Real-time applications (RTA) tend to play a crucial role in people's everyday life. Such applications are among the key use cases for the next generations of wireless technologies. RTA applications are characterized by strict guaranteed delay requirements (in the order of a few milliseconds). One of the pillars of enabling RTA in next-generation Wi-Fi standards is Restricted Target Wake Time (R-TWT), which provides Wi-Fi stations exclusive channel access within negotiated service periods (SPs). If each RTA data flow uses dedicated SPs for data transmission, they are completely isolated from each other and do not experience any contention. To ensure the satisfaction of RTA QoS requirements while minimizing the channel airtime consumption, it is important to properly select the R-TWT pa-rameters, namely the duration of SPs and the period between SPs. In this paper, we develop a mathematical model that estimates the delay probability distribution and packet loss probability for a given set of network, traffic and R-TWT parameters. Using this model, the access point can select the optimal R-TWT parameters for the given QoS requirements. The high accuracy of the model is proven by means of simulation.

Mobile communications and the accompanying demand for real-time services are growing rapidly. Dynamic resource allocation is required in technologies such as long-term evolution (LTE) and 5G to ensure fair and efficient resource usage. However, 3rd Generation Partnership Project (3GPP) does not impose a scheduling algorithm to assign those resources, leading to a vast body of downlink schedulers, each focusing on different aspects, such as throughput, packet loss ratio, energy efficiency etc. In this paper, we propose a new scheduler that aims to minimize delay violations, while maintaining a good throughput. The scheduler is based on a digital subscriber line (DSL) resource allocation mechanism, and uses the arrival rate together with the state of the flows and the network. We compare the scheduler to other schedulers from literature and observe that the proposed scheduler achieves a lower packet loss ratio (PLR) than the other schedulers, while maintaining a system high throughput.

In this paper we propose an analytical model for a general class of receiver-initiated MAC protocols for energy-harvesting wireless sensor networks. The aim is to evaluate the system occupancy of a sensor node and the average delay a packet in a node experiences, taking into account the energy that is consumed by the radio using the stored energy in a capacitor. Packets are generated by the node itself but may also arrive from neighbor nodes using a receiver-initiated MAC protocol. The radio switches between Transmit, Receive and Sleep states. During the Sleep state, energy is harvested and stored in a capacitor. The sensor node is modeled by means of a finite capacity queue with repeated server vacations of different types and the available energy is modeled by means of an extra variable. The system occupancy and the available energy are observed at inspection instants (i.e., the end of a service or the end of a vacation), resulting in a discrete-time Markov Chain. Closed form formulas for the system occupancy distribution at at arbitrary time instants together with the mean response time are derived. The model is applied to evaluate the sensor node’s performance for various parameter values.

The numerous applications of industrial automation have always posed many challenges for wireless connectivity. In the last decade, IEEE 802.15.4e time-slotted channel hopping (TSCH) networks have provided high reliability and low-power operation in such challenging industrial environments. Typically, TSCH networks employ one modulation at the physical layer and are thus limited by the characteristics of the chosen modulation in terms of, among others, data rate, reliability and energy efficiency. To tackle these limitations and to improve network performance and flexibility in those challenging industrial environments, this work explores the simultaneous use of multiple modulations in a TSCH network. Traditionally, TSCH relies on fixed-duration slots, large enough to send a packet of any size given the fixed data rate. In order to avoid wasting airtime when simultaneously using modulations with different data rates, we propose the concept of slot bonding. This allows the creation of different-sized bonded slots with a duration adapted to the data rate of each chosen modulation. To analyze the proposed slot bonding technique, we formally describe the TSCH slot bonding problem in terms of optimizing the packet delivery ratio while minimizing radio on time, with the inclusion of parent selection and interference avoidance. Afterward, we propose a genetic algorithm that allows us to implement the problem and find solutions heuristically. Finally, we provide insights into preferred parent selection and modulation configurations by using this heuristic approach during extensive simulation experimentation in which the scalability advantage of slot bonding over longer fixed-duration slots is also shown.

Billions of Internet-of-Things (IoT) devices are deployed worldwide and batteries are their main power source. However, these batteries are bulky, short lived, and full of hazardous chemicals that damage our environment. Relying on batteries is not a sustainable solution for future IoT. As an alternative, batteryless devices run on long-lived capacitors charged using energy harvesters. The small energy storage capacity of capacitors results in an intermittent on-off behavior. LoRaWAN is a popular low-power wide-area network technology used in many IoT devices and can be used in these new scenarios. In this work, we present a Markov model to characterize the performance of batteryless LoRaWAN devices for uplink and downlink (UL/DL) transmissions and we evaluate their performance in terms of parameters that define the model (i.e., device configuration, application behavior, and environmental conditions). Results show that LoRaWAN batteryless communications are feasible if choosing the proper configuration (i.e., capacitor size and turn-on voltage threshold) for different application behavior [i.e., transmission interval, UL/DL packet sizes (PSs)], and environmental conditions (i.e., energy harvesting rate). Since DL in the second reception window highly affects the performance, only small DL PSs should be considered for these devices. Besides, a 47-mF capacitor can support 1 B SF7 transmissions every 60 s at an energy harvesting rate of 1 mW. However, if no DL is expected, a 4.7-mF capacitor could support 1 B SF7 transmissions every 9 s.

Narrowband Internet of Things (NB-IoT) is becoming one of the most promising low-power wide area (LPWA) networking technologies. It can support more than 50 000 devices within a cell using licensed spectrum. NB-IoT provides low energy consumption, reliable connectivity and deep indoor coverage for the device, making it a good candidate for IoT use cases. NB-IoT introduces two novel energy-saving techniques, namely, extended discontinuous reception (eDRX) and power saving mode (PSM). This article presents a Markov chain model to evaluate the power consumption and latency of NB-IoT devices using PSM and eDRX. By exploiting the characteristics of the steady-state distribution of the Markov chain, the probabilities in steady-state can be obtained explicitly. Based on these probabilities, we calculate the system downlink (DL) latency as a function of different timers of these power-saving features. We also compare the model to simulation results obtained from the ns-3 event-based network simulator, to determine its accuracy. The results show that its performance in terms of energy and latency is comparable. Our model is accurate with consideration of the protocol details and the new radio resource control (RRC) Idle features of NB-IoT. The results show that the analytical model achieves an average accuracy of more than 91% for power consumption and DL latency. Lastly, we use the model to automatically determine the optimal parameter set in terms of latency and power consumption for various IoT use cases with different traffic requirements, based on multiobjective analysis of the Pareto front.

The MAC layer of the IEEE 802.11 standard deploys a CSMA/CA protocol to regulate the access to the shared medium. Not only other IEEE 802.11 stations but also non-IEEE 802.11 devices can be a source of interference, causing collisions and, therefore, re-transmissions, leading to an increased packet latency and a decrease of throughput. As in general, the non-IEEE 802.11 devices do not employ the IEEE8 802.11 CSMA/CA protocol (in particular carrier sensing and the behavior when the medium is sensed busy), the impact of the interference they cause may lead to vital performance degradation of the IEEE 802.11 network. This impact of non-IEEE 802.11 interfering sources on the network performance has not been accurately modeled yet in literature. In this paper, we first characterize a non-IEEE 802.11 interfering source by employing an on-off process. Then we propose, based on earlier results from Bianchi, an analytical model to predict latency and throughput in a saturated as well as an unsaturated network, considering that an interfering source is present. The model utilizes a Markov chain to correctly characterize the behavior of the back-off algorithm of a tagged station in the presence of an interfering source, as well as a Quasi Birth-Death (QBD) process to model the station’s packet queue behavior. We show that we can accurately estimate the impact of non-IEEE 802.11 inference on IEEE 802.11 performance. The model is validated through a comparison with measurements in a real IEEE 802.11 network as well as with an ns3-simulation, whereby a very good agreement is achieved (a difference less than 2%).

The static resource allocation which is usually assumed for the DSL physical layer leaves unused a significant portion of the achievable rate region. An alternative approach is to divide time into slots of short duration, and to change the resource allocation from each time slot to the next. A crosslayer scheduler then chooses a different resource allocation setting for each time slot by defining a utility function for each user n, and solving the corresponding network utility maximization (NUM) problem. For spectrum coordination, this NUM problem is non-convex and solving it is NP-Hard. This paper therefore introduces a fast algorithm, referred to as NUM-DSB, which converges to a local solution of the NUM problem. NUM-DSB can be applied to any NUM problem, regardless of the considered utility functions's characteristics. Simulation results show that NUM-DSB can compete with the state of the art algorithm for smooth non-convex network utility maximization.

The quality of experience of many modern network services depends on the delay performance of the underlying communications network. In DSL networks, crosstalk introduces competition for bandwidth among users. In such a competitive environment, delay performance is largely determined by the manner in which the cross-layer scheduler assigns bandwidth to the different users. Existing cross-layer schedulers optimize a simple metric, and do not consider important information that is contained within a queue's packets. In this paper, we present a new cross-layer scheduler, referred to as the minimal delay violation (MDV) scheduler, which optimizes a more elaborate metric that closely resembles the quality of experience of the users. Through simulations, it is shown that the new scheduler outperforms the state of the art in cross-layer scheduling algorithms.

Development and continuous operation of network management systems is a major challenge to future networks, where a large number of semi-independent devices jointly try to realize a working network. This work considers network testbed management, and more specifically on testbed management software for community networks. Because of the inherently unstructured and chaotic nature of community networks, managing components inside a community network with a frequently varying and unpredictable performance is particularly challenging. This paper focuses on the verification of community network testbed control software which has to cope with these challenges. We show how the application of a container-based unit testing approach has a positive impact on development efforts and testbed stability.

Community Wireless Networks are an emerging networking model, offering people the opportunity to build and manage their own network without being dependent on telecom operators. The strength of this type of networks lies in the involvement of the whole community, as each person benefitting from the community wireless network somehow contributes to the design, deployment and maintenance of the network. This model has resulted in large community wireless networks growing all over the world, connecting people in the local communities to each other and the Internet. Because of the rising popularity and demonstrated success, researchers are also becoming more interested in community networks. This paper presents guidelines and experiences from creating an outdoor testbed targeted at community wireless networks, based on experience and feedback from community network members.

In cellular networks, users that make frequent handovers and have a low time-of-stay in a cell (i.e., highly mobile users) might have a negative impact on the network performance. Furthermore the Quality of Service (QoS) experienced by these users might be low. This paper introduces a Self-Organising Network (SON) function, called the High Mobility SON function, that aims at reducing the amount of short stays in a multi-layer Long-Term Evolution (LTE) network. It does this by predicting the mobility behaviour of currently active users based on measurements, which were collected by users that were active in the past. Based on these predictions, the SON function aims at refraining from handovers to cells in which the user is likely to stay for a small amount of time, and at steering the user more appropriately. To assess the ability of the SON function to achieve its goals, simulations were performed in a scenario in which both macro and micro cells are deployed. Results show that the developed SON function is able to reduce the number of handovers by 17-23% and the number of short stays by as much as 43-49% at the cost of reducing the spectral efficiency by 13-15%.

A neighborhood discovery (ND), also referred to as a rendezvous (RDV), is a challenging and fundamental phase in opportunistic Cognitive Radio Networks (CRNs) due to changing network topology, the time and location varying spectrum availability and different channel qualities. Simplified solutions, such as, a central controller or common control channel are not feasible in opportunistic CRNs. Therefore, in order to be able to initiate a communication, there is a need of on-demand searching for a control traffic channel by cognitive radio (CR) users, usually working in an asynchronous manner. To meet these challenges we propose an asynchronous neighborhood discovery (AND) for opportunistic CRNs, which takes into account the asynchronous character of CRs, different channel ranks, as well as heterogeneous channel availability.

Community networks have emerged under the mottos of “break the strings that are limiting you”, “don't buy the network, be the network” or “a free net for everyone is possible”. Such networks create a measurable social impact as they provide to the community the right and opportunity of communication. As any other network that mixes wired and wireless links, the routing protocol must face several challenges that arise from the unreliable nature of the wireless medium. Link quality tracking helps the routing layer to select links that maximize the delivery rate and minimize traffic congestion. Moreover, link quality prediction has proved to be a technique that surpasses link quality tracking by foreseeing which links are more likely to change its quality. In this work, we focus on link quality prediction by means of a time series analysis. We apply this prediction technique in the routing layer of large-scale, distributed and decentralized networks. We demonstrate that this type of prediction achieves about a success probability of about 98% in both the short and long term.

The population of elderly people is increasing rapidly, which becomes a predominant aspect of our society. For several reasons so significant a share of the human society is simply regarded as "retired" -- a word condemning the elderly to a reduced participation in all active life, regardless of their actual conditions and abilities. In previous work, we discussed how community resources can be organized in a better way. In particular we introduced a so-called mutual assistance community -- a digital ecosystem that removes any predefined and artificial distinction between care-givers and care-takers and provides a service-oriented infrastructure for intelligent matching of the supply and demand of services. According to this new paradigm all people are potentially active participants to activities defined by the people's current needs, abilities, locations, and availabilities. Moving from this conceptual view to practical implementation calls for an architecture able to match adequately demand and supply of services. This paper presents an implementation of such an architecture based on semantic service description and matching. In comparison with our previous implementation, main added values include a greater flexibility in service representation and service matching and considerable improvements in performance.

Contemporary Wireless Sensor Networks like Smart Offices and Smart Cities are evolving to become multi-purpose application hosting platforms. These WSN platforms can simultaneously support multiple applications which may be managed by multiple actors. Reconfigurable component models have been shown to be viable solutions to reducing the complexity of managing and developing these applications while promoting software re-use. However, implicit parameter dependencies between components make reconfiguration complex and error-prone. Our approach achieves automatic composition-safe re-parametrization of distributed component compositions. To achieve this, we propose the use of language annotations that allow component developers to make these dependencies explicit and constraint-aware network protocols to ensure constraint propagation and enforcement.

Due to the changing network topology and the time and location varying spectrum availability in Cognitive Radio Networks (CRNs), there is a need of on-demand searching for a control traffic channel by CR users in order to be able to initiate a communication. This neighborhood discovery phase, also referred to as a rendezvous (RDV) phase, is challenging due to the dynamics of CRNs. There are a number of different proposed solutions (pseudo-random or systematic approaches such as quorum systems) to tackle this issue, however, not so many elaborate on the asynchronous character of CRNs, and even less taking into account channel heterogeneity in terms of quality. In this study, on the one hand, we propose a novel quorum system-based neighborhood discovery protocol, which operates on channels having different priorities, on the other hand, we perform an analysis of the effect of asynchronism on the proposed protocol. We analyze the behavior of the protocol in terms of rendezvous opportunities, time-to-rendezvous, and the measured error margins for both, for different asynchronous offsets. We show that an asynchronism can bring noticeable profits over the slot synchronized case.

There is a variety of community networks out there. In this paper we try to shed a light on the community network landscape by presenting the results of a questionnaire filled in by different community network organisations around the world. We demonstrate the variety of infrastructure used and the different management approaches of the network within those communities. We also show the common challenges of the communities and provide pointers to tackle those challenges.

Due to the extreme energy requirements often found in sensor networks and the fact that these sensor networks are being used for an increasingly wide variety of applications, there currently exist many different sensor network MAC protocols each optimised for a different set of application requirements. Since these MAC protocols are not compatible with each other, there is generally no interoperability between sensor networks. This lack of interoperability becomes a severe problem when connectivity between sensor networks is required. In this paper, we demonstrate the feasibility of using Virtual Gateways, sensor nodes running multiple MAC protocols simultaneously on top of a single radio interface, to enable connectivity between sensor networks. To this end we have developed MultiMAC, a network stack for TinyOS capable of running multiple MAC protocols at the same time. We show that the architecture of the MultiMAC stack is flexible and extensible enough to support a wide variety of MAC protocols and that the overhead of this network stack is minimal.

We present a family of gossiping algorithms whose members share the same structure though they vary their performance in function of a combinatorial parameter. We show that such parameter may be considered as a "knob" controlling the amount of communication parallelism characterizing the algorithms. After this we introduce procedures to operate the knob and choose parameters matching the amount of communication channels currently provided by the available communication system(s). In so doing we provide a robust mechanism to tune the production of requests for communication after the current operational conditions of the consumers of such requests. This can be used to achieve high performance and programmatic avoidance of undesirable events such as message collisions.

We developed a network platform that is responsible for an uninterrupted and seamless connectivity from the train to the wayside through heterogeneous wireless access technologies. However, limiting the offered services to only an onboard Internet is not a feasible business case. A viable one should extend to a broad spectrum of railway communication services like: train control, diagnostics, real time passenger information, entertainment, security CCTV surveillance etc. In a highly dynamic environment (from the communication link point of view) such a fast moving train, it is necessary to introduce prioritization among different traffic classes. This will implicitly determine under what conditions a certain flow should get suspended or dropped in order to preserve the flows of a higher priority as long as possible and to ensure that they meet their QoS demands. The first step towards this goal is data traffic differentiation.

As community networks are being deployed more often, interest in using them as testbeds is growing too. Frameworks like the cOntrol and Management Framework (OMF) are helpful software tools to organize, control and instrument the testbeds deployed on those networks. However, community networks have a very heterogeneous infrastructure in which less powerful, embedded devices will play an important role due to their low cost. This work will analyze the overhead generated by the OMF framework when deployed on embedded devices. Possible performance hits introduced by the overhead on both desktop and embedded systems will be presented and compared.

The growing popularity of sensor networks has resulted in the creation of various MAC protocols, each optimized for a different set of application requirements. However, all of these heterogeneous MAC protocols are designed under the assumption that all nodes in the wireless environment use a common MAC protocol. When multiple sensor networks are deployed in the same wireless environment, this assumption no longer holds since different sensor networks will most likely make use of different MAC protocols. This paper investigates the effect of interference between sensor networks using heterogeneous MAC protocols, based on the network performance of these sensor networks. The network performance of TDMA, CSMA/CA, T-MAC and LPL-MAC, a variant of B-MAC, is examined. Test results show that depending on the interfering MAC protocol, the amount of interference and the load of the network, the average energy consumption can increase by 17% for contention-based protocols and 62% for TDMA based protocols. Moreover this interference can cause the end-to-end data loss to more than double for contention-based protocols while for TDMA protocols the end-to-end data loss can increase from 0.1% to more than 40%.

Body Sensor Networks (BSNs) form a promising technology to supply healthcare to an ageing population. A large number of sensor devices, radios and MAC protocols are being developed. However, current solutions all assume a single-hop topology, while research results confirm the need for multi-hop topologies. In these multi-hop networks, because of the small scale of a BSN, node mobility will arise frequently. This work presents the first algorithm to support such Mobile BSNs, while remaining energy efficient.

Wireless body area networks (WBANs) offer many promising new applications in the area of remote health monitoring. An important element in the development of a WBAN is the characterization of the physical layer of the network, including an estimation of the delay spread and the path loss between two nodes on the body. This paper discusses the propagation channel between two half-wavelength dipoles at 2.45 GHz, placed near a human body and presents an application for cross-layer design in order to optimize the energy consumption of different topologies. Propagation measurements are performed on real humans in a multipath environment, considering different parts of the body separately. In addition, path loss has been numerically investigated with an anatomically correct model of the human body in free space using a 3-D electromagnetic solver. Path loss parameters and time-domain channel characteristics are extracted from the measurement and simulation data. A semi-empirical path loss model is presented for an antenna height above the body of 5 mm and antenna separations from 5 cm up to 40 cm. A time-domain analysis is performed and models are presented for the mean excess delay and the delay spread. As a cross-layer application, the proposed path loss models are used to evaluate the energy efficiency of single-hop and multihop network topologies.

This paper introduces a tool that allows designers to make use of adaptively redundant data structures with commodity programming languages such as C or Java. Designers using such tool can define redundant data structures in which the degree of redundancy is not fixed once and for all at design time, but rather it changes dynamically with respect to the disturbances experienced during the run time. Our approach attunes the degree of redundancy required to ensure data integrity to the actual faults being experienced by the system and provides an example of adaptive fault-tolerant software. We prove the effectiveness of our tool by showing that adaptive replication reaches the same effectiveness of static replication but consuming much less resources and computing time.

In this paper we present a cross layer topology preserving channel selection protocol for a two interface wireless mesh network. The presented protocol is a cluster driven channel selection protocol, preserving a single interface to maintain connectivity and using the other interface to participate in small clusters. The clusters are organized by an independent set clustering algorithm, in which the cluster head dictates the operating channel for the local cluster. We show that the channel selection algorithm doubles the capacity for both a regular grid and a random topology.

Elder people are becoming a predominant aspect of our societies. As such, solutions both efficacious and cost-effective need to be sought. This paper proposes a design to construct a virtual ambient assisted living community where dwellers make contributions to the community so as to best utilize resources and minimize costs. We use service oriented architecture (SOA) to orchestrate the available resources inside the community, thus bringing social intelligence to the social computing. We also propose building such a virtual community making use of virtual reality and in the form of serious game [Stuart Rory, 1996]. Daily activities and instruments (such as sensors, cameras, etc.) in real-life may be translated into their virtual community equivalents, and activities happening in the virtual world will trigger corresponding actions in the real world, so that inter-reality may be obtained through this virtual community. We expect such a virtual community could help not only efficiently utilizing the social resources in maintaining the independent living of the elderly people, but also helping these people maintain their connections to the society and bring them entertainment, so that the quality of their living standard may be improved at the same time.

Elder people are becoming a predominant aspect of our societies. As such, solutions both efficacious and cost-effective need to be sought. The approach pursued so far to solve this problem used to increase the number of people working in the health sector, e.g. doctors, nurses, etc. This increases the costs, which is becoming a big burden for countries. In this paper we propose a new concept in the health management of elder people, which we name as "participant". We propose the "participant" concept to encourage elder people to participate in those group activities that they are able to. Their roles in these activities are not passively requesting help, but actively participating to some healthcare processes. Characteristics of the participant approach are that medical resources are efficiently spared with this model, and the social network of the elder people is kept. A "virtual community" for mutual assistance is set up in this paper, and the simulations demonstrate that the "participant" model could fully utilize the community resources. Furthermore, the psychological health of the elder people will be improved.

In this paper we present a protocol performing on demand distributed channel selection in multi channel, multi interface wireless mesh networks, based on the exchange of control messages. The link based channel reservation happens almost instantly when data traffic is sent through the network, and does not require long-term traffic profiles or measurements. The protocol is both simulated and implemented using the IEEE 802.11 b/g protocol. We show that in a raster topology, the protocol successfully optimizes the local spectrum usage at 87% of the nodes, and that globally, an equal amount of links is allocated to each of the channels used for the transport of data packets.

In this paper we present a new theoretical model to assess the performance of a class of batch scheduling orders in a forward DVB-S2 satellite link. The scheduling order in a DVB-S2 link will determine the order in which IP packets are transmitted to the receivers and thus determines the amount of required padding and sub-optimal transmissions. The validity of the model is investigated by various simulation runs which show a very close agreement with the theoretical model. Using this model we also identify the optimal scheduling order within this class of orders, given that some mild and realistic conditions on the modulation and coding schemes apply.

One of the major advantages of wireless communication over wired is the flexibility when creating links between nodes. But this comes at a price as influences from outside the mesh network can distort communication between the nodes and even the nodes themselves interfere with each other. By carefully selecting channels where each link transmits data on, the interference can be minimized causing the throughput and end-to-end delay to be improved. We propose an algorithm that only uses locally distributed information to find the best channel selection for each link. The algorithm is independent of the used routing algorithm and scales well. Using simulations we will demonstrate scalability, convergence and finding an optimal solution.

Vehicular communication is gaining more and more interest from big consortia and companies in the car industry. Wireless communication in a vehicular environment creates unique opportunities but poses also its own challenges. Therefore we proposed in previous work a new routing protocol, REACT, which uses geographical information and is able to react to a fast changing environment. In this paper, we will look at a few optimizations for this protocol in order to make it more adaptive to the current network conditions. As vehicles move very fast, link breaks occur more often. We attempt to predict this behavior, trying to use a link as long as possible but not longer than it really exists. Another important part of the REACT protocol consists of beaconing as means of exchanging position information with neighbors. The interval between two consecutive beacons is an important parameter in determining the end-to-end delay and we propose an algorithm that adapts this parameter in order to speed up neighbor discovery without generating too much beaconing overhead. The two optimizations were implemented and tested in a simulator and the results show a performance amelioration in the end-to-end delay in scenarios with sparse and dense road traffic.

Wireless body area networks (WBANs) form a new and interesting area in the world of remote health monitoring. An important concern in such networks is the communication between the sensors. This communication needs to be energy efficient and highly reliable while keeping delays low. Mobility also has to be supported as the nodes are positioned on different parts of the body that move with regard to each other. In this paper, we present a new cross-layer communication protocol for WBANs: CICADA or Cascading Information retrieval by Controlling Access with Distributed slot Assignment. The protocol sets up a network tree in a distributed manner. This tree structure is subsequently used to guarantee collision free access to the medium and to route data towards the sink. The paper analyzes CICADA and shows simulation results. The protocol offers low delay and good resilience to mobility. The energy usage is low as the nodes can sleep in slots where they are not transmitting or receiving.

Failure detection protocols an important building block of fault-tolerant distributed systems-are often described by their authors making use of informal pseudocodes of their own devising. Often these pseudo-codes use syntactical constructs that are not available in COTS programming languages such as C or C++. This translates into informal descriptions that require ad hoc interpretations and implementations. Being informal, these descriptions cannot be tested by their authors, which may translate into insufficiently detailed or even faulty specifications. Being non-standard, they require the reader to understand each time a different lingo. This paper tackles the above problem introducing a formal syntax for the expression of failure detection protocols and a C library that implements that syntax: a toolset to express and reason about failure detection protocols. The resulting specifications are more diffuse but non ambiguous and eligible for becoming a standard form among researchers and practitioners.

We propose the "bounds selection-dynamic reset algorithm" (sB-DRA) protocol for wireless ad hoc LANs. The sB-DRA consists of the selection/adjustment of the contention window (CW) interval (selection Bounds algorithm-sB from our previous work (Romaszko and Blondia, 2006)) and the resetting of the contention window value dynamically after a dropped packet or successful transmission (enhanced dynamic resetting algorithm - DRA). The sB algorithm allows to adjust the lower and upper bounds of the CW interval taking into account the number of 1-hop active neighbours and the number of transmission attempts during the recovery mechanism. The DRA considers the number of 1-hop neighbours and their change (fast/slow increase/decrease) during recovery process. The enhanced DRA algorithm can be tuned dynamically depending on the channel conditions. The sB-DRA protocol achieves better throughput and significantly reduces the number of collisions and packet loss compared to the IEEE 802.11 DCF standard (1999). We have also shown that the sB algorithm outperforms the basic (without resetting the Backoff ranges mechanism) "deterministic contention window algorithm" (DCWA) (Ksentini et al., 2005) in mobile ad hoc networks.

The so-called wireless revolution is producing new services based on the concept of mobile computing. We remark how mobile computing technologies call for effective software engineering techniques to design, develop and maintain mobile services, i.e., services that are prepared to continue the distribution of a fixed, agreed-upon quality of service despite of the changes in the location of the client software and the characteristics of the environment. Hence novel paradigms are required for software engineering so as to provide effective system structures for mobile services while keeping the design complexity under control. In this paper we discuss the problem and propose one such structure.

Elder people are becoming a predominant aspect of our societies and solutions both efficacious and cost-effective need to be sought. This paper proposes a service-oriented infrastructure approach to this problem. We propose an open and integrated service infrastructure to orchestrate the available resources (smart devices, professional carers, informal carers) to help elder or disabled people. Main characteristic of our design is the explicitly support of dynamically available service providers such as informal carers. By modeling the service description as Semantic Web Services, the service request can automatically be discovered, reasoned about and mapped onto the pool of heterogeneous service providers. We expect our approach to be able to efficiently utilize the available service resources, enrich the service options, and best match the requirements of the requesters.

In this paper we study the influence the DCCP transport protocol has on the end-user quality of video applications. We consider an application that aims to provide a video of constant quality to the user and introduce a model for such a source. The end-user quality of the application is evaluated in a variety of simulation scenarios

Wireless body area networks (WBANs) have gained a lot of interest in the world of medical monitoring. Current implementations generally use a large single hop network to connect all sensors to a personal server. However recent research pointed out that multihop networks are more energy-efficient and even necessary when applied near the human body with inherent severe propagation loss. In this paper we present a slotted multihop approach to medium access control and routing in wireless body area networks, the wireless autonomous spanning tree protocol or WASP. It uses crosslayer techniques to achieve efficient distributed coordination of the separated wireless links. Traffic in the network is controlled by setting up a spanning tree and by broadcasting scheme messages over it that are used both by the parent and the children of each node in the tree. We analyze the performance of WASP and show the simulation results

The IEEE DCF 802.11, currently used as wireless local area networking standard, wastes bandwidth capacity and energy resources due to many collisions. To attenuate these problems we propose a neighbour and energy aware contention avoidance MAC protocol (NEWCAMac). The NEWCAMac protocol defines novel algorithms to estimate a minimum and maximum contention window size taking into account the number of neighbours in the one-hop neighbourhood and the energy level of the battery. It also exploits a new backoff algorithm based on the number of currently active neighbours and the probability of successful transmission. Our novel protocol achieves better throughput and noticeably reduces the number of collisions resulting in longer network lifetime as compared with the IEEE 802.11 DCF standard

This paper presents an analysis of several neighbor sensing approaches for the OLSR routing protocol. While several performance studies of OLSR proceed this work, few attention has been paid to the impact of neighbor sensing on the performance of ad hoc routing protocols. The goal of this article is to better understand how neighbor sensing can contribute to packet loss in an OLSR network and thus degrade the overall performance. Three neighbor sensing schemes are compared: the OLSR HELLO messaging protocol, Fast-OLSR and a link-layer feedback scheme that uses information of the 802.11 MAC to determine lost links. To allow more detailed analysis of the events occuring in the network we initially limit our simulation setup to a simple scenario. As a result we are able to seperate the loss of packets into loss due to the neighbor sensing mechanism used and loss due to the impact of neighbor sensing on the other protocol operations. In the second part of this paper we compare the performance of the link-layer feedback scheme to OLSR in a random waypoint scenario.

A system structure for adaptive mobile applications is introduced and discussed, together with a compliant architecture, and a prototypic implementation. A methodology is also introduced, which exploits our structure to decompose the behavior of non-stable systems into a set of quasi-stable scenarios. Within each of these scenarios, we can exploit the knowledge of the available QoS figures to express simpler and better adaptation strategies.

We present a detailed analysis of the maximum channel utilization and loss performance in an optical buffer having access to a single outgoing channel. Such a system, consisting of a number of fiber delay lines, can only realize a discrete set of delays to resolve output port contention. This leads to an underutilization of the channel capacity, which reduces overall performance. The framework considered in this paper greatly simplifies the assumptions made in previous work, which allows us to study the impact of a variety of new parameters on the performance, e.g., the burstiness of the arrival process and the correlation of consecutive burst lengths. Moreover, we present exact results for both the channel utilization and loss rate in such a system using matrix analytic methods. We show that carefully choosing the granularity parameter can, in some cases, make a substantial difference when trying to realize lower buffer losses or a high channel utilization. Optimal values of the granularity parameter are shown to be closely related to the optical burst length distribution.

In this paper, we evaluate a low latency handoff protocol for MIPv4, the post-registration handoff method. This mechanism proposed by the IETF tries to improve the performance of hierarchical mobile IP by decreasing the handoff latency. We give a detailed description of the protocol behavior by means of an ns simulation and propose a simple queuing model to study the influence of various parameters on the protocol performance.

A statistical multiplexer is a basic model used in the design and the dimensioning of communication networks. The multiplexer model consists of a single server queue with constant service time and a more or less complicated arrival process. The aim is to determine the packet loss probability as a function of the capacity of the buffer. In this paper, we show how rational approximation techniques may be applied to compute the packet loss efficiently. The approach is based on the knowledge of a limited number of sample values, together with the decay rate of the probability distribution function. A strategy is proposed where the sample points are chosen automatically. The accuracy of the approach is validated by comparison with both analytical results obtained using a matrix-analytic method and simulation results.

Mobile IP allows node mobility involving changes of point-of-attachment to the Internet. In order to reduce the impact on the performance and the signaling overhead, hierarchical mobility management schemes have been introduced. These schemes define protocols that allow movements within a domain to be handled locally, without involvement of the mobile node's home network. In order to reduce more the packet losses during handoff, new schemes have been defined, such as smooth handoff. By storing packets temporarily in the access point after the mobile host has left and forwarding them to the new access point as soon as the mobile has connected to it, it is possible to reduce significantly the packet loss. In this paper we develop an analytical model and a simulation program using OPNET Modeler to evaluate the packet loss and packet delay for UDP streams and the throughput for TCP streams that are involved in a handoff. We show that, in spite of the buffering capabilities of the previous access point, packets may still get lost. The reason for this loss is identified and solutions to this problem are proposed.

A dynamic MAC (Medium Access Control) protocol demonstrator for ATM PON (Passive Optical Network) was realised and tested. The prototype is based on a SuperPON transport system, which allows implementing downstream grants per ONT (Optical Network Termination) or subdivided per T-Cont class (Traffic Container) and upstream requests by piggybacking or dedicated polling slots. The demonstrator platform was made configurable in order to evaluate dynamic bandwidth allocation schemes for SuperPON and for G.983.dba APON.

This paper considers the selective drop (SD) algorithm, a packet aware buffer acceptance algorithm used with the unspecified bit rate ATM service category. The influence of the parameters of the SD algorithm on the transient performance results (efficiency and fairness) is studied when starting from an unfair start situation. This is done using an analytical model where two responsive sources send their traffic in packets consisting of cells via a buffer on which the SD algorithm is implemented. Three different scheduling algorithms are used in combination with the SD algorithm. Based on an extensive set of numerical examples, observations are made. From these results, one of the most important conclusions is that a large improvement of the fairness results is seen when SD is implemented, irrespective of the exact setting of its parameters. On the efficiency results, these parameters have however a more important effect. So it is recommended to implement SD to increase the fairness, but with a parameter setting focussed on the efficiency results.

A contention resolution scheme for an uplink contention channel in a wireless access network is presented. The scheme consists of a tree algorithm, namely the identifier splitting algorithm (ISA), combined with a polling scheme. Initially, ISA is used, but at a certain level of the tree, the scheme switches to polling of the stations. This scheme is further enhanced by skipping a few levels in the tree when starting the algorithm (both in a static and a dynamic way) and by allowing multiple instants simultaneously. An analytical model of the system and its variants leads to the evaluation of its performance, by means of the delay density function and the throughput characteristics. This model is used to investigate the influence of the packet arrival rate, the instant at which the ISA scheme switches to polling, the starting level of the ISA scheme, and the use of multiple instances on the mean delay, the delay quantiles, and the throughput.

In this paper we derive an expression for the asymptotics of the buffer length distribution of a discrete-time infinite capacity single server queue with deterministic service time and its input process belonging to a class of long range dependent discrete-time M/G//spl infin/ processes. This class of arrival process is defined as follows. At each time slot sequences of back-to back customers are generated according to a Poisson distribution with parameter X. The length of such a sequence is assumed to asymptotically behave like a Pareto distribution with parameter s, i.e. the probability that a sequence consists of k customers is given by ck/sup -3/ for k/spl rarr//spl infin/, with c>0 and 2<s<3. Due to the heavy tail of the members of this class of distributions, the presented class of M/G//spl infin/ processes has the long range dependence property (i.e., the autocorrelation function decays as a power of the lag time). We show that in this case the asymptotic behavior of the tail probabilities of the stationary distribution of the buffer occupancy is given by (/spl lambda/cp/sup s-2//(s-2)(s-1)(1-/spl rho/))n/sup 2-s/ for n/spl rarr//spl infin/, with /spl rho/ representing the load of the system. This result is obtained using a generating function approach and the Tauberian theorem for a power series. Furthermore, an application towards traffic management and simulation results are presented.

This paper determines packet level performance measures of a MAC protocol for a wireless ATM local area network. A key characteristic of the MAC protocol is the identifier splitting algorithm with polling, a contention resolution scheme used to inform the base station about the bandwidth needs of a mobile station when no piggybacking can be used. We consider higher layer packets that are generated at the mobile station and investigate the influence of the traffic characteristics of the packet arrival process on the efficiency of the protocol and on the delay that packets experience to access the shared medium.

The paper addresses the way in which information transfer can be achieved in broadband indoor radio LANs using the asynchronous transfer mode (ATM). A multi-access protocol for ATM-based access is described which uses a request/permit mechanism to control access to the shared medium. This protocol approximates a global FIFO strategy. It has been defined for a passive optical network in the RACE project R2024 Broadband Access Facilities, and is currently being implemented in the demonstrator of this project.

The authors propose a versatile point process as a model for a large class of variable bit rate sources and their superpositions. The process belongs to the class of discrete-time batch Markovian arrival processes. Its use leads to computationally tractable and accurate solutions for the following performance measures of the related statistical multiplexer: buffer occupancy distribution, cell loss probability, and conditional cell loss probability. It is shown that the output process of the multiplexer belongs to the same class of processes.>