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In this paper, we present a comprehensive algorithmic framework for discrete-time flow-level simulation of data networks. We first provide a simple algorithm based upon iterative equations useful for the simulation of networks with static traffic demands, and we show how to determine packet loss and throughput rates using a simple example network. We then extend these basic equations to a simulation method capable of handling queue and link delays in dynamic traffic scenarios and compare results from flow-level simulation to those obtained by packet-level simulation. Finally, we illustrate the tradeoff between computational complexity and simulation accuracy which is controlled by the duration of a single iteration interval Δ. [ABSTRACT FROM AUTHOR]

The paper proposes a new method to calculate the occupancy distribution and the blocking probability in the full-availability group with multi-rate traffic and bandwidth reservation. In the presented method, the occupancy distribution in a group is calculated with the application of the proposed asymmetric convolution operation that takes into consideration the influence of the reservation mechanism upon the probability of passing between the states. The results of the analytical calculations of the blocking probability in the system with bandwidth reservation obtained on the basis of the proposed analytical method are compared to the data obtained on the basis of other known analytical methods and to the results of the simulation. [ABSTRACT FROM AUTHOR]

To support battery powered mobile broadband wireless access devices efficiently, IEEE 802.16e defines a sleep mode operation for conserving the power of mobile terminals. In this paper we propose a theoretical Phase-type (PH) based Markov chain model to analyze the performance of IEEE 802.16e sleep mode operation. The model describes the behavior of the mobile stations working in sleep mode. In particular, the service process is designed as a discrete PH model. By means of the mathematic tools of PH theory we then derive the closed-form expressions of the mean sojourn time of packets and power consumption. Comparison with simulation results shows that the model provides an accurate prediction of the system performance. Furthermore, we propose a simple utility function to quantify the efficiency of sleep mode operation which takes the joint effect of sojourn time and power saving into account. This function allows mobile stations to decide when to enable sleep mode operation for power saving. [ABSTRACT FROM AUTHOR]

Traffic matrices constitute essential inputs in a wide variety of network planning and management functions as they provide the traffic volumes that flow between the node pairs in a network. In operational IP networks, it is desirable that traffic matrix (TM) estimation relies on information that is directly obtainable from SNMP system measurements i.e., link counts data. Existing approaches for TM estimation based on link counts have been shown to have limited accuracy and cannot be generally applied to practical IP networks. In this paper, we propose a new method for TM estimation which makes more accurate assumptions about the traffic characteristics of the flows between node pairs and, specifically, a Markovian Arrival Process of order two (MAP-2) has been applied for this purpose. The presented evaluation study shows the ability of the method to accurately capture the correlation and burstiness statistics of real IP flows and, therefore, can be successfully applied in IP network management functions. [ABSTRACT FROM AUTHOR]

This paper considers the packet recovery performance of forward error correction (FEC) for a single-server queueing system with a finite buffer fed by two independent input processes; one is a general renewal input process in which the interarrival times of packets are independent and identically distributed according to a general distribution, and the other is a Poisson arrival process. We analyze the packet- and block-level loss probabilities, and investigate the recovery performance of FEC at block level. Numerical examples show that the block-loss probability is significantly improved by FEC when the system can only accommodate a small number of packets. It is also shown that FEC recovery is more effective than packet buffering when the traffic intensity is large. [ABSTRACT FROM AUTHOR]

The prevalent mechanism to avoid congestion in IP networks is the control of the sending rate with TCP. Dynamic routing strategies at the IP layer are not deployed because of problems like route oscillations and out-of-order packet deliveries. With the adoption of P2P technology, routing is done also in these overlay networks. With multi-source download protocols peers upload and download to/from other peers in parallel. Based on congestion pricing for IP networks this paper proposes a rate control algorithm for P2P over IP networks. A peer adopts the functionality of TCP and extends the congestion window mechanism with information from the overlay network. Thus, a sending peer is able to shift traffic from a congested route to an uncongested one. This change in the rate allocation will be balanced by other peers in the overlay. Hence, the receiving peers experience no degradation of their total download rate. [ABSTRACT FROM AUTHOR]

We consider an asymmetric cyclic polling system with general service-time and switch-over time distributions with so-called two-stage gated service at each queue, an interleaving scheme that aims to enforce fairness among the different customer classes. For this model, we (1) obtain a pseudo-conservation law, (2) describe how the mean delay at each of the queues can be obtained recursively via the so-called Descendant Set Approach, and (3) present a closed-form expression for the expected delay at each of the queues when the load tends to unity (under proper heavy-traffic scalings), which is the main result of this paper. The results are strikingly simple and provide new insights into the behavior of two-stage polling systems, including several insensitivity properties of the asymptotic expected delay with respect to the system parameters. Moreover, the results provide insight in the delay-performance of two-stage gated polling compared to the classical one-stage gated service policies. The results show that the two-stage gated service policy indeed leads to better fairness compared to one-stage gated service, at the expense of a decrease in efficiency. Finally, the results also suggest simple and fast approximations for the expected delay in stable polling systems. Numerical experiments demonstrate that the approximations are highly accurate for moderately and heavily loaded systems. [ABSTRACT FROM AUTHOR]

We investigate the end-to-end delay bounds in large scale networks with Differentiated services (DiffServ) architecture. It has been generally believed that networks with DiffServ architectures can guarantee the end-to-end delay for packets of the highest priority class, only in lightly utilized cases. We focus on tree networks with DiffServ architecture and obtain a closed formula for delay bounds for such networks. We further show that, in tree networks with DiffServ architecture, the delay bounds for highest priority packets exist regardless of the level of network utilization. These bounds are quadratically proportional to the maximum hop counts in heavily utilized networks; and are linearly proportional to the maximum hop counts in lightly utilized networks. We argue that based on these delay bounds DiffServ architecture is able to support real time applications even for a large tree network. Considering that tree networks, especially the Ethernet networks, are being adopted more than ever for access networks and for provider networks as well, this conclusion is quite encouraging for real-time applications. Throughout the paper we use Latency-Rate ($\mathcal{LR}$) server model, with which it has been proved that First In First Out (FIFO) and Strict Priority schedulers are $\mathcal{LR}$ servers to each flows in certain conditions. [ABSTRACT FROM AUTHOR]

This paper presents a simple approximation to the delay distributions commonly used in traffic engineering and network planning. A key advantage of the approximation is its ability to estimate end-to-end delay without requiring convolutions or Laplace transforms. Two example applications to network planning are given: first, directly to the estimation of percentiles of end-to-end delay from component subnetwork measurements, and second, to network element characterization for computing delays in signaling or other systems that exhibit complex multiple message exchanges. A consideration of the accuracy of the method is included for both examples. [ABSTRACT FROM AUTHOR]

In this paper we present a method for determining optimal routes along selected paths in a wireless mesh network based on an interference aware delay analysis. We develop an analytic model that enables us to obtain closed form expressions for delay in terms of multipath routing variables. A flow deviation algorithm is used to derive the optimal flow over a given set of routes. The model takes into account the effects of neighbor interference and hidden terminals, and tools are provided to make it feasible for the performance analysis and optimization of large-scale networks. Numerical results are presented for different network topologies and compared with simulation studies. [ABSTRACT FROM AUTHOR]

In this paper we study load balancing in wireless mesh networks when the MAC layer of the network is modelled by STDMA. We formulate the linear problem for joint optimization of traffic allocation and transmission schedule. Both unconstrained path set, allowing arbitrary routing, and predefined paths are considered. In our numerical examples roughly third of the load of the most congested link can be reduced by load balancing. This reduction in the load decreases the delays of the network as well as increases the reliability of the system if link conditions change suddenly. [ABSTRACT FROM AUTHOR]

In this paper we aim to develop an analytical model of the cross-layer characteristics of a Near End Cross Talk (NEXT) limited ADSL channel and determine the effective channel capacity of such a system. The ADSL users often encounter impact of other users in the same cable system due to NEXT interference that reduces the transmission capacity of the ADSL link. At the same time, due to application behavior, the source traffic of the user introduces a level of uncertainty. This paper proposes a model for capturing the cross-layer dynamics of these two uncertainties of an ADSL system. The model provides a closed form analytical method for determining the effective capacity of the ADSL system limited by NEXT interference. [ABSTRACT FROM AUTHOR]

Given a placement of wireless nodes in space and a traffic demand between pairs of nodes, can these traffic demands be supported by the resulting network? A key issue for answering this question is wireless interference between neighbouring nodes including self interference along multi-hop paths. This paper presents a generic model for sustainable network load in a multi-hop wireless network under interference constraints, and recasts this model into a multicommodity flow problem with interference constraints. Using Farkas' Lemma, we obtain a necessary and sufficient condition for feasibility of this multicommodity flow problem, leading to a tight upper bound on network throughput. Our results are illustrated by examples. [ABSTRACT FROM AUTHOR]

In future Internet, multi-network services correspond to a new paradigm that intelligence in network control is gradually moved to the edge of the network. As a consequence, the application itself can influence or determine the amount of consumed bandwidth. Thus the user behaviour may change dramatically. This impacts the Quality of Service (QoS) and the Quality of Experience (QoE), a subjective measure from the user perspective of the overall value of the provided service or application. A selfish user or application tries to maximize its own QoE rather than to optimize the network QoS, in contrast to a legacy altruistic user. In this paper we present the IQX hypothesis which assumes an exponential functional relationship between QoE and QoS. This contribution is a first step towards the quantification of the QoE for edge-based applications, where an example of VoIP is taken into account. Starting from a measurement of the Skype application, we show the basic properties of selfish and altruistic user behaviour in accordance to edge-based intelligence. The QoE is quantified in terms of MOS in dependence of the packet loss of the end-to-end connection, whereby Skype's iLBC voice codec is used exemplarily. It is shown that the IQX hypothesis is verified in this application scenario. Furthermore, selfish user behaviour with replicated sending of voice datagrams is investigated with respect to the obtained QoE of a single user. In addition, the impact of this user behaviour on congestion in the network is outlined by means of simulations. [ABSTRACT FROM AUTHOR]

Cross-layer design has been proposed to optimize the performance of networks by exploiting the inter-relation among parameters and procedures at different levels of the protocol stack. This may be particularly beneficial in wireless scenarios, and for quality-of-service support. This paper proposes a quantitative study of cross-layer performance optimization for Voice over WiFi communications, which enables design engineers to analyze and quantify inter-layer dependencies and to identify the optimal operating point of the system, by using cost-benefit principles. Furthermore, insight gained on the problem enables the proposal of design principles for a Call Admission Control scheme able to enhance the overall system performance by limiting the number of users in the system and signalling to the active terminals of the proper parameter settings to optimize overall performance. [ABSTRACT FROM AUTHOR]

This paper develops a new state-space model for long-range dependent (LRD) teletraffic. A key advantage of the state-space approach is that forecasts can be performed on-line via the Kalman predictor. The new model is a finite-dimensional (i. e., truncated) state-space representation of the FARIMA (fractional autoregressive integrated moving average) process. Furthermore, we investigate, via simulations, the multistep ahead forecasts obtained from the new model and compare them with those achieved by fitting high-order autoregressive (AR) models. [ABSTRACT FROM AUTHOR]

Wireless ad-hoc networks are based on shared medium technology where the nodes arrange access to the medium in a distributed way independent of their current traffic demand. This has the inherent drawback that a node that serves as a relay node for transmissions of multiple neighboring nodes is prone to become a performance "bottleneck". In the present paper such a bottleneck node is modeled via an idealized fluid-flow queueing model in which the complex packet-level behavior (mac) is represented by a small set of parameters. We extensively validate the model by ad-hoc network simulations that include all the details of the widely used ieee 802.11 mac-protocol. Further we show that the overall flow transfer time of a multi-hop flow, which consists of the sum of the delays at the individual nodes, improves by granting a larger share of the medium capacity to the bottleneck node. Such alternative resource sharing strategies can be enforced in real systems by deploying the recently standardized ieee 802.11emac-protocol. We propose a mapping between the parameter settings of ieee 802.11e and the fluid-flow model, and validate the fluid-flow model and the parameter mapping with detailed system simulations. [ABSTRACT FROM AUTHOR]

As the use of WLANs based on IEEE 802.11 increases, the need for QoS becomes more obvious. The new IEEE 802.11e standard aims at providing QoS, but its contention-based medium access mechanism, EDCA, provides only service differentiation, i.e. soft QoS. In order to provide hard QoS, earlier we have proposed an extension called EDCA with resource reservation (EDCA/RR), which enhances EDCA by offering also hard QoS through resource reservation. In this paper, we extend EDCA/RR to cope with the hidden terminal problem, outline a solution for multi-hop scenarios, and compare the proposed scheme with EDCA. [ABSTRACT FROM AUTHOR]

In the Internet, a variety of entities competes with each other. For example, coexisting overlay networks compete for physical network resources and they often disrupt each other. Service providers offer different services and compete for network resources and customers. If competitors could establish cooperative relationships, the collective performance can be improved and they can coexist peacefully and comfortably in a shared environment. In this paper, to understand the way that symbiosis emerges from direct and/or indirect interactions among coexisting entities in a shared environment, we adopt a mathematical model of symbiotic strains. Through thorough evaluations, we show that networks of different service rate and resource consumption can coexist by mutual interactions. [ABSTRACT FROM AUTHOR]

In todays Internet, a trend towards distributed content delivery systems can be observed. These systems still have to offer the same functionality as centralized architectures, e.g. content localization. While several advantages like load distribution and cost reduction could be gained by using a decentralized distribution platform, they come with a tradeoff in resource consumption. In this paper, we analyze and evaluate a decentralized Content Distribution Application (CDA) with respect to the time needed to locate specific content. We introduce a node model based on queueing theory and provide methods to compute important characteristics like the mean search time. In this model, we do not only consider the external offered load, but also the internal traffic created as a consequence of decentralization. [ABSTRACT FROM AUTHOR]

Broadband satellite-based IP networks have been considered as the technology to enable a strong and promising next-generation market. In satellite communication systems, the channel performance might be severely degraded due to the dynamic weather conditions such as the precipitation, and thereby lead to network congestion. Therefore, congestion control is critical in such networks to satisfy QoS based Service Level Agreement (SLA). Moreover, the inherent large bandwidth-delay product of satellite channels impedes the deployment of existing numerous congestion control schemes. In this paper, we propose a modified Random Early Detection (RED) based congestion avoidance/control mechanism that incorporates a fuzzy logical controller to tune the queue thresholds of RED according to the dynamic weather conditions. We will show using analysis and simulations that the newly developed congestion control method is effective and efficient for broadband satellite-based IP networks. [ABSTRACT FROM AUTHOR]

Semi-Markov processes (SMPs) are widely used to model various types of data traffic in communication networks. Also, efficient and reliable analysis techniques are available. In this paper, we consider several present methods of deriving the parameters of a discrete-time semi-Markov process from given H.264 video traces in order to model the original traffic adequately. We take the distribution of frame sizes and the autocorrelation of both the original trace and the resulting SMP model into account as key quality indicators. We propose a new evolutionary optimization approach using genetic programming, which is able to significantly improve the accuracy of semi-Markov models of video traces and, at the same time, requires a smaller number of states. [ABSTRACT FROM AUTHOR]

IPTV over DSL access networks is becoming a reality. This paper studies the impact of the presence of a video-aware traffic management module in the access network on the performance of the video dejittering mechanism at the receiver. The presented numerical results illustrate that with the traffic management module, the packet loss probability at the dejittering buffer decreases. Since the traffic management module will only drop the least important enhancement layer packets of the video in case of congestion, especially the important base layer packets of the video gain from the use of the traffic management module. All results in this paper are obtained using a mathematical model. [ABSTRACT FROM AUTHOR]

The paper considers a problem of routing, protection and load balancing in the IP/MPLS network. A network design problem combining all these aspects is presented. Proportionally fair distribution of residual bandwidths on links is used for load balancing, and protection is achieved with failure-dependent backup paths. The efficiency of the proposed approach is tested by combining optimization and simulation tools. Numerical experiments show that using the proposed load balancing and protection mechanisms decreases the number of disrupted LSPs in case of failures, as compared to other recovery options considered. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the performance of multicast protocols for wireless mobile ad hoc networks (MANETs). Recently, there have been several proposals to reduce overhead and enable scalability in respect to the number of multicast members. Explicit multicast protocols, which differ from common approaches proposed for MANET multicast routing, are based on the Xcast scheme and intends to reduce energy consumption. These protocols are best suited for use with Small Multicast Groups operating in dynamic networks of any size. Classical multicast protocols which are tree based or mesh based are more appropriate for large scale multicast group. We evaluate the performance of EM2NET, an Explicit Multicast Protocol for MANET, with other multicast protocols proposed for ad hoc networks via extensive and detailed simulation. The performance differentials are analyzed using varying network load, mobility and multicast group size in order to provide a qualitative assessment of the applicability of the protocols in different scenarios. Results indicate that EM2NET offers better energy conservation and also supports mobility better than existing explicit protocols. [ABSTRACT FROM AUTHOR]

The multiple expected sources of traffic skewness in Next- Generation SensorNets (NGSN) will trigger the need for load-balanced point-to-point routing protocols. Driven by this fact, we present in this paper a load-balancing primitive, namely Traffic-Oblivious Load-Balancing (TOLB), to be used on top of any point-to-point routing protocol. TOLB obliviously load balances traffic by pushing the decision-making responsibility to the source of any packet without depending on the energy status of the network sensors or on previously taken decisions for similar packets. We present theoretical bounds on TOLB's performance for special network types such as mesh networks. Additionally, we ran simulations to evaluate TOLB's performance on general networks. Our experimental results show the high benefit (in terms of network lifetime and throughput) of applying TOLB on top of routing schemes to deal with various traffic skewness levels in different sensor deployment scenarios. [ABSTRACT FROM AUTHOR]

The increased use of ubiquitous computing devices is resulting in networks that are highly mobile, well connected and growing in processing and storage capabilities. The nature of these ubiquitous systems, however, also increases the risk of building systems that are undependable and potentially insecure. This paper investigates the use of autonomous agents combined with an intrusion tolerance technique for providing secure and dependable storage for ad hoc networks. The proposed approach is based on the fragmentation-redundancy-scattering (FRS) technique that is able to tolerate both accidental and intentional faults by fragmenting confidential information into insignificant fragments, and by scattering these fragments in a redundant fashion across a network. Two algorithms that are able to maintain a constant number of fragments replicas were developed for this study: one based on the game of life, and the other based on roaming ants. Both algorithms were simulated in NetLogo, and simulated further in a cluster of computers for evaluation of their scalability. [ABSTRACT FROM AUTHOR]

In this paper, we propose an efficient and practical routing scheme for MANETs based on a new routing metric called the free-degree of nodes. In the proposed routing scheme named FDAR (Free-Degree Adaptive Routing), it is intended to deliver data packets circumventing congested routes, so as to realize a short end-to-end delay and a moderate load balancing of the overall network. In addition, it tries to avoid frequent and unnecessary invocation of route discovery process which would significantly degrade the routing performance of the MANET. The effectiveness of the proposed scheme is evaluated by simulation. The result of simulations indicates that it certainly outperforms previous load-balanced routing schemes including DLAR and LBAR, in terms of the packet loss rate and the average end-to-end delay. [ABSTRACT FROM AUTHOR]

The success of authentication mechanisms, intrusion detection and response systems, and other security measures to protect MANET from attack are very much dependant on nodes' cooperation. Ensuring a node's cooperation is very challenging in a MANET environment because of the nature of such a network; consisting of a set of anonymous nodes that operate independently, without the existence of a central authority to enforce them to cooperate. One of the solutions for this problem is by creating a trust chain between nodes to create a trusted community. This paper discusses some of the existing studies that have been proposed to overcome this issue and proposes a novel trust framework based upon a friendship concept. Results from simulation experiments proved that the proposed trust framework is capable of creating a trusted community in MANET, whilst at the same time addressing limitations of existing trust frameworks. [ABSTRACT FROM AUTHOR]

The in-network aggregation and processing of information is what sets a sensor network apart from a pure data acquisition device. One way to model the exchange of information between the network nodes is to distinguish between nodes that are producers of information, i.e., those that have collected data, detected events, etc., and nodes that are consumers of information, i.e., nodes that seek data or events of certain types. In this paper we aim to support that exchange of information via a so-called information brokerage scheme. Main features of our proposed scheme are that 1) it works in a location-free setting where nodes are unaware of their geographic locations 2) it is robust to non-regular network topologies and 3) it does not require the information producers and consumers to know of each other. Our proposed scheme employs boundary detection algorithms which only quite recently have been developed to extract geometry and topology information even in location-free network deployments. [ABSTRACT FROM AUTHOR]

Sensor networks are wireless adhoc networks where all the nodes cooperate for routing messages in the absence of a fixed infrastructure. Non-flooding, guaranteed delivery routing protocols are preferred because sensor networks have limited battery life. Location aware routing protocols are good candidates for sensor network applications, nevertheless they need either an external location service like GPS or Galileo (which are bulky, energy consuming devices) or internal location services providing non-unique virtual coordinates leading to low delivery rates. In this paper we introduce Position Trees a collision free, distributed labeling algorithm based on hop counting, which embed a spanning tree of the underlying network . The Routing with Position Trees (RTP) is a guaranteed delivery, non-flooding, efficient implicit routing protocol based on Position Trees. We study experimentally the statistical properties of memory requirements and the routing efficiency of the RPT. [ABSTRACT FROM AUTHOR]

Nowadays WSNs support applications such as target tracking, environmental control or vehicles traffic monitoring. Generally, these applications have strong and strict requirements for end-to-end delaying and loosing during data transmissions. In this paper, we propose a practical scenario for application of the WSN field in order to illustrate selection of an appropriate approach for guaranteeing performance in a WSN-deployed application. The methodology we have used includes four major phases: 1) Requirements analysis of the application scenario; 2) QoS modelling in different layers of the communications protocol stack and selection of more suitable QoS protocols and mechanisms; 3) Definition of a simulation model based on an application scenario, to which we applied the protocols and mechanisms selected in phase 2; 4) Validation of decisions by means of simulation; and 5) analysis of results. This work has being partially developed in the framework of the CRISAL - M0700204174 project (partially funded by "Universidad Politécnica de Madrid" and "Comunidad de Madrid", Spain). [ABSTRACT FROM AUTHOR]

Self-organizing systems are present in many areas of nature and science, and have more recently been increasingly applied to telecommunications. These systems often exhibit common structural properties, such as the small-world property, and can react to changes in their environment with no centralized control. With ever-increasing capacity requirements, Transparent Optical Networks (TONs) have been established as the enabling technology for future long-haul high-speed backbone networks. Designing fast security mechanisms is critical, particularly due to the high speeds and transparency inherent in TONs. In this paper, we propose a self-organizing small-world control plane for failure management in TONs, which can improve scalability and adapt to changes in the network. [ABSTRACT FROM AUTHOR]

In this paper, we investigate how to incorporate an application metric into the construction of a multicast tree so as to facilitate the use of range constrained multicast. We first describe the construction and delivery protocols, show through an analysis drawing on stochastic geometry that the protocol is scalable, and provide simulations showing the performance of the protocol against trees derived from reverse path forwarding construction. [ABSTRACT FROM AUTHOR]

A knowledge network is a generic structure that organises distributed knowledge into a system that will allow it to be efficiently retrieved. The primary features of this network are its lightweight autonomous framework. The framework allows for smaller components such as pervasive sensors to operate. Stigmergy is thus the preferred method to allow the network to self-organise and maintain itself. To be able to return knowledge, the network must be able to reason over its stored information. As part of the query process, links can be stigmergically created between related sources to allow for query optimisation. This has been proven to be an effective and lightweight way to optimise. These links may also contain useful information for providing knowledge. This paper considers a number of possibilities for using these links to return knowledge through a distributed lightweight reasoning engine, thus upholding the main features of the network. [ABSTRACT FROM AUTHOR]

We consider load sharing in distributed systems where a stream of service requests arrives at a collection of n identical servers. The goal is to provide the service with the lowest possible average waiting time. This problem has been extensively studied before, but most previous models have not incorporated the monitoring costs explicitly. This paper focuses on a rigorous study of maximizing the utility of monitoring. We extend the Supermarket Model for dynamic load sharing by explicitly incorporating monitoring costs. These costs stem from the fact that the servers have to answer load queries, a task which consumes both CPU and communication resources. This Extended Supermarket Model (ESM) allows us to formally study the tradeoff between the usefulness of monitoring information and the cost of obtaining it. In particular, we prove that for each service request rate, there exists an optimal number of servers that should be monitored to obtain minimal average waiting time. Based on this theoretical analysis, we develop an autonomous load sharing scheme that adapts the number of monitored servers to the current load. We evaluate the performance of this scheme using extensive simulations. It turns out that in realistic scenarios, where monitoring costs are not negligible, the self-adaptive load balancing scheme is clearly superior to any load-oblivious load sharing mechanisms. [ABSTRACT FROM AUTHOR]

A system is said to be self-organizing if its execution yields temporal global structures out of simple and local interactions amongst its constituents (e.g agents, processes). In nature, one can find many natural systems that achieve organization at the global level without a reference to the status of the global organization; real examples include ants, bees, and bacteria. The future of tuple-space systems such as Linda lies on (i) their ability to handle non-trivial coordination constructs common in complex applications, and (ii) their scalability to environments where hundreds and maybe thousands of nodes exist. The Achilles heel of scalability in current tuple-space systems is tuple organization. Legacy solutions based on antiquated approaches such as hashing are (unfortunately) commonplace. This paper gets inspiration from self-organization to improve the status quo of tuple organization in tuple-space systems. We present a solution that organizes tuples in large networks while requiring virtually no global knowledge about the system. [ABSTRACT FROM AUTHOR]

In many scenarios, self-organization is the driving force for the use of a peer-to-peer (p2p) network. However, most current p2p networks are not truly self-organizing, as little attention has been paid on how new nodes join a p2p network, the so-called bootstrapping. Current p2p network protocols rely on prior-knowledge of nodes like a list of IP addresses of bootstrap servers or like a list of known peers of a p2p network. However, this kind of prior knowledge conflicts with the self-organization principle and the distributed character of p2p networks. In this paper, we present the design of a generic, self-organizing, and distributed bootstrap service which can be used to bootstrap p2p networks of arbitrary size, even very small, private p2p networks. This bootstrap service works in today's Internet and it can be easily integrated into existing p2p applications. We present an evaluation of the proposed bootstrapping service showing the efficiency of our approach. [ABSTRACT FROM AUTHOR]

A routing protocol is designed considering a particular environment all the time which is not possible in the case of practical ad hoc networks. Because of the uncertainty in topological rate of change, mobility model, and terrain condition, the performance is severely degraded. So the concept of assigning single routing protocol does not address the problem of most modern day mobile networks. Instead, the feedback-based routing protocol which is highly adaptable in changing environment is more suitable and this concept has been proposed in this paper. The mathematical modeling of feedback parameters have been designed and analyzed for the highly unstable networks. Some of the parameters we measure here are network connection ratio, end-to-end connectivity, packet delivery ratio, and number of nodes. Those are functionally related with the routing parameter. [ABSTRACT FROM AUTHOR]

In this paper, we first analyze the medium access delay of a packet in a terminal in the saturated IEEE 802.11 network. In our analysis, we use the renewal theory to analyze the detailed packet transmission processes of terminals in the network such as the backoff counter freezing. Using our detailed analysis of the packet transmission processes of terminals, we analyze the packet transmission process of a tagged terminal and the background traffic for the tagged terminal which is generated by non-tagged terminals, and derive the Laplace transform of the medium access delay of a packet under the saturated condition. Next, based on the analysis of the medium access delay under the saturated condition, we propose a mathematical model to analyze the packet overflow probability of an unsaturated terminal. We also provide numerical and simulation results to validate our analysis and investigate the characteristics of the system performance. IEEE 802.11 WLAN, Distributed Coordination Function, Medium Access Delay, Performance Evaluation, Packet Overflow Probability [ABSTRACT FROM AUTHOR]

In this paper we consider a problem of implementing a hybrid routing protocol for wireless sensor networks, which natively supports data-centric, geographic-based and address-centric communication paradigms. We demonstrate the feasibility of such protocol by presenting tinyLUNAR, an adapted to the specifics of sensor networks reactive routing scheme originally developed for mobile wireless ad hoc networks. In addition to the support for several communications paradigms tinyLUNAR implements highly efficient multihop forwarding using only 1 B field that can be directly encoded in the standard IEEE 802.15.4 MAC header. [ABSTRACT FROM AUTHOR]

Network-based Localized Mobility Management (NetLMM) is an outstanding candidate solution for the mobility management controlled by the network. In NetLMM, mobile nodes (MNs) can be provided mobility services without any installation of mobility-support stack. However, there is a restriction that the MN is able to have the mobility only within a single localized mobility domain (LMD). In this paper, we propose a novel Inter-LMD handoff mechanism in order to eliminate the shortcoming of the current NetLMM protocol. The proposed Inter-LMD handoff mechanism enables that the MN hands off across LMDs, even if the MN does not have a functionality of Mobile IPv6 (MIPv6). According to the performance evaluation, the proposed Inter-LMD handoff mechanism has approximately 5.8% more overhead than the current Inter-LMD handoff of MIPv6-capable devices, while the current NetLMM protocol does not support the handoff of MIPv6-incapable devices. [ABSTRACT FROM AUTHOR]

Existing wireless networks have little in common, as they are designed around vendor-specific devices that use specific radio access technologies to provide particular functionality. Next generation networks seek to integrate wired and wireless networks in order to provide seamless services to the end user. Seamless Mobility is an experiential architecture, predicated on providing mechanisms that enable a user to accomplish his or her tasks without regard to technology, type of media, or device. This paper examines how autonomic mechanisms can satisfy some of the challenges in realizing seamless mobility solutions. [ABSTRACT FROM AUTHOR]

In location tracking, there is a trade-off between data accuracy of mobile targets and energy efficiency of sensor nodes. If the number of nodes is increased to track a mobile target, the level of data accuracy increases, but the energy consumption of nodes increases. In this paper, we propose a new location tracking scheme that considers these two factors. The proposed scheme is designed to track mobile targets in a cluster-based sensor network. In order to increase the energy efficiency of sensor nodes, a portion of nodes that detect the mobile target is selected to track the target using the backoff procedure. In addition, we consider data accuracy as controlling the number of nodes by varying the transmission range of the nodes. We perform a simulation to evaluate the performance of the proposed scheme over sensor networks. We provide simulation results comparing the proposed scheme with the general approach. The simulation results show that the proposed scheme has the excellent performance over a broad range of parameters. [ABSTRACT FROM AUTHOR]

A potential solution for building ad-hoc networks is described. It is based on the Technoconcepts' TSR chipset. This chipset provides direct conversion of RF signals to baseband. Such RF/DTM chips convert the received signals into digital form immediately after the antenna, making it possible to provide all required signal processing in digital form, thus allowing adaptive frequency bands free of interference. This flexibility provides the most favorable conditions for quality communications. The offered solution has its own set of challenges. The paper describes the major challenges, and the potential ways of addressing them. An example of possible ad-hoc network architectures is presented that is based on the RF/DTM chips. [ABSTRACT FROM AUTHOR]

The functioning of an ad hoc network is based on the supportive contributions of all of its members. Nodes behave as routers and take part in route discovery and maintenance. In this paper, a forwarding protocol is presented that stimulates node cooperation to improve the throughput of the network. The incentive mechanism is provided through a micropayment protocol that deals with the cooperation range of the users. Most cooperative nodes intrinsically benefit of the best routes and availability and they take preference in front of selfish ones. [ABSTRACT FROM AUTHOR]

In telecommunications networks, usually an aggregation of information units (a batch) is transmitted instead of individual information units. In order to obtain performance measures for such networks, we analyze a discrete-time queueing model with a batch server operating under the minimum batch size (MBS) service policy. Specifically, we calculate the steady-state probability generating function (PGF) of the system contents at the beginning of an arbitrary slot. This PGF enables us to derive some important performance measures. Furthermore, we investigate, through some numerical examples, the influence of some parameters on the optimal choice of the MBS. In this paper, we focus on the influence of the load and the distribution of the service times. [ABSTRACT FROM AUTHOR]

Mobile WiMAX is a promising wireless technology approaching market deployment. Much discussion concentrate on whether mobile WiMAX will reach a tipping point and become 4G or not. As a pre-mobile WiMAX system is being delivered, we decided to set up a real life field trial and perform the most important measurements over the system setup. The system was delivered with 4th order diversity. In this paper we analyze physical system performance based on field trial measurements, especially at locations with non line of sight conditions in urban areas. We investigate the gain with 2nd and 4th order base station diversity and derive analytical expressions. The system path loss is plotted and found to approach the Cost-231 Hata model for urban areas. Throughput is also measured and analyzed. Sub-channelization in the uplink points out to be an important feature for enhanced coverage. [ABSTRACT FROM AUTHOR]

The performance of a TCP protocol on MANETs has been studied in a numerous researches. It has been shown that performance of TCP on MANET is poor and that it is caused by two groups of reasons: one inherited from wireless networks and one caused by nodes mobility. One reason of TCP degradation is inability to distinguish between packet losses due to congestion from those caused by nodes mobility and as consequence broken routes. This paper presents the Cluster-Label-based Routing protocol that is an attempt to compensate source of TCP problems on MANETs - multi-hop mobile environment. By utilizing Cluster-Label-based mechanism for Backbone the CLR is able to concentrate on detection and compensation of movement of a destination node. The proposed protocol provides better goodput and delay performance than standardized protocols especially in cases of large network size and/or high mobility rate. [ABSTRACT FROM AUTHOR]

Real-time traffic aggregates are often characterized by time-varying nature. However, resources for this kind of traffic are usually allocated assuming busy hour stationary traffic characteristics. This assumption may lead to inefficient use of network resources when static resource reservation is used. In this paper we propose the algorithm for on-line estimation of the traffic state in terms of piecewise weakly stationary stochastic process. As a basic tool of the algorithm we use change-point statistical test allowing us to dynamically and automatically determine whether the traffic pattern changes and, if so, estimate new parameters of the traffic pattern. Assuming that a network may assign the required resources on-demand on a per-node basis, the proposed procedure helps to decide which amount of resources should be assigned to handle the traffic with given performance metrics. The proposed algorithm is well-suited for non-stationary behavior of the aggregated traffic where statistical parameters change in time. The computational complexity of the algorithm is low and it can be implemented on a traffic class basis making the proposal suitable for backbone routers. [ABSTRACT FROM AUTHOR]