Exit Nodes Research Articles

An alternative method for refined process structure trees (RPST)

PurposeThe refined process structure tree (RPST), the hierarchy of non-overlapping single-entry single-exit (SESE) regions of a process model, has been utilized for better comprehension and more efficient analysis of business process models. Existing RPST methods, based on the triconnected components of edges, fail to identify a certain type of SESE region. The purpose of this paper is to introduce an alternative method for generating a complete RPST utilizing rather simple techniques.Design/methodology/approachThe proposed method first focuses on the SESE regions of bonds and rigids, from the innermost ones to the outermost ones, utilizing dominance and post-dominance relations. Then, any SESE region of a series nested in a bond or a rigid is identified with a depth-first search variation. Two-phase algorithms and their completeness proofs, a software tool incorporating visualization of stepwise outcomes, and the experimental results of the proposed method are provided.FindingsThe proposed method utilizes simple techniques that allow their straightforward implementation. Visualization of stepwise outcomes helps process analysts to understand the proposed method and the SESE regions. Experiments with 604 SAP reference models demonstrated the limitation of the existing RPST methods. The proposed method, however, completely identified all types of SESE regions, defined with nodes, in less computation time than with the old methods.Originality/valueEach triconnected component of the undirected version of a process model is associated with a pair of boundary nodes without discriminating between the entry and the exit. Here, each non-atomic SESE region is associated with two distinct entry and exit nodes from the original model in the form of a directed graph. By specifying the properties of SESE regions in more comprehensible ways, this paper facilitates a deeper understanding of SESE regions rather than relying on the resulting RPST.

Bookings in the European gas market: characterisation of feasibility and computational complexity results

As a consequence of the liberalisation of the European gas market in the last decades, gas trading and transport have been decoupled. At the core of this decoupling are so-called bookings and nominations. Bookings are special long-term capacity right contracts that guarantee that a specified amount of gas can be supplied or withdrawn at certain entry or exit nodes of the network. These supplies and withdrawals are nominated at the day-ahead. The special property of bookings then is that they need to be feasible, i.e., every nomination that complies with the given bookings can be transported. While checking the feasibility of a nomination can typically be done by solving a mixed-integer nonlinear feasibility problem, the verification of feasibility of a set of bookings is much harder. The reason is the robust nature of feasibility of bookings-namely that for a set of bookings to be feasible, all compliant nominations, i.e., infinitely many, need to be checked for feasibility. In this paper, we consider the question of how to verify the feasibility of given bookings for a number of special cases. For our physics model we impose a steady-state potential-based flow model and disregard controllable network elements. For this case we derive a characterisation of feasible bookings, which is then used to show that the problem is in coNP for the general case but can be solved in polynomial time for linear potential-based flow models. Moreover, we present a dynamic programming approach for deciding the feasibility of a booking in tree-shaped networks even for nonlinear flow models. It turns out that the hardness of the problem mainly depends on the combination of the chosen physics model as well as the specific network structure under consideration. Thus, we give an overview over all settings for which the hardness of the problem is known and finally present a list of open problems.

Sensor-based gas tracking

The propagation of information encoded in the fluctuations of chemical species of natural gas transported within natural gas distribution grids allows for a new gas tracking method. In contrast to state of the art gas and calorific value tracking based on numerical gas-flow simulations, the presented method is solely based on signal processing techniques. Due to a wider diversification of natural gas sources, gas and therefore calorific value tracking is of great interest for gas grid operators to provide fair invoicing of gas customers. The calorific value of substitute natural gas, e.g. produced by biogas or power-to-gas plants, injected concurrently into natural gas grids, typically deviates significantly over time in comparison to the prevailing natural gas in the grid. Sampling gas features like the chemical species contained in injected gases, or the standard density, by means of calibrated sensors, e.g. by process gas chromatography or infrared sensors, provides time-dependent signals that can be taken for calorific value extrapolation from source nodes to downstream nodes. To that end, we provide a general estimation of gas feature related transmission characteristics of natural gas distribution grids based on a straightforward one-dimensional diffusion model. Additionally, we present an accurate technique to estimate transit times and source fractions on gas grid exit nodes. We show with a field experiment, that gas tracking based on gas sensor signals is feasible and that our new method improves on state of the art gas tracking software based on computational fluid dynamics, already in use for gas customer invoicing.

A multilevel model of the European entry-exit gas market

In entry-exit gas markets as they are currently implemented in Europe, network constraints do not affect market interaction beyond the technical capacities determined by the TSO that restrict the quantities individual firms can trade at the market. It is an up to now unanswered question to what extent existing network capacity remains unused in an entry-exit design and to what extent feasible adjustments of the market design could alleviate inefficiencies. In this paper, we offer a four-level modeling framework that is capable of analyzing these issues and provide some first results on the model structure. In order to decouple gas trading from network congestion management, the TSO is required to determine technical capacities and corresponding booking fees at every entry and exit node up front. Firms book those capacities, which gives them the right to charge or discharge an amount of gas at a certain node up to this capacity in every scenario. Beyond these technical capacities and the resulting bookings, gas trade is unaffected by network constraints. The technical capacities have to ensure that transportation of traded quantities is always feasible. We assume that the TSO is regulated and determines technical capacities, fees, and transportation costs under a welfare objective. As a first step we moreover assume perfect competition among gas traders and show that the booking and nomination decisions can be analyzed in a single level. We prove that this aggregated model has a unique solution. We also show that the TSO’s decisions can be subsumed in one level as well. If so, the model boils down to a mixed-integer nonlinear bilevel problem with robust aspects. In addition, we provide a first-best benchmark that allows to assess welfare losses that occur in an entry-exit system. Our approach provides a generic framework to analyze various aspects in the context of semi-liberalized gas markets. Therefore, we finally discuss and provide guidance on how to include several important aspects into the approach, such as network and production capacity investment, uncertain data, market power, and intra-day trading.

A Multilevel Model of the European Entry-Exit Gas Market

In entry-exit gas markets as they are currently implemented in Europe, network constraints do not affect market interaction beyond the technical capacities determined by the TSO that restrict the quantities individual firms can trade at the market. It is an up to now unanswered question to what extent existing network capacity remains unused in an entry-exit design and to what extent feasible adjustments of the market design could alleviate inefficiencies. In this paper, we offer a four-level modeling framework that is capable of analyzing these issues and provide some first results on the model structure. In order to decouple gas trading from network congestion management, the TSO is required to determine technical capacities and corresponding booking fees at every entry and exit node up front. Firms book those capacities, which gives them the right to charge or discharge an amount of gas at a certain node up to this capacity in every scenario. Beyond these technical capacities and the resulting bookings, gas trade is unaffected by network constraints. The technical capacities have to ensure that transportation of traded quantities is always feasible. We assume that the TSO is regulated and determines technical capacities, fees, and transportation costs under a welfare objective. As a first step we moreover assume perfect competition among gas traders and show that the booking and nomination decisions can be analyzed in a single level. We prove that this aggregated model has a unique solution. We also show that the TSO's decisions can be subsumed in one level as well. If so, the model boils down to a mixed-integer nonlinear bilevel problem with robust aspects. In addition, we provide a first-best benchmark that allows to assess welfare losses that occur in an entry-exit system. Our approach provides a generic framework to analyze various aspects in the context of semi-liberalized gas markets. Therefore, we finally discuss and provide guidance on how to include several important aspects into the approach, such as network and production capacity investment, uncertain data, market power, and intra-day trading.

Hierarchic Entropy: An Information Theoretic Measure of Evolutionary Robotic Behavioral Diversity

This paper investigates the design of information theoretic-based fitness function for embedded evolutionary robotics (ERs). Such fitness relies on the assumption that interesting behaviors result in a high sensorimotor (individual) diversity. The current simple entropy as a diversity metric only considers individuals’ difference but ignores their spatial relationship. The sensorimotor stream can be analyzed to construct a simple directed graph that has unique entry and exit nodes. This paper proposes a hierarchic entropy as a diversity metric by incorporating the simple entropy and the spatial relationship based graph entropy. Maximizing the hierarchic entropy, achieved by on-board evolutionary algorithm, thus defines a self-driven fitness function enforcing the controller visiting diverse sensorimotor states. The proposed algorithm achieves better performance than the published results of other entropy-based methods only relying on simple entropy, without requiring additional computational resources.

Pursuit of a moving target with bounded speed on a directed acyclic graph under partial information

Abstract The optimal control of a ‘blind’ airborne pursuer searching for an evader moving on a road network with positive bounded speed toward a set of goal vertices is considered. To aid the pursuer and provide feedback information, certain roads in the network have been instrumented with unattended ground sensors (UGSs) that detect evader motion. When the pursuer arrives at an instrumented node, the UGS therein informs the pursuer if and when the evader visited the node. The pursuer is aware of the bounds on the evader’s speed. Moreover, the embedded graph with the UGSs as vertices and connecting roads as edges is restricted to be a directed acyclic graph (DAG). At time $0$, the evader’s entry into the road network is registered at UGS $1$, the entry node. The pursuer also arrives at the entry node after some delay $d>0$ and is thus informed about the presence of the intruder/evader in the network, whereupon the chase is on. Capture entails the pursuer and evader being co-located at an UGS location. However, if the evader reaches an exit node of the graph without being captured, it is deemed to have escaped. We compute the maximum initial delay $d$ and the ensuing pursuit policy, for which capture is guaranteed.

Evacuation time estimate for total pedestrian evacuation using a queuing network model and volunteered geographic information.

Estimating city evacuation time is a nontrivial problem due to the interaction between thousands of individual agents, giving rise to various collective phenomena, such as bottleneck formation, intermittent flow, and stop-and-go waves. We present a mean field approach to draw relationships between road network spatial attributes, the number of evacuees, and the resultant evacuation time estimate (ETE). Using volunteered geographic information, we divide 50 United Kingdom cities into a total of 704 catchment areas (CAs) which we define as an area where all agents share the same nearest exit node. 90% of the agents are within ≈6,847 m of CA exit nodes with ≈13,778 agents/CA. We establish a characteristic flow rate from catchment area attributes (population, distance to exit node, and exit node width) and a mean flow rate in a free-flow regime by simulating total evacuations using an agent based "queuing network" model. We use these variables to determine a relationship between catchment area attributes and resultant ETEs. This relationship could enable emergency planners to make a rapid appraisal of evacuation strategies and help support decisions in the run up to a crisis.

How Anonymous Is the Tor Network? A Long-Term Black-Box Investigation

A popular choice for anonymous Internet communication, the Tor network uses entry, relay, and exit nodes to hide the traffic's origin. However, an investigation that involved running real applications and website requests through Tor revealed numerous agglomerations of exiting traffic that an attacker could exploit.

Tor does not stink: Use and abuse of the Tor anonymity network from the perspective of law

Tor is one of the most popular technical means of anonymising one's identity and location online. While it has been around for more than a decade, it is only in recent years that Tor has begun appearing in mainstream media and openly catching the attention of governments and private citizens alike. The conflicting interests related to the use and abuse of Tor also raise a number of legal issues that are yet to be analysed in depth in academic literature. This article focuses on a number of relevant legal issues pertaining to Tor and reflects our initial legal comments, while noting that all of the identified legal questions merit further research.After introducing the technical side of Tor and the attitudes of governments towards it, we (1) explore the human rights connotations of the anonymity provided by Tor, coming to the conclusion that this anonymity is an integral part of certain human rights, particularly the right to privacy and the right to freedom of expression. Government activities with respect to Tor should thus not be unlimited. In relation to this, we (2) provide a closer look at the problem of content liability of the Tor exit node operators. Finally, we (3) point out several legal problems in conducting criminal investigations with the need to obtain the evidence from the Tor network.We conduct this legal analysis in the context of international and European law, paying a particular attention to the case law of the European Court of Human Rights and the Court of Justice of the European Union.

Convex reformulations for solving a nonlinear network design problem

We consider a nonlinear nonconvex network design problem that arises, for example, in natural gas or water transmission networks. Given is such a network with active and passive components, that is, valves, compressors, control valves (active) and pipelines (passive), and a desired amount of flow at certain specified entry and exit nodes in the network. The active elements are associated with costs when used. Besides flow conservation constraints in the nodes, the flow must fulfill nonlinear nonconvex pressure loss constraints on the arcs subject to potential values (i.e., pressure levels) in both end nodes of each arc. The problem is to compute a cost minimal setting of the active components and numerical values for the flow and node potentials. We examine different (convex) relaxations for a subproblem of the design problem and benefit from them within a branch-and-bound approach. We compare different approaches based on nonlinear optimization numerically on a set of test instances.

General displacement arch-cantilever element method for stress analysis of arch dam

Based on the general displacement method and the basic hypothesis of the trial load method, a new advanced trial load method, the general displacement arch-cantilever element method, was proposed to derive the transformation relation of displacements and loads between the surface nodes and middle plane nodes. This method considers the nodes on upstream and downstream surfaces of the arch dam to be exit nodes (master nodes), and the middle plane nodes to be slave nodes. According to the derived displacement and load transformation matrices, the equilibrium equation treating the displacement of middle plane nodes as a basic unknown variable is transformed into one that treats the displacement of upstream and downstream nodes as a basic unknown variable. Because the surface nodes have only three degrees of freedom (DOF), this method can be directly coupled with the finite element method (FEM), which is used for foundation simulation to analyze the stress of the arch dam with consideration of dam-foundation interaction. Moreover, using the FEM, the nodal load of the arch dam can be easily obtained. Case studies of a typical cylindrical arch dam and the Wudongde arch dam demonstrate the robustness and feasibility of the proposed method.

Detection and analysis of eavesdropping in anonymous communication networks

Anonymous communication networks, like Tor, partially protect the confidentiality of user traffic by encrypting all communications within the overlay network. However, when the relayed traffic reaches the boundaries of the network, toward its destination, the original user traffic is inevitably exposed to the final node on the path. As a result, users transmitting sensitive data, like authentication credentials, over such networks, risk having their data intercepted and exposed, unless end-to-end encryption is used. Eavesdropping can be performed by malicious or compromised relay nodes, as well as any rogue network entity on the path toward the actual destination. Furthermore, end-to-end encryption does not assure defense against man-in-the-middle attacks. In this work, we explore the use of decoys at multiple levels for the detection of traffic interception by malicious nodes of proxy-based anonymous communication systems. Our approach relies on the injection of traffic that exposes bait credentials for decoy services requiring user authentication, and URLs to seemingly sensitive decoy documents which, when opened, invoke scripts alerting about being accessed. Our aim was to entice prospective eavesdroppers to access our decoy servers and decoy documents, using the snooped credentials and URLs. We have deployed our prototype implementation in the Tor network using decoy IMAP, SMTP, and HTTP servers. During the course of over 30 months, our system has detected 18 cases of traffic eavesdropping that involved 14 different Tor exit nodes.

Radio Frequency Based Emergency Exit Node Technology

This paper introduces an indoor sensor fusion wireless communication device which provides the Location Based Service (LBS) using fire prevention facility. The proposed system can provide information in real time by optimizing the hardware of Wi-Fi technology. The proposed system can be applied to a fire prevention facility (i.e., emergency exit) and provide information such as escape way, emergency exit location, and accident alarm to smart phone users, dedicated terminal holders, or other related organizations including guardians, which makes them respond instantly with lifesaving, emergency mobilization, etc. Also, the proposed system can be used as a composite fire detection sensor node with additional fire and motion detect sensors.

Extended Nymble: Method for Tracking Misbehaving Users Anonymosly While Blocking

We have many of anonymizing networks which provide users to access services of server anonymously. Anonymity has received increasing attention in the literature due to user awareness of their privacy. Nowadays, anonymity provides protection to users to enjoy network services without being traced. Anonymizing networks such as Tor allow users to access Internet services privately by using a series of routers to hide the client's IP address from the server. Web site administrators routinely rely on IPaddress blocking for disabling access to misbehaving users, but blocking IP addresses is not practical if the abuser routes through an anonymizing network. As a result, administrators block all known exit nodes of anonymizing networks, denying anonymous access to misbehaving and behaving users alike. To address this problem Nymble is developed, a system in which servers can misbehaving users. We present extensions to nymble framework for anonymizing blacklisting schemes. First, we provide a mechanism to nymble manager to track blacklisting of user in multiple linking windows while preserving anonymity of the users. Some users always look to misbehave with servers; there major intention is to make the server down. The problem with nymble is nymble manager blacklist a user for one likability window (i.e. 1 day), on the other day again he can misbehave with same server or other server. He can continue it as his everyday activity as Nymble manager doesn't have any mechanism to identify such type of users while preserving anonymity. To address this problem, we present a method which can identify such users, while preserving anonymity and nymble manager with identified information can decide upon how much time to blacklist a misbehaving user. We also suggest some algorithms which are changed in comparison to existing nymble.

Blacklisting Misbehaving Users for Enhancing Security in Anonymizing Networks

Anonymizing networks such as Tor allow users to access Internet services privately by using a series of routers to hide the client's IP address from the server. The success of such networks, however, has been limited by users employing this anonymity for abusive purposes such as defacing popular Web sites. Web site administrators routinely rely on IP-address blocking for disabling access to misbehaving users, but blocking IP addresses is not practical if the abuser routes through an anonymizing network. As a result, administrators block all known exit nodes of anonymizing networks, denying anonymous access to misbehaving and behaving users alike. To address this problem, we present Nymble, a system in which servers can misbehaving users, thereby blocking users without compromising their anonymity. Our system is thus agnostic to different servers' definitions of misbehavior—servers can blacklist users for whatever reason, and the privacy of blacklisted users is maintained. Nymble is a system in which servers can misbehaving users, thereby blocking users without compromising their anonymity and the privacy of blacklisted users is maintained. Web site administrators routinely rely on IP-address blocking for disabling access to misbehaving users, but blocking IP addresses is not practical if the abuser routes through an anonymizing network. As a result, administrators block all known exit nodes of anonymizing networks, denying anonymous access to misbehaving and behaving users alike.

A Survey on Privacy Preserving Technique for Blocking Misbehaviors in Anonymous Networks

Anonymizing networks such as Tor allow users to access internet services privately by using a series of routers to hide the client’s IP address from the server. The success of such networks However has been limited by users employing this anonymity for abusive purposes such as defacing popular web sites. Web site administrators routinely rely on IP-address for blocking or disabling access to misbehaving users, but blocking IP addresses is not practical if the abuser routes through an IP addresses is not practical if the abuser routes through an anonymizing network. As a result, administrators block all known exit nodes of anonymizing networks, denying anonymous access misbehaving and behaving users alike. To address this problem, we present Nymble, a system in which servers can “blacklist” misbehaving users, thereby blocking users without compromising their anonymity. Our system is thus agnostic to different server definitions of misbehavior servers can blacklist users for whatever reason, and the privacy of blacklisted users is maintained.

Review on Attack and Defense in Tor

Tor is currently the most famous tool of anonymous TCP communications for clients who need security, privacy and anonymity in their low-latency communications over the public network such as Internet. For this purpose, Tor provides reliable ways of communication through randomly selecting relay network circuits on client’s request to offer a secure communication path. However, several research papers are available which identify weaknesses of Tor that attackers can exploit to reveal a client’s identity. This paper highlights a few such Tor’s weaknesses through which attackers can launch snooping attacks on Tor. Some major attacks are discussed and it is observed that most attacks are launched at application-level protocols such as HTTP after compromising exit node or both entry and exit nodes of Tor relay circuits. Countermeasures against such attacks are also identified to increase security and anonymity over Tor based communications.

Nymble Blocking System

In order to allow users to access Internet services privately, anonymizing networks like Tor uses a series of routers to hide the client’s IP address from the server. These networks, however, have been marred by users employing this anonymity for abusive purposes such as defacing popular web sites. Usually, web site administrators rely on IP-address blocking in order to disable access to misbehaving users, but it is impractical if the abuser routes through an anonymizing network. In order to avoid this, administrators bar all known exit nodes of the anonymizing network, thereby denying anonymous access to all the users (whether misbehaving or not). To solve this issue, we introduce Nymble, a system where servers blacklist misbehaving users, thereby blocking users without affecting their anonymity. Nymble is thus agnostic to varied definitions of misbehavior. Servers can block users for any reason, and the privacy of blacklisted users is not affected in any case.

HYBRID TRAINING METHOD OF ARTIFICIAL NEURAL NETWORK ON THE BASIS OF THE MODIFIED ANT ALGORITHM

Back propagation of error algorithm is one of the training methods of artificial neural network. Its creation gave an additional incitement to the development of artificial neural network theory. An increase and appearance of the new tasks had led to the appearance of hybrid algorithms based on classical and stochastic ones. They emphasize the advantages and decrease the drawbacks of each other. The article suggests the hybrid training algorithm of neural network based on the ant colony and back propagation of error algorithms. The ant colony algorithm is used to choose the priority ways of moving along the neural network and to change the network balance with the help of pheromones. In comparison with the basic algorithm the ant colony one is changed. Instead of distance records between each pair of connected nodes and total network error records, they use the record of error value on the each exit node at the end of each ant travel. In the modified algorithm, each network weight changes the coefficient with the glance of the value of pheromone matrix elements, the error on the each node of exit layer and suggested function for pheromone accounting. The algorithm performance was checked on the famous databases [http://archive.ics.uci.edu/ml/]. The results of the experiments show that in comparison with another algorithm the modified one accelerates the training of neural network. The algorithm implementation was approved on the Microsoft SQL Server 2005 in Analysis Services. It will help to apply suggested algorithm to solve another problems of classification.