platform (HAP) communications represent a reality, even if absorption and scattering of radio waves by atmospheric components may affect the performance of the communication system. In particular, rain causes severe attenuation so creating communications detriments. The dynamic bandwidth allocation among earth stations may be part of rain fading countermeasures aimed at improving the level of Quality of Service (QoS). The paper formalizes the bandwidth allocation process as a Multi - Objective Programming (MOP) problem; describes four allocation schemes already in the literature by using the MOP framework and proposes one new algorithm that exploits MOP features: it is called Minimum Distance (MD) algorithm. The allocation strategies described are compared each other to highlight the peculiar characteristics for each of them and to show the performance of MD scheme. The reference metrics are the packet loss probability and the allocated bandwidth.

This paper deals with a NP-hard resource allocation problem for a satellite network. An approach based on the estimation of the gradient of a cost function, obtained through a "relaxed continuous extension" of the discrete constraint set, is proposed. Since neither closed forms of the performance measure, nor additional feedbacks on the statistical properties of the traffic sources are requested, the proposed approach reveals to be suitable for optimizing the resource allocation in real life case studies, where the application of specific certainty equivalent assumptions is impractical

This paper evaluates the effects of bandwidth asymmetry introduced in a geostationary DVB-RCS satellite architecture on the round trip time of the transmission control protocol (TCP). In particular, it shows the analytical approximation of the round trip time (RTT) of a TCP connection and defines a bandwidth asymmetry index, which is the key point of the work. The final goal is the provision of analytical equations approximating the RTT behavior over asymmetric satellite networks in strict dependence on the asymmetry index. It can help design DVB-RCS system and evaluate their performance. The results are compared with the values obtained through the ns-2 simulator

The quality of service (QoS) provision requires the cooperation of all network layers from bottom-to-top. More specifically, in the ETSI broadband satellite multimedia architecture, the physical layers are isolated from the rest by a satellite independent-service access point (SI-SAP). The structure of SI-SAP protocol model "opens the door" to the problem of mapping the performance requests of satellite independent (SI) layers over (SD) satellite dependent technology. In this perspective, we investigate here a novel control algorithm for QoS mapping at the SI-SAP interface. Through the adoption of infinitesimal perturbation analysis, we are able to capture the "bandwidth need" of the different flows when they are conveyed to the SD core. Simulation results validate the proposed approach.

The paper contains the formulation of an analytical expression of the TCP throughput and the packet loss probability over geostationary satellite channels on the basis of the state-of-the-art in the field. This work is based on the most important literature about TCP modeling and analysis. The expression obtained, in closed form, is a function of the bandwidth and buffer queues size available at the satellite gateway. Performance analysis is provided in terms of throughput and packet loss probability. Analytical results are compared with the tests obtained through a satellite network emulator already validated in the literature.

Resource allocation schemes dedicated to satellite environments often considers Internet traffic as the superposition of traffic sources without distinguishing between TCP and UDP flows, even if TCP and UDP imply very different traffic characteristics. The basic idea of this work is that a resource allocation algorithm where the allocation function is conscious of the difference may result more efficient. To reach the aim, the paper introduces: a system control architecture with three types of flows entering the network (constant bit rate (CBR), UDP and TCP) and a cost function including an analytical measure of the packet loss for TCP flows. The work joins the novelties introduced with a bandwidth allocation control already in the literature (called CAP-ABASC) and derives a new allocation scheme called extended-CAP-ABASC. The performance evaluation includes the comparison of the two allocation strategies mentioned above.

In this paper, a novel call admission control (CAC) problem is investigated in relation to the pricing structure of a telecommunication network, in which both guaranteed performance (GP) and best effort (BE) services are offered. The user's sensitivity to the prices is described through utility functions. An original decision making process is studied to decentralize the proposed CAC mechanism. To this aim, a neural approximation technique is investigated to exploit different decision makers, distributed in the network and performing the CAC decisions. Simulation results show how sub-optimal CAC decisions are obtained in a decentralized fashion and with a small on-line computational effort.

A resource allocation problem for a satellite network is considered, where variations of fading conditions are added to those of traffic load. Since the capacity of the system is finite and divided in finite discrete portions, the resource allocation problem reveals to be a discrete stochastic programming one, which is typically NP-Hard. In practice, a good approximation of the optimal solution could be obtained through the adoption of a closed-form expression of the performance measure in steady-state conditions. Once we have summarized the drawbacks of such optimization strategy, we address two novel optimization approaches. The first one derives from Gokbayrak and Cassandras and is based on the minimization over the discrete constraint set using an estimate of the gradient, obtained through a "relaxed continuous extension" of the performance measure. The computation of the gradient estimation is based on infinitesimal perturbation analysis (IPA). Neither closed forms of the performance measures, nor additional feedbacks concerning the state of the system and very mild assumptions about the stochastic environment are requested. The second one is the main contribution of the present work, and is based on an open-loop feedback control (OLFC) strategy, aimed at providing optimal reallocation strategies as functions of the state of the network. The optimization approach leads us to a functional optimization problem, and we investigate the adoption of a neural network-based technique, in order to approximate its solution. As is shown in the simulation results, we obtain near-optimal reallocation strategies with a small real time computational effort and avoid the suboptimal transient periods introduced by the IPA gradient descent algorithm.

There are several QoS technologies available for an Internet service provider to manage guaranteed performance services in a telecommunication network. The study of the possible interactions between the different QoS technologies is currently an open area of research often called, in the literature, QoS mapping. A QoS mapping problem arises when different encapsulation formats are employed to support a fixed QoS with different transport technologies (e.g., ATM, IP). We face this problem in terms of bandwidth management. We adopt a novel control scheme that does not need any closed-form formula for the performance metric and that is able to react to traffic changes.

This paper presents a performance enhancing transport architecture for the satellite environment. This solution improves the network transport performance by overcoming the limits imposed by a transmission control protocol/Internet protocol (TCP/IP)-based stack suite, while maintaining the interfaces offered by it. This is an important issue since TCP/IP is widely used and most of the applications are based on it. The work starts from the state-of-the-art about the transport layer over satellite by distinguishing two alternative frameworks: the black box (BB) and the complete knowledge (CK) approaches. In the former, the network is considered as a "black box" and only modifications in the terminal tools are permitted. In the latter, the complete control of any network element is allowed so as a performance optimization procedure is possible. The proposed architecture [called Performance Enhancing Transport Architecture (PETRA)] is designed in all details using the second approach. PETRA uses network elements, called relay entities, to isolate the satellite portions in case of heterogeneous networks, while a transport layer protocol stack is used to optimize the transport of information over satellite links. A special satellite transport protocol, that is part of the transport layer protocol stack, is used over such links to perform error recovery. Simulation results show that the proposed framework significantly enhances throughput performance.

The paper concerns the study of transmission mechanisms employed in telecommunication environments, where LEO (low earth orbit) orbits are present Several investigations about novel network architectures have been produced in order to individuate the solution that meets all the network requirements and characteristics in terms of delay, reliability and speed. Two types of solutions are proposed: the first one, where the terminals are modified and no additional tool is inserted in the network; the second one, based on a protocol-splitting philosophy. This latter supposes to add special tools called gateways to improve the performance. The effectiveness of the proposed solution is then evaluated by using a software simulator that has been adapted for the communication in the different protocol architectures studied.

The paper presents a general framework and some possible architecture to get a feasible QoS (quality of service) mapping among network portions that use different technologies to provide a fixed service level to the terminal users. In general, there is a strong need to have "communication" among portions implementing different QoS technologies: a proper architecture, functionalities and protocols should be defined. The current work, after stating the framework, tries to propose some architectural solutions and shows a preliminary performance investigation concerning mapping of a specific QoS parameter as bit loss among an ATM and an IP portion.

The paper contains a proposal about the design and implementation of an on-board satellite packet-switching emulator. The paper lists the requirements of the emulator that have been followed for the design and that will represent the guidelines for the implementation of the features not yet concluded. The characteristics of the emulator architecture are described, including motivations, advantages and drawbacks of the architectural choices. Particular attention is given to the need of a having a real-time behavior and an efficient transport of the information. Implementation details are reported. The support to the real-time over the Linux operating system, on which the implementation is performed, and the utilization of virtual tools to model the ACE emulator interfaces and to map the address at the data fink layer are of particular interest. Neither the design or the implementation of the emulator is fully concluded, but some interesting results, essentially about computation for now, are already available and are reported.

The paper begins suggesting a possible framework to classify the different approaches to modify the transport layer (namely, the TCP) over satellite channels. In one case, the satellite network is considered as a black box (Black Box - BB approach). Each modification is performed within the end terminals. In the other case, the satellite network is completely known and the transport layer parameter tuning and the consequent optimization of the overall performance is not independent from the choices followed within the satellite network (Complete Knowledge - CK approach). In both cases a complete parameterization of the algorithms at the transport layer is recommended to allow adaptability in different conditions. Concerning the CK approach, a first analysis proposed concerns the behavior of the queue length at IP layer in the intermediate routers. The IP buffer tuning represents a first step towards the implementation of a new transport protocol (STP - Satellite Transport Protocol) adapted to various satellite environments from LEO to GEO, whose interfaces towards the upper layers will keep the characteristics of the TCP interfaces but whose performance will be strongly improved. A possible generic architecture is reported and some possible solution to be implemented within the network architecture will be shown along with the results obtained by means of real measures in the field.

The paper proposes two alternative bandwidth allocation schemes suited for the Ka-band satellite environment. The aim is to provide a control mechanism to compensate rain fade. The main idea is to consider the effect of the attenuation as a reduction of the bandwidth 'seen' by a single land station and using a supplementary portion of bandwidth to guarantee a rain margin. One of the earth stations involved plays the role of master. It monitors the available resources and contains the centralized network control center, which manages the bandwidth allocation. Both schemes are organized in two hierarchical levels. The upper level, located in the master station, assigns a portion of the overall bandwidth to the earth stations. At each of these, the lower level shares the received portion between guaranteed and non-guaranteed traffic. The allocation mechanisms are aimed at keeping the call blocking probability of the guaranteed traffic below a given threshold and at reducing the packet dropping probability of the non-guaranteed, best-effort traffic. An extensive performance analysis has allowed investigation of the behavior of the two strategies showing the differences between them.

The paper presents a study and a performance analysis of a modified version of the TCP (Transmission Control Protocol) over a GEO (geostationary orbit) satellite link. The round trip time (RTT) is above 500 ms. TCP has not been designed for these network characteristics: the high delay to receive acknowledgements decreases the performance and makes the quality perceived by the users really poor. The performance of TCP may be improved by properly tuning some parameters and modifying algorithms. The behaviour of the protocol with a modified slow start algorithm is investigated on the basis of previous work concerning variations of the buffer length and of the initial congestion window. Configurations that drastically improve the performance (measured by the throughput in bytes/s and by the overall transmission time) are proposed. A real test-bed, composed of two remote hosts connected through a satellite channel is adopted to obtain the results. The analysis has included both the single application case and the multiple application case, where several connections share the satellite link at the same time.

The paper presents an experimental approach to provide a guaranteed quality of service (QoS) over a satellite network based on the Internet protocol (IP). The results obtained represent part of the experimental activity carried out during the second year of the project "Integration of multimedia services on heterogeneous satellite networks", called "ASI-CNIT project". Both subjective metrics as mean opinion score (MOS) and objective metrics, as video and voice packet loss, jitter and transmission rate have been used to investigate the topic and to get proper configurations able to guarantee an high quality of service perceived by the users (PQoS-perceived quality of service). The integrated services approach along with the ReSerVation Protocol (RSVP) has been chosen to reserve the network resources. The measures reported have been obtained by real operative sessions.

The paper proposes a bandwidth allocation scheme adapted for satellite networks. The traffic considered is divided into two categories: guaranteed traffic and non-guaranteed best-effort traffic. The control scheme is aimed at keeping the call blocking probability of the guaranteed traffic below a given threshold and at minimising the packet discarding probability of the best-effort portion in case of degradation of the satellite channel. In that way a minimum grade of service should be guaranteed for both traffic. The allocation scheme is designed as a two-level hierarchical mechanism: the upper level allocates a portion of the overall bandwidth to each station, the lower level shares the received portion between guaranteed and non-guaranteed traffic. The results show the behaviour of the algorithm and its performance.

The paper presents a study and an analysis of the performance offered by TCP over a GEO (geostationary orbit) satellite link. The characteristics of satellite channels (notably the large round trip delay) heavily influence the TCP flow control, which is essentially based on the acknowledgments. The effect is a delay in the acknowledgement reception and, consequently, in the delivery of messages, with respect to cabled networks. The drawbacks of using TCP in a satellite environment may be mitigated by a proper tuning of some TCP parameters. The behavior of the protocol as a consequence of variations in the buffer length of both the transmitter and receiver and in the initial congestion window is investigated in the paper and a proper configuration that drastically improves performance (measured by the throughput in bytes/s and by the overall transmission time) is proposed. Two test environments have been used to evaluate the proposed modifications: a real testbed, composed of two remote hosts connected through a satellite channel, and a satellite network emulator, composed of three PCs (two of them representing two hosts, the third one reproducing the behavior of the satellite link). In both environments, a single ftp-like application designed for the aim has represented the reference application; three different file sizes have been used and the different effect of the tuning depending on the transfer length has been evidenced.

The increasing demand for a variety of new Internet services with different and possibly stringent QoS requirements (i.e. Internet telephony, videoconferencing etc.) requires the design of mechanisms to support QoS guarantees. The current solutions proposed in IETF, RSVP (Resource reSerVation Protocol) and differentiated services, though suitable for many applications, may result inefficient to support real-time services on a call basis. The RSVP is not really scalable and requires substantial changes in the Internet architecture, while differentiated services provide guarantees mostly on a static and permanent basis. In this paper we assume an Internet architecture supporting multiple priorities as needed in differentiated services, and introduce the PCP (phantom circuit protocol), a mechanism that provides a guaranteed bandwidth transport service for circuit oriented connections. The PCP includes a fully scalable call admission control (CAC) and operates on a per call basis. Simulation of the protocol performance for CBR (constant bit rate) traffic under various network conditions show the adherence of the mechanism to theoretical expectations.

An event-driven simulation tool aimed at testing access control mechanisms in an asynchronous transfer mode (ATM) environment is presented. It is dedicated to the behavioural description of an ATM virtual circuit (VC) switch. The purpose is to test resource allocation and call admission control (CAC) strategies; so, only the relevant events for this objective are considered and some important functions (e.g., the switching element) for a complete description of an ATM switch are not explicitly modelled. Along with the description of the simulation tools; some resource allocation and CAC are also reported, and several simulation results are discussed, in order to assess their performance.

The paper presents a scheme for admission control at the call set-up in an ATM node, aimed at minimising the probability of blocking a call and at balancing this probability between traffic classes. The traffic is considered to be divided into traffic classes, characterised by statistical parameters like peak and average bandwidth and by quality of service (QoS) requirements that allow to define a feasibility region: where requirements are guaranteed A model to describe the 'call admission' is proposed: two different cost functions, based on the blocking probability, are defined and minimised, taking into account the 'feasibility region' constraint: the first function is intended to obtain the minimum overall blocking probability, whereas the second is aimed to balance the blocking probability among classes. The maximum number of acceptable calls yielded by each cost function is obtained for each class, by minimising it under stationary traffic conditions. The efficiency of the proposed strategy is tested by simulations and verified by comparing it with other admission schemes.

Management and control of multimedia traffic is considered within a scenario characterized by the presence of different network platforms, exhibiting possibly very different features in terms of quality of service (QoS). In this framework, the needs for control strategies, acting in the user plane at protocol layers above the transport is examined and their goals, possible actions, information bases and location (centralized/decentralized) are discussed. Two specific strategies for QoS control of a multimedia connection involving real time traffic (voice and video) are then introduced; one is based on a backoff procedure at the transmitter, while the other acts upon feedback from the receiver to change some features of the coding algorithm. The joint operation of both control strategies is examined in an experimental environment based on Ethernet networks, interconnected by IP routers.

Dynamic bandwidth allocation among traffic classes with different performance requirements sharing an asynchronous transfer mode (ATM) link is considered as an integrated control problem with a multilevel structure. At the lower level, call admission control rules are applied that maintain a certain grade of service, in terms of cell loss probability and cell delay, given the buffer space and bandwidth assigned to each class; unlike those used in previous works, these rules are derived on the basis of homogeneous (based on similar quantities) measures of the performance requirements. At the higher level, bandwidth shares are periodically recomputed online by an allocation controller, whose goals reflect overall cell loss and refused traffic, as well as overall average delay. These goals are expressed by an optimization problem that is solved by numerical techniques. The whole control system should provide a dynamic feedback controller, capable of reacting in real time to changes in the traffic patterns. Simulation results are presented and are discussed in regard to the efficiency of the admission controllers, the performance of the overall scheme, and the capability of reacting to sudden changes in the load of some traffic class.>