Satellite networks with wide coverage are considered natural extensions to terrestrial networks for their long-distance end-to-end (E2E) service provisioning. However, the inherent topology dynamics of low earth orbit satellite networks and the uncertain network scales bring an inevitable requirement that resource chains for E2E service provisioning must be efficiently re-planned. Therefore, achieving highly adaptive resource management is of great significance in practical deployment applications. This paper first designs a regional resource management (RRM) mode and further formulates the RRM problem that can provide a unified decision space independent of the network scale. Subsequently, leveraging the RRM mode and deep reinforcement learning framework, we develop a topology feature-based dynamic and adaptive resource management algorithm to combat the varying network scales. The proposed algorithm successfully takes into account the fixed output dimension of the neural network and the changing resource chains for E2E service provisioning. The matched design of the service orientation information and phased reward function effectively improves the service performance of the algorithm under the RRM mode. The numerical results demonstrate that the proposed algorithm with the best convergence performance and fastest convergence rate significantly improves service performance for varying network scales, with gains over compared algorithms of more than 2.7%, 11.9%, and 10.2%, respectively.

With lunar exploration attracting global attention, there is a growing interest in the design of relay satellite constellations for future lunar communication systems which is challenged by the huge distance between earth and moon. In this paper, we propose a novel hybrid combined Earth-Moon constellation network structure with Earth-Moon Libration 1/2 (EML1/L2) points Halo orbits, ordinary lunar orbits, and Geostationary Earth Orbit (GEO) to minimize both the total number of satellites and the average per-device Age of Information (AoI) as well as maximizing the coverage ratio of specific lunar surface regions to improve information freshness. This is formulated as a multiobjective optimization problem solved by the Nondominated Sorting Genetic Algorithm-II (NSGA-II). By simulating various constellation configurations, we can obtain the optimal configuration parameters for different total numbers of satellites. The simulation results show that our proposed combined constellation significantly outperforms traditional Walker Star and Delta constellations in both AoI and coverage performance.

In developing Advanced Driver Assistance Systems (ADAS) and Automated Driving Systems (ADS), traffic sign detection is a critical task. However, existing methods face limitations in real-time performance and small-object detection accuracy, partly due to deployment platform constraints. Our proposed Neck-Heavy YOLOv5 (NH-YOLOv5) introduces significant improvements. It features a hybrid data augmentation approach that enhances the detection of small objects. Moreover, a unique neck-heavy network architecture is designed to optimize detection performance without increasing computational complexity. Notably, NH-YOLOv5 is integrated into the digital twin framework of traffic systems. By leveraging the digital twin’s ability to simulate and monitor traffic scenarios in real time, the model can continuously adapt and improve its detection capabilities. Experimental results based on the Tsinghua - Tencent 100K (TT100K) dataset demonstrate that our method achieves a 53% reduction in computation while enhancing accuracy and small object detection ability, making it highly suitable for real-time traffic sign detection in the context of digital twins.

With the burgeoning advancement of mega low earth orbit (LEO) satellite constellations, multi-antenna gateway station (MAGS) has emerged as a key enabler to support extremely high system capacity via massive feeder links. However, the densification of both space and ground segment will lead to reduced spatial separation between links, posing unprecedented challenges of interference exacerbation. This paper investigates graph coloring-based frequency allocation methods for interference mitigation (IM) of mega LEO satellite communication (SatCom) systems. We reveal the characteristics of MAGS interference pattern and formulate the IM problem of mega LEO systems into a K-coloring problem using an adaptive threshold method. Then, we propose a tailored graph coloring algorithm called Clique-Based Tabu Search (CTS), which leverages the unique clique structure brought by MAGSs to achieve outstanding IM performance. Simulation results demonstrate the superiority and effectiveness of the proposed methodology.

With the ever-increasing lunar missions, a growing interest develops in designing data relay satellite constellations for cislunar communications, which is challenged by the constrained visibility and huge distance between the earth and moon in pursuit of establishing real-time communication links. In this work, therefore, we propose an age and coverage optimal relay satellite constellation for cislunar communication by considering the self-rotation of the earth as well as the orbital motion of the moon, which consists of hybrid Earth-Moon Libration 1/2 (EML1/L2) points Halo orbits, ordinary lunar orbits, and Geostationary Earth Orbit (GEO) satellites. In particular, by minimizing both the number of satellites and the average per-device Age of Information (AoI) while maximizing the coverage ratio of specific lunar surface regions, a multi-objective optimization problem is formulated and solved by using a well-designed Nondominated Sorting Genetic Algorithm-II (NSGA-II). The simulation results demonstrate that our proposed hybrid constellation significantly outperforms traditional Walker Star and Delta constellations in terms of both AoI and the coverage of communication.

With the proliferation of massive explorations on Lunar Far-side Surface (LFS), deployments of scientific infrastructures have drawn substantial attentions with the aids of relay satellites for the moon, i.e., China’s "Queqiao", which allows real-time reporting for current status information from the landing equipment and space vehicles. Without suitable constellation with well designed scheduling scheme, it would be very difficult to get timely information if depending only on single Halo relay satellite due to large coverage gap and limited energy budget for the communication links. In this paper, we design a hybrid circular-Halo orbital multi-relay constellation system for the LFS communication by minimizing the average per-device Age of Information (AoI) of users in the earth. In particular, we develop an age-optimal scheduling strategy with constellation design for accessing different relay satellite of constellation by solving a Constrained Markov Decision Process (CMDP) optimization problem to significantly reduce the average coverage gap in LFS area. Simulation results show that the average per-device AoI of the proposed scheduling algorithm with the well-designed constellation could achieve 16.20% less in time than that of single Halo satellite relay system compared with typical algorithms.

Since the requirements of cross-domain/layer communications, the Space-ground Integrated Information Network (SIIN) becomes a strategic research area. To improve the service sustainability and reduce the latency of data transmission, literature works focus on evaluating the status of channels between ground stations and satellites, but underestimate the power of dynamic data allocation for handover management. This paper explores the relationship of data allocation and seamless handover in SIIN to provide high-reliability and service sustainability. We propose a Channel Perceiving-based Handover Management (CPHM) strategy to optimize the utilization of channels and dynamically adjust the data allocation strategy. Specifically, CPHM perceives the motion status of satellites to accurately evaluate their service time and reconstruct connectivities, e.g., altitude, velocity, motion direction, and location. Furthermore, CPHM evaluates the service capability of satellites to generate the strategy of data allocation and dynamically adjust this strategy. Then, to improve utilization of channels, CPHM manages transmission queues according the strategy of data allocation and length of queues. Extensive simulation results show that CPHM outperforms other baseline algorithms in terms of delivery ratio, average delivery latency, and interruption ratio.

In mobile networks, the User Equipment (UE) secures some of the communication with its serving Radio Access Network (RAN) node ("base station") via a set of keys known as Access Stratum (AS) keys. Unfortunately, the level of secrecy of these keys varies with the mobile procedures re-establishing them. To improve the secrecy of the AS keys, we propose minimal changes to 5G & 4G handovers, i.e., the main AS-key establishment procedures. We show the minimality of our changes also via an implementation of one of our protocols in the 3GPP-compliant Open5GCore 5G testbed. We also systematically cross-compare standard handovers with our amended handovers using MobTrustCom: a framework to quantify especially trust but also communication complexity in mobile networks. Moreover, we use Tamarin, a formal security-protocol verification tool, to prove no loss of "classical" security yet an increase in AS-keys' secrecy brought by our improvements to handovers.

This paper proposes an e-diagnosis system based on machine learning (ML) algorithms to be implemented on the Internet of Medical Things (IoMT) environment, particularly for diagnosing diabetes mellitus (type 2 diabetes). However, the ML applications tend to be mistrusted because of their inability to show the internal decision-making process, resulting in slow uptake by end-users within certain healthcare sectors. This research delineates the use of three interpretable supervised ML models: Naïve Bayes classifier, random forest classifier, and J48 decision tree models to be trained and tested using the Pima Indians diabetes dataset in R programming language. The performance of each algorithm is analyzed to determine the one with the best accuracy, precision, sensitivity, and specificity. An assessment of the decision process is also made to improve the model. It can be concluded that a Naïve Bayes model works well with a more fine-tuned selection of features for binary classification, while random forest works better with more features.

Due to inadequate management of Vehicular Ad hoc Networks (VANETs), malicious nodes could participate in communications along with misbehavior, e.g., dropping packets and spreading fake information. Therefore, it is essential to detect misbehavior of internal attackers that will cause network performance degradation (e.g., taking longer time to receive messages or reaching destinations with detours). Apart from the capture of dynamic network topology of VANETs, the social relationship among nodes can also be applied as a relatively stable metric to qualify nodes. This paper proposes a misbehavior detection mechanism based on social relationships, from which nodes determine trust for the receiver or transmitter. Based on the proposed mechanism, road traffic control applications can avoid the interference from malicious nodes. The construction of social relationships depends on the geographic information reflected by the movement of nodes, including contact frequency and trajectory similarity, since the geographic information can accurately indicate the relevance among nodes. In addition to the social relationship, the proposed mechanism also evaluates the data trust from time and spatial factors to reduce the interference of fake data. Finally, the proposed mechanism integrates data trust and social relationships to enable misbehavior detection decisions. Extensive results of simulations show that the proposed mechanism has outstanding malicious nodes detection rates under various proportions of malicious nodes and movement patterns.

Location-based services (LBSs) have gained popularity as a result of the advances in mobile and communication technologies. LBS provide users with relevant information based on their location. In spite of the desirable features provided by LBS, the geographic locations of users are not adequately protected. Location privacy is one of the major challenges in vehicular and mobile networks. In this paper, we analyze the security and privacy requirements for LBS in vehicular and mobile networks. Specifically, this paper covers privacy enhancing technologies and cryptographic approaches that provide location privacy in vehicular and mobile networks. The different approaches proposed in literature are compared and open research areas are identified.

Satellite communications can be used when other communication systems are either destroyed or overloaded. Observation satellites and delay/disruption tolerant networks (DTNs) are technologies that can be interconnected to provide emergency communication for disaster recovery operations. DTNs use a store-carry-forward mechanism to forward messages through intermediary nodes to the destination node. The reliability of relaying messages through multi-hop nodes poses a significant problem in DTNs due to lack of consistent connectivity. These network characteristics make DTNs to heavily rely on the cooperation of neighboring nodes for the successful delivery of packets. However, the presence of malicious or selfish nodes will have a great impact on the network performance. In this paper, we design a decentralized trust management scheme (DTMS) to filter out malicious nodes in DTNs. First, the number of forwarding evidence is combined with the energy consumption rate of the nodes to formulate direct trust. Then, a recommendation trust is computed from the indirect trust, recommendation credibility, and recommendation familiarity. Recommendation credibility and familiarity improve the overall recommendation trust by filtering out dishonest recommendations. A comparative analysis of DTMS is performed against a cooperative watchdog scheme, recommendation based trust model, and spray and wait protocol. The results show that DTMS can effectively deal with malicious behaviors in DTNs including trust related attacks.

Public‐key infrastructure (PKI) is based on public‐key certificates and is the most widely used mechanism for trust and key management. However, standard PKI validation and revocation mechanisms are considered major reasons for its unsuitability for delay/disruption tolerant networking (DTN). DTN requires mechanism to authenticate messages at each node before forwarding it in the network. So, certificate revocation lists (CRLs) being distributed in DTN network will need to be authenticated and validated for issuer certificate authority (CA) at each node. In this study, the authors propose new validation and revocation mechanism which is compliant with DTN semantics and protocols. This study also proposes a new design for CRL in compliance with standard PKI X.509 standard to make the proposed mechanism easy to implement for DTN. The new designed CRL is of reduced size as it contains fewer entries as compared with standard X.509 CRL and also arranges the revocation list in the form of hash table (map) to increase the searching efficiency.

As modern vehicle and communication technologies advanced apace, people begin to believe that the Intelligent Transportation System (ITS) would be achievable in one decade. ITS introduces information technology to the transportation infrastructures and aims to improve road safety and traffic efficiency. However, security is still a main concern in vehicular communication systems (VCSs). This can be addressed through secured group broadcast. Therefore, secure key management schemes are considered as a critical technique for network security. In this paper, we propose a framework for providing secure key management within the heterogeneous network. The security managers (SMs) play a key role in the framework by capturing the vehicle departure information, encapsulating block to transport keys and then executing rekeying to vehicles within the same security domain. The first part of this framework is a novel network topology based on a decentralized blockchain structure. The blockchain concept is proposed to simplify the distributed key management in heterogeneous VCS domains. The second part of the framework uses the dynamic transaction collection period to further reduce the key transfer time during vehicles handover. Extensive simulations and analysis show the effectiveness and efficiency of the proposed framework, in which the blockchain structure performs better in term of key transfer time than the structure with a central manager, while the dynamic scheme allows SMs to flexibly fit various traffic levels.

Communication technologies are very important for disaster management. Satellite network's advantage of large coverage and Mobile Ad hoc Network's (MANET) advantage of high flexibility could be ideal for disaster management. In this paper, the authors propose a novel scheme for providing reliable wireless communications in disaster sites with a hybrid network of terrestrial MANET and satellite network. In comparison with normal wireless routing approaches, i.e. AODV and AOMDV, the proposed scheme could achieve higher packet delivery ratio, higher throughput and lower delay; meanwhile it could also balance traffic loads at gateways to maximum satellite links' utilization.

Abstract This paper presents a comprehensive study of the performance of routing protocols in distributed vehicular networks. We propose a novel and efficient routing protocol, namely cross‐layer, weighted, position‐based routing, which considers link quality, mobility and utilisation of nodes in a cross layer manner to make effective position‐based forwarding decisions. An analytic hierarchy process approach is utilised to combine multiple decision criteria into a single weighting function and to perform a comparative evaluation of the effects of aforementioned criteria on forwarding decisions. Comprehensive simulations are performed in realistic representative urban scenarios with synthetic and real traffic. Insights on the effect of different communication and mobility parameters are obtained. The results demonstrate that the proposed protocol outperforms existing routing protocols for vehicular ad hoc networks, including European Telecommunications Standards Institute (ETSI's) proposed greedy routing protocol, greedy traffic aware routing protocol and advanced greedy forwarding in terms of combined packet delivery ratio, end‐to‐end delay and overhead. Copyright © 2015 John Wiley & Sons, Ltd.

Reducing energy consumption in the Telecom industry has become a major research challenge to the Internet community. Towards this end, numerous research works have been carried out to mitigate the growth of energy consumption through intelligent network control mechanisms. This paper proposes a novel approach to achieving energy efficiency in ISP backbone networks according to dynamic traffic conditions. The main objective is to enforce as many links as possible to go to sleep during the off-peak time, while in event of traffic volume increase, the minimum number of sleeping links should be required to wake up to handle this dynamicity and in a way that this creates minimal or no traffic disruption. Based on our simulations with the GEANT and Abilene network topologies and their traffic traces respectively, up to 47% and 44% energy gains can be achieved without any obstruction to the network performance. Secondly, we show that the activation of a small number of sleeping links is still sufficient to cope with any traffic surge instead of reverting to the full topology or sacrificing energy savings as seen in some research proposals.

In a content delivery network (CDN), the energy cost is dominated by its geographically distributed data centers (DCs). Generally within a DC, the energy consumption is dominated by its server infrastructure and cooling system, with each contributing approximately half. However, existing research work has been addressing energy efficiency on these two sides separately. In this paper, we jointly optimize the energy consumption of both server infrastructures and cooling systems in a holistic manner. Such an objective is achieved through both strategies of: 1) putting idle servers to sleep within individual DCs; and 2) shutting down idle DCs entirely during off-peak hours. Based on these strategies, we develop a heuristic algorithm, which concentrates user request resolution to fewer DCs, so that some DCs may become completely idle and hence have the opportunity to be shut down to reduce their cooling energy consumption. Meanwhile, QoS constraints are respected in the algorithm to assure service availability and end-to-end delay. Through simulations under realistic scenarios, our algorithm is able to achieve an energy-saving gain of up to 62.1% over an existing CDN energy-saving scheme. This result is bound to be near-optimal by our theoretically-derived lower bound on energy-saving performance.

Energy constraint is a crucial factor in wireless sensor networks (WSNs). One of the best solutions for networking in the WSNs is a clustering-based technique to deal with the energy constraint. However, cluster heads (CHs) in such technique tend to consume much more energy than ordinary nodes and, eventually, deplete quickly. In this paper, we propose a clustering technique, included CH selection and rotation, using an event-driven data reporting during continuous data monitoring of ambient. SNs in this technique report only necessary data when data changes exceeding a given threshold. Therefore, clusters are created only upon specific places where such necessary data changes are happening. Furthermore, the clusters are operated as long as the ambient situation is changing. Once the situation becomes stable, the clusters will be reset and every sensor node in these clusters switch to sleep mode in order to conserve energy consumed by CHs and members. Results show that the network lifetime and stability is better than some existing protocols.

The unstable nature of MANETs over different types of wireless topologies and mobility models affects the Quality of Service (QoS) for real time applications such as Voice over IP (VoIP). One of the most efficient signaling systems for VoIP applications is the Session Initiation Protocol (SIP) which is mainly used to initiate, manage, and terminate VoIP calls over different types of IP based network systems. As a part of upgrading to Next Generation Network, MANETs will be considering IPv6 for different types of applications and devices. Therefore, SIP signaling over IPv6 MANETs needs to be investigated with different QoS performance metrics such as bandwidth, packet loss, delay and jitter. In this paper, an evaluation of SIP signaling is conducted for SIP based VoIP calls using GSM voice codec system over MANETs with Static, Uniform, and Random mobility models. This evaluation considered AODV as a reactive routing protocol and OLSR as a proactive routing protocol over both IPv4 as well as IPv6. The evaluation study of SIP signaling examined call setup time, number of active calls, number of rejected calls and calls duration. The results of this study show that, in general, IPv4 has better performance over different types of mobility models, while IPv6 upholds longer delays and poor performance over Random mobility models.

In this paper, we analyze the current binary partition multi-hop broadcast protocol and propose an enhanced solution, namely, Trinary Partition Black-Burst based Broadcast Protocol (3P3B) for Emergency Message (EM) dissemination. 3P3B provides low and constant latency regardless density and size of networks compared to existing solutions. It also enhances message dissemination speed and message progress distance. The main technique in the 3P3B is that 3P3B uses mini-slot DIFS to give a preemptive priority to very urgent EMs and deploys a trinary partition mechanism to select the furthest forwarder of the next communication hop. We prove that 3P3B recues the delay, increases dissemination speed, message progress distance, and outperforms the well-known existing broadcast protocols for EM dissemination in VANET.

Due to sparse network density, geographic routing in Intermittently Connected Networks (ICNs) suffers from challenges for making the feasible routing decision and handling the local maximum problem, which is in contrast with the conventional geographic approaches in Mobile Ad hoc NETworks (MANETs) relying on high network density. In this paper, we firstly explore the Delegation Replication (DR) approach to overcome the limitation of the geometric metric adopted in our proposed Come Phase to promote message replication coming towards destination, requiring pairwise encountered nodes moving towards destination. Regarding the proposed Leave Phase, using DR also enhances to prevent message replication leaving away from destination. In addition, we handle the local maximum problem addressing the mobility of mobile nodes and message lifetime. Considering the temporarily stationary movement via Stop Phase, evaluation results show the advantage of the proposed Come-Stop-Leave (CSL) in terms of delivery ratio, average delivery latency as well as overhead ratio.

Receiving great interest from the research community, Delay Tolerant Networks (DTNs) are a type of Next Generation Networks (NGNs) proposed to bridge communication in challenged environments. In this paper, the message replication probability is proportionally sprayed for efficient routing mainly under sparse scenario. This methodology is different from the spray based algorithms using message copy tickets to control replication. Our heuristic algorithm aims to overcome the scalability of the spray based algorithms, since to determine the initial value of the copy tickets requires the assumption that either the number of nodes is known in advance, or the underlying mobility model follows the Random WayPoint (RWP) characteristic. Specifically, in combining with the assistance of geographic information to estimate the movement range of destination, the routing decision is based on the encounter angle between pairwise nodes, and is dynamically switched between the designed two routing phases, named as geographic replication and replication probability spray. Furthermore, messages are under prioritized transmission with the consideration of redundancy pruning. Simulation results show our heuristic algorithm outperforms other well known algorithms in terms of delivery ratio, transmission overhead, average latency as well as buffer occupancy time.

Optimizing server's power consumption in content distribution infrastructure has attracted increasing research efforts. The technical challenge is the tradeoff between server power consumption and the content service capability on both the server and the network side. This paper proposes and evaluates a novel approach that optimizes content servers' power consumptions in large-scale content distribution platforms across multiple ISP domains. Specifically, our approach strategically puts servers to sleep mode without violating load capacities of virtual content delivery links and active servers in the infrastructure. Such a problem can be formulated into a nonlinear programming model. The efficiency of our approach is evaluated in a content distribution topology covering two real interconnected domains. The simulation has shown that our approach is capable of reducing servers' power consumptions by up to 62.2%, while maintaining the actual service performance in an acceptable scope.

The concept of Delay Tolerant Networks (DTNs) are proposed to facilitate communication in challenged mobile wireless networks using the Store-Carry-Forward (SCF) routing behavior. In this paper, our motivation is to take advantage of geographic routing since it routes message without the knowledge about network topology by using realtime location information, overcoming the challenge of large network topology variation in DTNs. Different from traditional geographic algorithms, our approach only adopts history geographic information due to the difficulty to obtain the realtime location of destination, suffering from sparse network density and high mobility. The key insight of our algorithm is to separate message replication depending on the proximity to the movement range estimated for destination, followed by the proposed scheduling methodology for prioritized transmission between each phase as well as anti-diffusion function for redundancy reduction. Simulation results under the Helsinki city scenario show an improvement comparing with two well known geographic approaches in DTNs, considering delivery ratio, average latency as well as overhead ratio.

Without the assumption of contemporaneous end to end connectivity in challenged wireless networks, Delay Tolerant Networking (DTN) routing is an important research area. The contribution in this paper is to take advantage of the proposed DTN geographic replication to overcome the limitation of topology based utility replication, since message replication is prevented due to the local maximum problem that the utility metric of encountered node is worse than message carrier. In brief, the proposed DTN geographic replication is activated only if the utility replication is unable to route message, this hybrid approach promotes a seamless message replication given limited message lifetime. Borrowing from the concept of gravity, messages are under prioritized transmission for load balancing and achieving less delivery latency. Extensive simulation results show promising improvement of the proposed algorithm in terms of delivery ratio, transmission cost, average latency as well as number of aborted messages.

The emergence of MANET supported applications and the subsequent widespread acceptance is facilitated by the development and availability of cheap wireless Wi-Fi devices. It is on this premise that Flow-Aware Admission Control (FAAC) protocol is designed to improve the throughput assurance of MANET-based applications. The work presented in this paper is an extension of our designed FAAC protocol to guarantee the provisioning of QoS in many mobile scenarios. The source node is designed to maintain multiple paths to each destination with the reliability of the routes maintained through nodes disjointness. The designed FAAC-Multipath protocol is equipped with the intermediate route repair mechanism to enable the intermediate node to carry out route repair locally without contacting the source node. We have illustrated the effectiveness of FAAC-Multipath with the state of the art admission control protocols.

This paper presents a Priority based Routing Protocol (PRP) in Vehicular Ad hoc Network (VANET), according to message types. We focus mainly on a safety messaging application for safe driving in distributed environment, i.e., ad hoc manner. Broadcast based routing protocol is proposed along with priority and position enhancement to provide i) fully distributed routing protocol, ii) different quality of services (QoS) for different types of messages, iii) maximum message dissemination distance per hop. The proposed protocol, PRP, is evaluated using simulation software called OMNeT++. The performance parameters include average MAC delay, percentage of message reception and collision, as well as average message dissemination distance per hop. The results show the PRP achieves both message prioritization and maximum dissemination distance in fully distributed environment.

Packet injection by an attacker can trigger flooding-based DOS attacks. This paper seeks to provide a simple and robust approach to protect the access control, data integrity and sender authentication security services in resource-constrained delay tolerant networks. The aim is to make security protocols providing these mandatory security services resilient to resource exhaustion DOS attacks. To achieve this we propose a hierarchical design based on the use of light-weight and hard to forge cookies. The DOS defense mechanism can proactively identify and discard attack bundles. Compromised insider nodes are identified and isolated.

The concept of Delay Tolerant Networks (DTNs) has been utilized for wireless sensor networks, mobile ad hoc networks, interplanetary networks, pocket switched networks and suburb networks for developing region. Because of these application prospects, DTNs have received attention from academic community. Whereas only a few state of the art routing algorithms in DTNs address the problem of aborted messages due to the insufficient encounter duration. In order to reduce these aborted messages, we propose a routing framework which consists of two optional routing functions. Specifically, only one of them is activated according to the encounter angle between pairwise nodes. Besides, the copies of the undelivered message carried by most of the nodes in the network are more likely to be cleared out after successful transfer, which reduces the number of unnecessary transmissions for message delivery. By means of the priority for message transmission and deletion in case of the limited network resource, the proposed algorithm achieves the high delivery ratio with low overhead as well as less number of aborted messages due to the insufficient encounter duration, thus is more energy efficient.

Privacy, Anonymity, pseudonymity are the debatable terms which on one angle restrict the rights but on other angle open doors for malicious activity.This paper proposes design for a pseudonymised communication which is optimal solution for the privacy issues, where the real identity is hidden from the outside world by using blind signature in a different way of group communication.The protocol is deployed and analysed in extreme environment of Delay Tolerant Networks (DTN), which is overlay on the top of traditional Internet which provides end to end connectivity and characterized with long delay and disruption. A telemedicine application of rural area network is explored to provide source anonymity.The protocol is finally analysed using Dolev Yao model with two different cases and it preserves the original identity of the node.

The framework of Delay Tolerant Networks (DTNs) has recently received an extensive attention and widely implemented, ranging from Wireless Sensor Networks (WSNs) to Interplanetary Networks. It has been applied in military communication, scientific research and exploration. Due to the characteristic of long delay, intermittent disruption, limitation of buffer space and energy, the traditional routing algorithms in the Internet do not perform well in DTNs. Since most of the existing DTN routing algorithms are based on the replication mechanism to achieve the high delivery ratio. In this paper, we propose an asymmetric spray algorithm based on the limited number of replication with the consideration of utility metric. In addition, we also design an adaptive replication function to optimize the dropped messages due to the insufficient encounter duration. Simulation results show the effectiveness of our asymmetric spray approach. In combination with the other designed functions, our proposed algorithm achieve a better performance than the state of the art algorithms.

Opportunistic Networks (ONs) utilize the communication opportunity with a hop-by-hop behavior, and implement communication between encountered nodes based on the Store-and-Forward routing pattern. This approach, which is totally different from the traditional communication model, has received extensive interests from academic community. We consider the ONs are a type of Delay Tolerant Networks (DTNs) since their routing behavior are quite same regardless of the bundle layer protocol. Until currently, a set of congestion control mechanisms have been proposed in Deterministic DTNs, which is mainly implemented in the network with limited mobility or the static network with scheduled disruption interval. However, regarding the networks with large topology variation, known as Opportunistic DTNs, to design a congestion control mechanism is difficult. In this paper, we propose an active congestion control based routing algorithm that pushes the selected message before the congestion happens. In order to predict the future congestion situation, a corresponding estimation function is designed and our proposed algorithm works based on two asynchronous routing functions, which are scheduled according to the decision of estimation function. Simulation results show our proposed algorithm efficiently utilizes the distributed storage to achieve a quite low overhead ratio and also performs well in the realistic scenario.

Researches on multicast has explored security challenges faced by group communications. Multicast transport protocols and multicast security protocols need to work closely to provide reliable and secure multicast services. However, there has been comparatively little work carried out to specify how exactly the two technologies can work together efficiently. In this paper, authors present an example of partially integrating the Timed Efficient Stream Loss-Tolerant Authentication (TESLA) protocol and the File Delivery over Unidirectional Transport (FLUTE) protocol. TESLA provides source authorization and data integrity for multicast groups while FLUTE ensures reliability of the multicast transmission. This paper proposes a loose synchronization mechanism for a unidirectional transmission environment, suited to satellite networks. The proposed algorithm was implemented on a testbed with multicast tunnel between University of Surrey and University of Aberdeen and the results are presented in this paper.

The notion of Quality of Service (QoS) in Delay Tolerant Network (DTN) is different due to the challenging nature of DTN which might suffer from intermittent disconnections and long delays. DTN has scarce resources; therefore, controlling the admissions to these resources is important to best share them among the users according to each user privilege. This paper presents the requirements for QoS in DTN and identifies the DTN flow characteristics metrics. The control and managements of these metrics will enhance DTN QoS. Also this paper proposes an Admission Control model based on local information of the node resource in order to avoid network congestion and enhance network performance.

In satellite networks, voice over IP performance is degraded by long delays and low bandwidth. Both call setup time and quality of service (QoS) for voice calls are affected. Separate studies have been undertaken for these performance metrics. In this paper, we have carried out experiments using different voice codecs to evaluate SIP call setup time and QoS parameters together. The experiments are performed on the satellite network testbed at Centre for Communication Systems Research (CCSR) at University of Surrey. The results present a comparison of different codecs, highlighting their performance.

Multicast research has explored the security challenges faced in group communications. Multicast transport and multicast security need to work in close collaboration to realise a multicast service. However, there has been comparatively little work to combine the two technologies. In this paper the authors, presenting an example of partially integrating Timed Efficient Stream Loss-Tolerant Authentication (TESLA) protocol and the File Delivery over Unidirectional Transport (FLUTE) protocol. TESLA provides source authorization and data integrity for multicast groups. This paper proposes a loose synchronization mechanism for a unidirectional transmission environment, suited to satellite networks. It also analyses the effects on Forward Error Control (FEC) and the congestion control building blocks of FLUTE when used with TESLA.

This paper proposes a novel demand sensitive model (DSM) for tuning price service over SDMB (satellite digital multimedia broadcast) system offering a price discount to large amount of users while maintaining profit for the service provider. The discounted price is determined based on a marginal decision rule using a simple pseudo-linear function of the weight factor and the number of users. For testing the proposed model, an integrated satellite-terrestrial network architecture offering SDMB services to mobile users through the satellite or terrestrial UMTS segment, has been utilized. Simulations have been carried out to show the goodness of the proposed model within the system architecture; moreover the model, based on simple parameters, is very flexible and can be easily integrated in a "price adapter" module making the offered service attractive for end users and in the same time profitable for the satellite operator.

A secure multicast communication is important for applications such as pay-per-view and secure videoconferencing. A key tree approach has been proposed by other authors to distribute the multicast group key in such a way that the rekeying cost scales with the logarithm of the group size for a join or depart request. The efficiency of this key tree approach critically depends on whether the key tree remains balanced over time as members join or depart. In this paper, we present two Merging Algorithms suitable for batch join requests. To additionally handle batch depart requests, we extend these two algorithms to a Batch Balanced Algorithm. Simulation results show that our three algorithms not only maintain a balanced key tree, but their rekeying costs are lower compared with those of existing algorithms.

Secure multicast communication is important for applications such as pay-per-view distribution. LKH has been proposed to distribute a shared secret key in a way that scales efficiently for groups with many members. However, the efficiency of LKH depends critically on whether the key tree remains balanced. For applications such as video streaming or online teaching, several multicast sessions might be related in one way or another. In this paper, we consider the balance of the key tree and treat related multicast sessions as a whole. Our approach shows significant improvement over traditional method and trades off additional rekeying costs for similar computation power at members' side compared to existing related approach. Two optimisations are also proposed to further enhance the efficiency of our algorithm.

Security is an important concern in today's information age and particularly so in satellite systems, where eavesdropping can be easily performed. This paper addresses efficient key management for encrypted multicast traffic transmitted via satellite. We consider the topic of encrypting traffic in large multicast groups, where the group size and dynamics have a significant impact on the network load. We consider life cycle key management costs of a multicast connection, and show for a logical key hierarchy (LKH) how member preregistration and periodic admission reduces the initialization cost, and how the optimum outdegree of a hierarchical tree varies with the expected member volatility and rekey factor. This improves network utilization, but encryption at the network layer can pose problems on satellite links. We, therefore, propose and analyze an interworking solution between multilayer Internet protocol security (IPSEC) and LKH that also reduces key management traffic while enabling interworking with performance enhancing modules used on satellite links.

This paper describes the architecture of a proposed multiparty conferencing system for satellites. Different conferencing models are discussed and compared. A session initiation protocol (SIP)-based conference signaling model and an extension to protocol-independent multicast sparse mode that supports quality-of-service (QoS) in DiffServ networks are proposed, as particularly suitable for multiparty conferencing applications over satellite links. The paper also presents key issues and potential solutions of scalable QoS multicast services for multiparty conferences over satellite. End-to-end QoS parameters for voice and video are measured and analyzed on a prototype.

The Terminal at High Speed for European Stock Exchange USers (THESEUS) is a European research project. THESEUS with its multimedia communications capabilities enables brokers to trade not only with their national stock exchange but also with all the European stock exchanges. This will make secure trading in the stock exchanges more effective through Europe. This paper presents an overview of the THESEUS system design and architecture and the terrestrial, satellite and security field demonstrations.

In this paper we analyse the performance of a medium access control (MAC) protocol which is particularly suited for a scenario with a high number of terminals with very bursty unspecified bit rate (UBR) traffic (e.g. web browsing). In order to guarantee the required quality of service (QoS) requested by the user for all ATM service classes, priorities between the service classes must be implemented. Hence prioritised queueing of requests is proposed. The adaptive MAC protocol was designed to allow statistical multiplexing of ATM traffic over the air interface, especially for independent and spatially distributed terminals. It is shown that the potential user population which can be served is considerably increased by statistically multiplexing bursty traffic over the air interface.