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Estudio y análisis del comportamiento de redes ad hoc móviles para supervisión de procesos en entornos industriales
Abstract
El uso de las redes inalámbricas tiene un impacto creciente en la industria moderna (sistemas de automoción y fabricación industrial, sistemas distribuidos de supervisión y control...). Especialmente las redes inalámbricas han penetrado de forma rápida en las redes de control que dan soporte a servicios públicos estratégicos (suministro de gas y electricidad, suministro y saneamiento de aguas). Estas redes están formadas por distintas estaciones remotas, una estación central donde se procesa, almacena y controla la información de la instalación y varios clientes remotos que también supervisan y controlan la instalación remotamente. Para comunicar las estaciones remotas con la estación central se utilizan infraestructuras de comunicaciones heterogéneas según las posibilidades y ubicación: xDSL, HFC, WiMAX, GPRS, UMTS, HSDP. Para que el sistema sea eficiente y útil, especialmente en momentos de emergencia, los usuarios ubicados en las estaciones remotas necesitan intercambiar información entre sí o con la estación central. En estos casos, en las estaciones remotas, los propios usuarios que están supervisando el funcionamiento de la instalación haciendo uso de sus dispositivos inalámbricos pueden crear de forma espontánea una red ad hoc móvil útil para el intercambio de información en el caso de que origen y destino no se alcancen directamente. El objetivo global de la tesis es analizar el comportamiento de las MANET en entornos de tipo industrial, tomando como ejemplo una red para el control y supervisión de la red de saneamiento de una gran ciudad, y estudiar cómo afecta a su funcionamiento y a los servicios ofrecidos el movimiento de los nodos. Aunque son muchos los avances realizados en el estudio de las redes ad hoc en los últimos años, aún quedan muchos aspectos que necesitan ser estudiados y mejorados. Pocos han sido los trabajos que evalúen las redes ad hoc con modelos formales.
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This document describes the Optimized Link State Routing (OLSR)
protocol for mobile ad hoc networks. The protocol is an optimization
of the classical link state algorithm tailored to the requirements of
a mobile wireless LAN. The key concept used in the protocol is that
of multipoint relays (MPRs). MPRs are selected nodes which forward
broadcast messages during the flooding process. This technique
substantially reduces the message overhead as compared to a classical
flooding mechanism, where every node retransmits each message when it
receives the first copy of the message. In OLSR, link state
information is generated only by nodes elected as MPRs. Thus, a
second optimization is achieved by minimizing the number of control
messages flooded in the network. As a third optimization, an MPR
node may chose to report only links between itself and its MPR
selectors. Hence, as contrary to the classic link state algorithm,
partial link state information is distributed in the network. This
information is then used for route calculation. OLSR provides
optimal routes (in terms of number of hops). The protocol is
particularly suitable for large and dense networks as the technique
of MPRs works well in this context.
This document describes the Optimized Link State Routing (OLSR)
protocol for mobile ad hoc networks. The protocol is an optimization
of the classical link state algorithm tailored to the requirements of
a mobile wireless LAN. The key concept used in the protocol is that
of multipoint relays (MPRs). MPRs are selected nodes which forward
broadcast messages during the flooding process. This technique
substantially reduces the message overhead as compared to a classical
flooding mechanism, where every node retransmits each message when it
receives the first copy of the message. In OLSR, link state
information is generated only by nodes elected as MPRs. Thus, a
second optimization is achieved by minimizing the number of control
messages flooded in the network. As a third optimization, an MPR
node may chose to report only links between itself and its MPR
selectors. Hence, as contrary to the classic link state algorithm,
partial link state information is distributed in the network. This
information is then used for route calculation. OLSR provides
optimal routes (in terms of number of hops). The protocol is
particularly suitable for large and dense networks as the technique
of MPRs works well in this context.
The random waypoint model is a commonly used mobility model for simulations of wireless communication networks. By giving a formal description of this model in terms of a discrete-time stochastic process, we investigate some of its fundamental stochastic properties with respect to: (a) the transition length and time of a mobile node between two waypoints, (b) the spatial distribution of nodes, (c) the direction angle at the beginning of a movement transition, and (d) the cell change rate if the model is used in a cellular-structured system area.The results of this paper are of practical value for performance analysis of mobile networks and give a deeper understanding of the behavior of this mobility model. Such understanding is necessary to avoid misinterpretation of simulation results. The movement duration and the cell change rate enable us to make a statement about the “degree of mobility” of a certain simulation scenario. Knowledge of the spatial node distribution is essential for all investigations in which the relative location of the mobile nodes is important. Finally, the direction distribution explains in an analytical manner the effect that nodes tend to move back to the middle of the system area.
Distance-based and movement-based location update (LU) strategies are usually selected when dynamic location management schemes are employed. The distance-based outperforms the movement-based mech- anism, even though the former requires that each mobile terminal stores all identifiers of those cells within its registration area. These strategies are often studied using the random walk mobility model, that yields a lower cost for the distance-based scheme. However, if a directional mobility pattern is considered the distance-based LU cost increases and it approaches the movement-based LU cost. In such cases, movement- based policies may be more suitable for its simplicity rather than distance-based schemes. In this paper, we propose a random-directional model which generalizes the random walk model. Our proposal gathers mobility patterns with several degrees of randomness, so that both random walk and totally directional mobility patterns are modeled. This model is applied to study and compare the costs of the distance-based and the movement-based policies as a function of the directional movement. Both one-step paging and selective paging strategies are considered to compute these costs.
In this paper we present an experimental evaluation of a full ad hoc network architecture with particular attention to routing and middleware layers. In particular we set up a MANET prototype on which we performed a large set of experiments: in a first phase, we analyzed performances of a proactive and a reactive routing protocols in case of low mobility scenarios in small-medium scale ad hoc networks; then we studied the performances of a first prototype of an optimized p2p system for ad hoc networks (CrossROAD), based on a cross-layer interaction with a proactive routing protocol. Our analysis shows that the use of a proactive routing protocol does not negatively influence system performances, furthermore it allows the optimization of a structured p2p system on ad hoc networks, providing a complete and timely updated knowledge of the network topology. In this way, the overlay network is completely self-organizing and correctly manages network partitioning and topology changes.
The Efficient routing protocols can provide significant benefits to mobile ad hoc networks, in terms of both performance and reliability. Many routing protocols for such networks have been proposed so far. Amongst the most popular ones are Ad hoc On-demand Distance Vector (AODV), Destination-Sequenced Distance-Vector Routing protocol (DSDV), Dynamic Source Routing Protocol (DSR), and Optimum Link State Routing (OLSR). Despite the popularity of those protocols, research efforts have not focused much in evaluating their performance when applied to variable bit rate (VBR). In this paper we present our observations regarding the performance comparison of the above protocols for VBR in mobile ad hoc networks (MANETs). We perform extensive simulations, using NS-2 simulator. Our studies have shown that reactive protocols perform better than proactive protocols. Further DSR has performed well for the performance parameters namely delivery ratio and routing overload while AODV performed better in terms of average delay.
Stochastic extensions to Petri nets have gained widespread acceptance as a method for describing the dynamic behavior of discrete-event
systems. Both simulation and analytic methods have been proposed to solve such models. This paper describes a set of efficient
procedures for simulating models that are represented as stochastic activity networks (SANs, a variant of stochastic Petri
nets) and composed SAN-based reward models (SBRMs). Composed SBRMs are a hierarchical representation for SANs, in which individual
SAN models can be replicated and joined together with other models, in an iterative fashion. The procedures exploit the hierarchical
structure and symmetries introduced by the replicate operation in a composed SBRM to reduce the cost of future event list
management. The procedures have been implemented as part of a larger performance-dependability modeling package known asUltraSAN, and have been applied to real, large-scale applications.
The industrial world has been thinking since a couple a years of the use of wireless technologies in its environment despite the implementation of an ideal industrial wireless standard. However, the industrial environments are not taken into consideration in the design of those standards, because its harsh constraints has specific characteristics (reliability, interferences with existing equipments, multi-path propagation, low-power consumption, real-time reconfiguration, security...) that need specific requirements and eventually standards. This paper will present the scope of the wireless technologies from a technical perspective, the constraints that the industrial environment imply on wireless networks and namely on the radio transmission, finally giving axes of solutions and elements of the current deployments if wireless technologies in EDF (Electricite de France). Our current works showed us that there is no perfect technology by it-self but the best trade-off solution is a hybrid architecture combining the right wired and wireless technologies.
With the increased focus on the availability of complex, multifunction systems, modeling processes and analysis tools are needed that help the availability systems engineer understand the impact of architectural and logistics design choices concerning system availability. Because many fielded systems are required to achieve a specified minimal availability over a short measurement period, a modeling methodology must also support computation of the distribution of operational availability for the specified measurement period. This paper describes a two-part behavior-based availability achievement risk methodology that starts with a description of the system's availability related behavior followed by a stochastic activity network-based simulation to obtain numeric estimate of expected availability and the distribution of availability over a selected time frame. The process shows how the system engineer freed to explore complex behavior not possible with combinatorial estimation methods in wide use today
This paper presents experiments on the performance and the viability of the AODV protocol (Ad hoc On-demand Distance Vector protocol) in multi-hop ad hoc networks, for use with multimedia traffic. This type of traffic presents some particular characteristics which make it difficult for AODV to serve fluently and reliably. After this experimental study of the problems that may arise in this type of communication and its origins, we conclude that better performance is possible with the modification of some of the protocol's parameters, without modifying the protocol algorithm. Applying these changes, experimental tests show an improvement in the performance of the protocol with video streaming.
This paper presents an alternative simple loop-free bandwidth-efficient distributed routing algorithm for mobile ad hoc networks, denoted as distributed dynamic, routing (DDR). Although DDR benefits from classical concepts like zone and forest, unlike previous solutions it achieves several goals at the same time. Firstly, it provides different mechanisms to drastically reduce routing complexity and improve delay performance. Secondly, it is an infrastructureless in a strong sense: it does not even require a physical location information. Finally, zone naming is performed dynamically and broadcasting is reduced noticeably.
An ad-hoc network is the cooperative engagement of a collection of
mobile nodes without the required intervention of any centralized access
point or existing infrastructure. We present Ad-hoc On Demand Distance
Vector Routing (AODV), a novel algorithm for the operation of such
ad-hoc networks. Each mobile host operates as a specialized router, and
routes are obtained as needed (i.e., on-demand) with little or no
reliance on periodic advertisements. Our new routing algorithm is quite
suitable for a dynamic self starting network, as required by users
wishing to utilize ad-hoc networks. AODV provides loop-free routes even
while repairing broken links. Because the protocol does not require
global periodic routing advertisements, the demand on the overall
bandwidth available to the mobile nodes is substantially less than in
those protocols that do necessitate such advertisements. Nevertheless we
can still maintain most of the advantages of basic distance vector
routing mechanisms. We show that our algorithm scales to large
populations of mobile nodes wishing to form ad-hoc networks. We also
include an evaluation methodology and simulation results to verify the
operation of our algorithm
Our experiments with IEEE 802.11b based wireless ad hoc networks show that neighbor sensing with broadcast messages introduces "communication gray zones": in such zones data messages cannot be exchanged although the HELLO messages indicate neighbor reachability. This leads to a systematic mismatch between the route state and the real world connectivity, resulting in disruptive behavior for multi-media data transfer over ad hoc routing protocols. Concentrating on AODV we explore this issue and evaluate three different techniques to overcome the gray zone problem. We present quantitative measurements of these improvements and discuss the consequences for ad hoc routing protocols and their implementations.
Urban facility interconnection networks require a robustness and reliability usually found in public networks or private cable and radio networks in licensed bands. Both factors mean an increase in costs, which also increase as the size of the network increases. The recent rise in use of wireless technologies in open wavebands has attracted the interest of the industry in the spread of these types of links, even though they have a lower level of robustness and reliability, which must be improved using communication mechanisms and protocols. This aspect directly affects real time applications, such as VoIP and video-streaming, and determines the viability of these systems in real installations. This paper evaluates the performance of control and real time multimedia traffic in the 5 GHz band through the use of the SIP (Session Initiation Protocol) and RTP (Real-Time Transport Protocol) protocols, in a laboratory testbed.
The random waypoint model is a commonly used mobility model for simulations of wireless communication networks. In this paper, we present analytical derivations of some fundamental stochastic properties of this model with respect to: (a) the length and duration of a movement epoch, (b) the chosen direction angle at the beginning of a movement epoch, and (c) the cell change rate of the random waypoint mobility model when used within the context of cellular networks. Our results and methods can be used to compare the random waypoint model with other mobility models. The results on the movement epoch duration as well as on the cell change rate enable us to make a statement about the 'degree of mobility' of a certain simulation scenario. The direction distribution explains in an analytical manner the effect that nodes tend to move back to the middle of the system area.
A mobile ad hoc network consists of wireless hosts that may move often. Movement of hosts results in a change in routes, requiring some mechanism for determining new routes. Several routing protocols have already been proposed for ad hoc networks. This paper suggests an approach to utilize location information (for instance, obtained using the global positioning system) to improve performance of routing protocols for ad hoc networks. By using location information, the proposed Location-Aided Routing (LAR) protocols limit the search for a new route to a smaller "request zone" of the ad hoc network. This results in a significant reduction in the number of routing messages. We present two algorithms to determine the request zone, and also suggest potential optimizations to our algorithms.
Wireless Local area networks (wLANs), particularly from standards 802.1b/g, have become extremely widespread in a very short time, in society in general as well as at an industrial level. One of the limitations of this technology is its coverage. The family of new standards, such as 802.16, allows us to overcome these limitations, enabling then their use as Metropolitan Area Networks (MAN), as required by some application domains of industrial networks. In the present work we present an application of this technology in telemonitoring systems on metropolitan areas which shows their potential, but also the complexity of predicting their behaviour in a dynamic scenario such as a large city.
In this paper we describe a real-time industrial communication network able to support both control-related and multimedia traffic. The industrial communication network is based on the PROFIBUS standard, with multimedia capabilities. The TCP/IP suite of protocols, properly integrated within the PROFIBUS communication stack, supports these capabilities. From the timeliness point of view the challenge is two folded. On one hand the multimedia traffic should not interfere with the timing requirements of the ‘‘native‘’ control-related PROFIBUS traffic (typically hard real-time). On the other hand multimedia traffic requires certain levels of quality-of-service to be attained. Copyright © 2001 IFAC
Topology Dissemination Based on Reverse-Path Forwarding (TBRPF) is a proactive, link-state routing protocol designed for mobile ad-hoc networks, which provides hop-by-hop routing along shortest paths to each destination. Each node running TBRPF computes a source tree (providing paths to all reachable nodes) based on partial topology information stored in its topology table, using a modification of Dijkstra's algorithm. To minimize overhead, each node reports only *part* of its source tree to neighbors. TBRPF uses a combination of periodic and differential updates to keep all neighbors informed of the reported part of its source tree. Each node also has the option to report additional topology information (up to the full topology), to provide improved robustness in highly mobile networks. TBRPF performs neighbor discovery using "differential" HELLO messages which report only *changes* in the status of neighbors. This results in HELLO messages that are much smaller than those of other link-state routing protocols such as OSPF.
Recently, much attention has been given to the need to endow industrial communication networks used in real-time systems with flexible scheduling. This allows control systems to adapt to the variations in the requirements of traffic generated by modifications in the environment of the system, or changes in its structure. Another active area is multimedia transmission in industrial environments. In this paper, a flexible
scheduling system for Profibus networks is presented. There are two objectives. Firstly to allow the characteristics of real-time traffic to deal in run time in a fieldbus and secondly to enable the scheduling of video traffic for industrial monitoring purposes. The system proposed allows, with regard to traditional Profibus MAC/scheduling, rapid dynamic adaptation to the new requirements, minimizing the bandwidth necessary for its management and maximizing the use of the available bandwidth. As a result there is an improvement in quality of video sources as well as the number of video sources, which can co-exist with the control traffic, without affecting its QoS.
Automation based on distributed control systems (DCS) technology enormously increases the plant supervision capability of a single human. For example, DCSs over broadband networking makes possible the integration and operation of a country-wide electricity generation and distribution system. Out-of-plant supervision is, however, more risky due to the impossibility of direct plant observation and exclusive reliance on digital data systems for decision making. This paper describes a distributed system based on CORBA technology to provide real-time visual feedback to operators of such a large supervision system. 2001 Elsevier Science Ltd. All rights reserved.
Les réseaux locaux industriels diffèrent des autres types de reseaux car leurs applications sont responsables de la commande
et de la surveillance ďun processus physique. Dans cet article, les auteurs résument les spécifications des utilisateurs de
ces réseaux, présentent ľétat de ľart dans le domaine des réseaux de terrain, de cellule et ľusine et donnent les directions
de recherches actuelles.
Industrial communication networks differ from other types of networks because these applications are responsible for the control
and monitoring of a physical process. In this paper, we will summarise the requirements that users specify for these networks,
present the state of art on field buses, factory and cell communication networks and indicate current research directions.
The supervision of industrial processes requires the exchange of information in real time between users and control systems.
Users may be moving around a working area and need to consult information to supervise a particular process. Therefore, it
is important to study the characteristics and stability of the paths to determine which services can be offered. In this paper,
the effect of mobility on duration and stability of the links in an ad hoc network is analysed using stochastic activity networks.
The ad hoc network is made up of six mobile nodes where the routing protocol is AODV. This study shows the path average lifetime
which enables the evaluation of which type of services can be offered by the network.
The integration of ad-hoc networks into real environments is now becoming more and more common and supervision and control systems are no exception. The efficiency of the communication in these networks as well as various other factors, are governed by the working area, the number of nodes, mobility, transmission power, etc. In this paper, the mobility and reachability of mobile nodes appearing spontaneously in a large installation such as can be found in a water purification system are studied. These nodes form an ad-hoc network and communicate between each other in order to finally reach a fixed node which can offer them information from the rest of the system in real time or act as a gateway to other remote networks. The study was done analytically using stochastic activity models, and using the minimum number of nodes necessary to successfully serve a water purification system with a high percentage of communication cover
The existing work on dependability modelling and analysis of networks have main focuses on the, structural properties. However, the communication networks also have dynamic characteristics and behavioral properties, such as changes of topology, routes, and traffic loads, which should necessarily be reflected in the modelling. We regard the dependability modelling and analysis of IP networks with an intra-domain routing and traffic handling. This yields to an increased complexity in the modelling and analysis, due to the increase of the state space. Several techniques have been proposed to deal with the growth of the state space. To an analyst, an interesting point is, whether he/she can make a trade-off to the factors under consideration, i.e. the model representativeness vs. modelling complexity, and computation efforts vs. result accuracy. To meet these requirements, we propose a modelling approach where failures and repairs of network components as well as routing and traffic handling are described by a set of stochastic activity networks (SAN). The SANs are designed to restrict the generation of the state space to the most probable states, which enables an analysis without creation of an excessively large state space and achieving a sufficient accuracy of the result. A case study based on the Norwegian university IP backbone network demonstrates the applicability of this approach
Mobile ad-hoc network (MANET) technology is an essential piece in the path towards a ubiquitous Internet. MANET routing protocol parameter configuration should be further analyzed since it may significantly impact network performance. In this paper, we perform tests in real MANET environments using the ad-hoc on-demand distance vector (AODV) routing protocol. We study the influence of the protocol, the implementation and a set of AODV link maintenance mechanisms parameter values on network performance, suggesting that usage of different settings from those proposed by default increase reactivity after topology changes with small impact on bandwidth and power consumption in a set of scenarios
Wireless mesh networks (WMNs) consist of mesh routers and mesh clients, where mesh routers have minimal mobility and form the backbone of WMNs. They provide network access for both mesh and conventional clients. The integration of WMNs with other networks such as the Internet, cellular, IEEE 802.11, IEEE 802.15, IEEE 802.16, sensor networks, etc., can be accomplished through the gateway and bridging functions in the mesh routers. Mesh clients can be either stationary or mobile, and can form a client mesh network among themselves and with mesh routers. WMNs are anticipated to resolve the limitations and to significantly improve the performance of ad hoc networks, wireless local area networks (WLANs), wireless personal area networks (WPANs), and wireless metropolitan area networks (WMANs). They are undergoing rapid progress and inspiring numerous deployments. WMNs will deliver wireless services for a large variety of applications in personal, local, campus, and metropolitan areas. Despite recent advances in wireless mesh networking, many research challenges remain in all protocol layers. This paper presents a detailed study on recent advances and open research issues in WMNs. System architectures and applications of WMNs are described, followed by discussing the critical factors influencing protocol design. Theoretical network capacity and the state-of-the-art protocols for WMNs are explored with an objective to point out a number of open research issues. Finally, testbeds, industrial practice, and current standard activities related to WMNs are highlighted.
Mobile radio systems beyond 3G will comprise one-hop and multihop communication. Analytically derived performance results indicate a potential capacity gain when introducing multihop communication. In this paper a novel resource allocation scheme is presented that beneficially exploits these potentials of relaying by means of concurrent resource scheduling under control of a central station. However, whether multihop communication can be advantageously deployed strongly depends on parameters like noise power, interference, selected modulation and coding scheme, attenuation, and distance between source and destination. These dependencies will be demonstrated by means of analytical performance evaluations taking into account link-level simulations.
Present basis of knowledge management is the efficient share of information. The challenges that modern industrial processes have to face are multimedia information gathering and system integration, through large investments and adopting new technologies. Driven by a notable commercial interest, wireless networks like GSM or IEEE 802.11 are now the focus of industrial attention, because they provide numerous benefits, such as low cost, fast deployment and the ability to develop new applications. However, wireless nets must satisfy industrial requisites: scalability, flexibility, high availability, immunity to interference, security and many others that are crucial in hazardous and noisy environments. This paper presents a thorough survey of all this requirements, reviews the existing wireless solutions, and explores possible matching between industry and the current existing wireless standards.
The 1990s have seen a rapid growth of research interests in mobile ad hoc networking. The infrastructureless and the dynamic nature of these networks demands new set of networking strategies to be implemented in order to provide efficient end-to-end communication. This, along with the diverse application of these networks in many different scenarios such as battlefield and disaster recovery, have seen MANETs being researched by many different organisations and institutes. MANETs employ the traditional TCP/IP structure to provide end-to-end communication between nodes. However, due to their mobility and the limited resource in wireless networks, each layer in the TCP/IP model require redefinition or modifications to function efficiently in MANETs. One interesting research area in MANET is routing. Routing in the MANETs is a challenging task and has received a tremendous amount of attention from researches. This has led to development of many different routing protocols for MANETs, and each author of each proposed protocol argues that the strategy proposed provides an improvement over a number of different strategies considered in the literature for a given network scenario. Therefore, it is quite difficult to determine which protocols may perform best under a number of different network scenarios, such as increasing node density and traffic. In this paper, we provide an overview of a wide range of routing protocols proposed in the literature. We also provide a performance comparison of all routing protocols and suggest which protocols may perform best in large networks.
A highly dynamic topology is a distinguishing feature and challenge of a mobile ad hoc network. Links between nodes are created and broken, as the nodes move within the network. This node mobility affects not only the source and/or destination, as in a conventional wireless network, but also intermediate nodes, due to the network’s multihop nature. The resulting routes can be extremely volatile, making successful ad hoc routing dependent on efficiently reacting to these topology changes.In order to better understand this environment, a number of characteristics have been studied concerning the links and routes that make up an ad hoc network. Several network parameters are examined, including number of nodes, network dimensions, and radio transmission range, as well as mobility parameters for maximum speed and wait times. In addition to suggesting guidelines for the evaluation of ad hoc networks, the results reveal several properties that should be considered in the design and optimization of MANET protocols.
We propose a new protocol, named DS-SWAN (Differentiated Services-Stateless Wireless Ad Hoc Networks), to support end-to-end Quality of Service (QoS) in ad hoc networks connected to a fixed DiffServ domain. When congestion is excessive for the correct functioning of real-time applications, DS-SWAN determines the source of the problem, warns the nodes in the ad hoc network if it is the case and the nodes react by slowing down best-effort traffic. Furthermore, we present an associated routing protocol for the ad hoc network in this context, named SD-AODV (Service Differentiation-Ad Hoc On-Demand Distance Vector), where new route requests are suppressed at certain nodes to maintain the desired QoS requirements for real-time flows. A simulation study is presented for the case when traffic is sent from the ad hoc network towards the fixed network as well as in the opposite direction. The scalability of DS-SWAN with respect to the network size, number of real-time traffic sources, node mobility and best-effort traffic load is analyzed. Simulation results indicate that DS-SWAN and SD-AODV significantly improve end-to-end delays and jitter for real-time flows without starvation of background traffic.
Model-based evaluation of computer systems and networks is an increasingly important activity. For modeling to be used effectively, software environments are needed that ease model specification, construction, and solution. Easy to use, graphical methods for model specification that support solution of families of models with differing parameter values are also needed. Since no model solution technique is ideal for all situations, multiple analysis and simulation-based solution techniques should be supported. This paper describes UltraSAN, one such software environment. The design of UltraSAN reflects its two main purposes: to facilitate the evaluation of realistic computer systems and networks, and to provide a test-bed for investigating new modeling techniques. In UltraSAN, models are specified using stochastic activity networks, a stochastic variant of Petri nets, using a graphical X-Window based interface that supports large-scale model specification, construction, and solution. Models may be parameterized to reduce the effort required to solve families of models, and a variety of analysis and simulation-based solution techniques are supported. The package has a modular organization that makes it easy to add new construction and solution techniques as they become available. In addition to describing the features, capabilities, and organization of UltraSAN, the paper illustrates the use of the package in the solution for the unreliability of a fault-tolerant multiprocessor using two solution techniques.
Routing in ad hoc networks is a complicated task because of many reasons. The nodes are low-memory, low-powered, and they cannot maintain routing tables large enough for well-known routing protocols. Because of that, greedy forwarding at intermediate nodes is desirable in ad hoc networks. Also, for traffic engineering, multi-path capabilities are important. So, it is desirable to define routes at the source like in source based routing (SBR) while performing greedy forwarding at intermediate nodes.We investigate trajectory-based routing (TBR) which was proposed as a middle-ground between SBR and greedy forwarding techniques. In TBR, source encodes trajectory to be traversed and embeds it into each packet. Upon the arrival of each packet, intermediate nodes decode the trajectory and employ greedy forwarding techniques such that the packet follows its trajectory as much as possible.In this paper, we address various issues regarding implementation of TBR. We also provide techniques to efficiently forward packets along a trajectory defined as a parametric curve. We use the well-known Bezier parametric curve for encoding trajectories into packets at source. Based on this trajectory encoding, we develop and evaluate various greedy forwarding algorithms
Different communication alternatives that form an Heterogeneous Network for a Supervision and Control System of the purification network of a large city are evaluated in order to determine their viability for the supervision and control of the system. In addition there is a study of which offers the best services and costs for different scenarios. Four communication alternatives (which assure a 100% geographic cover of the stations) for the interconnection of the Remote Station and the Central Station are analysed, all of which are situated in the metropolitan area of a large city: point-to-point connections over ISDN (Integrated Services Digital Network), Virtual Private Networks VPNs/IP over ISDN, VPN over ADSL (Asymmetric Digital Subscriber Line) and wireless link 802.11. For the communication between the Central Station and the mobile remote clients, the connection via GPRS (General Packet Radio Service) and the connection by means of UMTS (Universal Mobile Telecommunication System) are evaluated. For the measurements and posterior analysis, control information and images have been transmitted. The viability of these types of solutions in the proposed scenarios is shown and the costs involved in each solution are analysed.
In 1997, IEEE standardized the physical layers and the medium access for wireless local area networks. This paper presents a performance study of the distributed coordination function, the fundamental contention-based access mechanism. Most performance studies adopt unchecked simplifying assumptions or do not reveal all details of the simulation model. We develop a stochastic Petri net model, which captures all relevant system aspects in a concise way. Simulation allows to quantify the influence of many mandatory features of the standard on performance, especially the backoff procedure, extended interframe spaces, and the timing synchronization function. We identify conditions when simplifying assumptions commonly used in analytical modeling are justified. Applying these conditions, we derive a more compact and analytically tractable model from the detailed model.
The use of VAN infrastructures to give support to applications in the traditional areas of industrial networks , and in particular in applications with MAN requirements, as can be found in building automation, or the case studied here; utilities network control, is viable but with limitations. The use of wireless networks such as WiMAX allows proprietary networks to be quickly set up at low cost. In spite of this potential, the burst behavior they sometimes display means that the applications must take this into consideration. Thus, the control links in the VAN nodes must be based only on local information within the VAN node, using the VAN infrastructure to improve the working of a global system. Although WiMAX can form part of this VAN infrastructure in a utilities network control application and satisfy the requirements of these applications, it is important to take into consideration the interference produced in the ISM spectrum, such as the fading effects produced in wireless communication, which may produce breaks and lack of availability. These possible problems must be foreseen and considered for the higher levels of the applications so that they do not affect the performance of the system. The need to avoid congestion in the channels and the fact that the channel bandwidths change at times due to variations of the SNR mean that it is necessary to use dynamic bandwidth management mechanisms. The mechanisms must avoid congestion in the cannel, both in the normal working of the system, as well as during moments when there is degradation in the cannel and the consequent loss of bandwidth that this degradation causes.
Mobile Ad-Hoc Network (MANET) has become an increasingly active research area with a plethora of work in ad-hoc routing, media access, and protocols, etc. However, much of the effort so far has been in simulation with only a few systems that have ever been implemented and none that we know have been tried in a scale beyond a dozen nodes. One reason is the high complexity involved in implementing and testing actual ad-hoc networks, and the lack of software tools for doing so. We have thus built an inexpensive and flexible environment to support such tasks and to facilitate network research. The core component is a mobility emulator to test an ad-hoc network of virtually any scale and with any mobility scenario without actually moving the nodes physically.