Routing Behavior Research Articles

Correction to "Lattice Networks: Capacity Limits, Optimal Routing, and Queueing Behavior"

Correction to "Lattice Networks: Capacity Limits, Optimal Routing, and Queueing Behavior"

Explanation of Performance Degradation in Turn Model

The Turn model routing algorithms for mesh interconnection network achieve partial adaptivity without any virtual channels. However, the routing performance measured by simulations is worse than with the simple deterministic routing algorithm. Authors have explained these results simply by uneven dynamic load through the network. However, this phenomenon has not been studied further. This paper investigates performance degradation with Turn model and drawbacks of partially adaptive routing in comparison with the deterministic routing, and it introduces some new concepts. Our simulations deal with individual channels and results are presented by 3D graphs, rather than by commonly used averages. An additional parameter--channel occupation, which is consistent with queuing theory commonly used in many proposed analytical models, is introduced. We also propose a new structure, the Channel Directions Dependency Graph (CDDG). It provides a new approach in analysis, helps in understanding of dynamic routing behaviour, and it can be generalized in other routing algorithms.

Evolution of spatial cognition: mechanisms and tasks

Finding places and orienting in space are among the most basic behavioral performances of all mobile animals. In many different species, simple mechanisms have been identified for recognizing places, returning to a “home” after an excursion, or concatenating simple navigational steps to longer routes. These mechanisms form the basis of human spatial performances. The talk will explore the relation between animal and human spatial cognition along two dimensions, (1) animal roots of human performances, and (2) features of spatial cognition uniquely found in humans. In the first part of the talk, we will present a novel behavioral paradigm for studying large-scale spatial performances in rats (Holscher in J Exp Biol 208:561–569, 2005). The setup consists of a running ball in a socket, hovering in a stream of air. The rat is fixated over the pole of the ball such that the rat’s legs touch the ball. Translatory movements of the rat are thus transformed into rotations of the ball about horizontal (“equatorial”) axes. Rotations of the rat about its vertical (dorso-ventral) axis are not restricted while the ball is prevented from such rotations by guiding wheels. In effect, then, the system is open-loop for translations and closed-loop for rotations of the rat. The rotation of the ball is measured by an optical system and used to control a virtual reality projection surrounding the rat on a panoramic screen. Initial results indicate that rats accept the virtual environment and run for long distances, up to several hundreds of meters. In addition, they can be trained to search for rewards at places specified by landmarks. In ongoing experiments, we investigate route behavior in rats, which is considered a stepping stone to topological navigation in humans. In the second part of the talk, we will discuss in what ways human spatial abilities differs from animal performances. We suggest that human spatial behavior, while relying on abilities found already in the animal wayfinding hierarchy (Trullier et al. in Prog Neurobiol 51:483–544, 1997), has taken advantage of two trends of the cognitive evolution in the social domain. First, communicating spatial knowledge, either face-to-face, by publishing or by sign-posting enables us to travel to almost every point in the world with a minimum of prior knowledge. Second, cooperative behavior in building cities, roads, and transportation systems shapes the environment in ways that may be more easy to navigate. We will argue that human wayfinding differs from animal behavior in the ability of utilizing these “socio-spatial” types of knowledge. The cognitive apparatus needed for these performances is not specifically spatial, but includes general problem solving and working memory abilities.

Transport Protocols in the TCP Paradigm and their Performance

This paper defines a class of "TCP-like" transport protocols, called protocols in the TCP Paradigm. The name indicates the protocols are not TCP, but in some sense similar to it. The class includes TCP and also Tom Kelly's "Scalable TCP", and more. Most of the protocols in the class require ECN in order to become implementable. Most even require a form of ECN that allows a high rate of marked packets. The paper analyzes performance of protocols in the TCP Paradigm and indicates a subset that is likely to perform as well as, or quite possibly better than, Scalable TCP. Criteria are the ability to achieve high throughput, to maintain a steady flow if the ECN marking probability is constant, and to adapt quickly to a changing marking probability. A main conclusion is that in order to benefit from protocols in this paradigm, "source behavior" (reaction of endpoints to marked and unmarked packets) and "router behavior" (how routers choose marking probabilities) must be investigated together.

Networks with Advance Reservations: Applications, Architecture, and Performance

In general, two types of resource reservations in computer networks can be distinguished: immediate reservations which are made in a just-in-time manner and advance reservations, i.e., the reservation of resources a long time before they are actually used. Advance reservations are essential for Grid computing but can also be useful for a variety of other applications that require network quality-of-service (QoS), such as content distribution networks with large amounts of content that must be distributed among the servers in a timely fashion. With the emerged MPLS standard and its explicit routing features, it is possible to overcome the unpredictable routing behavior which has so far prevented the implementation of advance reservation services. In this paper, additional opportunities are described that arise for network operators and customers with the implementation of advance reservations in computer networks. This includes the search for suitable transmission intervals or transmission rates. Furthermore, network operators can use the additional knowledge about future network status in order to improve the performance of the network. This paper discusses these issues and describes the software architecture of a management system that implements the previously mentioned services and optimization mechanisms. The paper is complemented with a performance evaluation of the management architecture, focused on the benefit for clients and operators.

Toward the design of robust interdomain routing protocols

The border gateway protocol, the interdomain routing protocol for the Internet, allows for a wide variety of routing policies that may interact in unintended and unstable ways. Recent work on BGP and related protocols has begun to incorporate formal protocol models, which have enabled rigorous descriptive analyses of BGP. More recently, such models have been used to give prescriptive guidelines for the design of new protocols. These guidelines include both sufficient conditions for good routing behavior and limitations on what can be achieved without coordination between routers. Here we review potential routing problems, various formal protocol models, and the design guidelines they have been used to prove.

An internet routing forensics framework for discovering rules of abnormal BGP events

Abnormal BGP events such as attacks, misconfigurations, electricity failures, can cause anomalous or pathological routing behavior at either global level or prefix level, and thus must be detected in their early stages. Instead of using ad hoc methods to analyze BGP data, in this paper we introduce an Internet Routing Forensics framework to systematically process BGP routing data, discover rules of abnormal BGP events, and apply these rules to detect the occurrences of these events. In particular, we leverage data mining techniques to train the framework to learn rules of abnormal BGP events, and our results from two case studies show that these rules are effective. In one case study, rules of worm events discovered from the BGP data during the outbreaks of the CodeRed and Nimda worms were able to successfully detect worm impact on BGP when an independent worm, the Slammer, subsequently occurred. Similarly, in another case study, rules of electricity blackout events obtained using BGP data from the 2003 East Coast blackout were able to detect the BGP impact from the Florida blackout caused by Hurricane Frances in 2004.

Using Feedback in Collaborative Reinforcement Learning to Adaptively Optimize MANET Routing

Designers face many system optimization problems when building distributed systems. Traditionally, designers have relied on optimization techniques that require either prior knowledge or centrally managed runtime knowledge of the system's environment, but such techniques are not viable in dynamic networks where topology, resource, and node availability are subject to frequent and unpredictable change. To address this problem, we propose collaborative reinforcement learning (CRL) as a technique that enables groups of reinforcement learning agents to solve system optimization problems online in dynamic, decentralized networks. We evaluate an implementation of CRL in a routing protocol for mobile ad hoc networks, called SAMPLE. Simulation results show how feedback in the selection of links by routing agents enables SAMPLE to adapt and optimize its routing behavior to varying network conditions and properties, resulting in optimization of network throughput. In the experiments, SAMPLE displays emergent properties such as traffic flows that exploit stable routes and reroute around areas of wireless interference or congestion. SAMPLE is an example of a complex adaptive distributed system.

Empirical Validation of Wireless Models in Simulations of Ad Hoc Routing Protocols

Computer simulation has been used extensively as an effective tool in the design and evaluation of systems. One should not, however, underestimate the importance of validation—the process of ensuring whether a simulation model is an appropriate representation of the real-world system. Validation of wireless network simulations is difficult due to strong interdependencies among protocols at different layers and uncertainty in the wireless environment. The authors present an approach of coupling direct-execution simulation and traces from real outdoor experiments to validating simple wireless models that are used commonly in simulations of wireless ad hoc networks. This article documents a common testbed that supports direct execution of a set of ad hoc routing protocol implementations in a wireless network simulator. By comparing routing behavior measured in the real experiment with behavior computed by the simulation, the authors validate the models of radio behavior upon which protocol behavior depends.

Oxidative chemistry of 2-nitro and 4-nitroestradiol: Dichotomous behavior of radical intermediates and novel potential routes for oxyfunctionalization and B-ring fission of steroidal scaffolds

Oxidation of 4-nitro-17β-estradiol ( 1) with the peroxidase/H 2O 2 system gave the symmetric C 2-linked dimer ( 3) through phenoxy radical coupling. Similar oxidation of 2-nitro-17β-estradiol ( 2), in which the nitro group is coplanar with the aromatic ring, yielded 9α- and 9β-hydroxy-2-nitro-17β-estradiol ( 4a, b), (17β)-2-nitroestra-1(10),2,4,9(11)-tetraene-3,17-diol ( 5), and (12α,17β)-2-nitroestra-1(10),2,4,9(11)-tetraene-3,12,17-triol ( 6). With higher concentrations of H 2O 2, the novel secoestra-1(10),2,4-trien-9-one derivative 7 was obtained from 2. Theoretical calculations suggested that the peculiar behavior of 2 may be due to the generation of a relatively stable radical intermediate at C 9, which would then be converted to the reactive quinone methide 8. The chemistry described in this paper appears to be an intriguing example of control of the site of substitution over evolution of phenoxy radicals, and opens new vistas toward selective oxyfunctionalization of the estrane skeleton.

Cost Benefit Analysis for Urban Policy Measures Related to Economic Transport

This paper discusses the application of urban freight transport decision-support tools in cost benefit analyses (CBA). The principles of the CBA are based on the Microeconomic Theory. It is supposed that individuals optimise their benefits and, therefore, a single policy measure can have a certain influence on the whole consumption pattern. When the effects of a policy measure on the situation of companies are assessed in the framework of a CBA, a cost minimising can be supposed, and adaptations of the individual companies could be modelled by the application of optimisation tools. The difference between the cost situation before and after the realisation of a policy measure could thereby be determined. As an example, the adaptation changes in routing behaviour in the urban goods distribution will be discussed. It is shown that adaptations in the routing can absorb parts of the costs resulting from a lorry ban on certain urban streets. Guidelines for the use of optimisation tools for company modelling are deduced. Behaviour reactions of economic transport actors and methods for their assessment are analysed. For the covering abstract see ITRD E129315.

Locating internet routing instabilities

This paper presents a methodology for identifying the autonomous system (or systems) responsible when a routing change is observed and propagated by BGP. The origin of such a routing instability is deduced by examining and correlating BGP updates for many prefixes gathered at many observation points. Although interpreting BGP updates can be perplexing, we find that we can pinpoint the origin to either a single AS or a session between two ASes in most cases. We verify our methodology in two phases. First, we perform simulations on an AS topology derived from actual BGP updates using routing policies that are compatible with inferred peering/customer/provider relationships. In these simulations, in which network and router behavior are "ideal", we inject inter-AS link failures and demonstrate that our methodology can effectively identify most origins of instability. We then develop several heuristics to cope with the limitations of the actual BGP update propagation process and monitoring infrastructure, and apply our methodology and evaluation techniques to actual BGP updates gathered at hundreds of observation points. This approach of relying on data from BGP simulations as well as from measurements enables us to evaluate the inference quality achieved by our approach under ideal situations and how it is correlated with the actual quality and the number of observation points.

Improved Solution Algorithm for Multicommodity Continuous Distribution and Assignment Model

Consider a city, with multiple regional activity centers (RACs), in which the locations of traveler demand are continually dispersed. The total demand generated from a particular location in the city is fixed, but the demands from this location to the RACs are subject to a distribution function with respect to the relative transportation cost to each RAC. We take into account the cost of transportation in characterizing travelers’ choices. The congestion effect is explicitly built into the model by using a flow- and location-dependent transportation cost function. The routing behavior of travelers in the city and the user equilibrium choices of RACs are modeled by constructing a spatial user equilibrium flow pattern. The problem is formulated as a combined distribution and assignment model. A solution algorithm that is improvement upon a previously adopted iterative algorithm between the distribution function for the choice of RAC and a mixed finite-element method for route choices is proposed to solve the resultant continuous problem. A numerical example is given to demonstrate the superiority of the improved algorithm.

A core stateless bandwidth broker architecture for scalable support of guaranteed services

We present a novel bandwidth broker architecture for scalable support of guaranteed services that decouples the QoS control plane from the packet forwarding plane. More specifically, under this architecture, core routers do not maintain any QoS reservation states, whether per-flow or aggregate. Instead, the QoS reservation states are stored at and managed by a bandwidth broker. There are several advantages of such a bandwidth broker architecture. Among others, it avoids the problem of inconsistent QoS states faced by the conventional hop-by-hop, distributed admission control approach. Furthermore, it allows us to design efficient admission control algorithms without incurring any overhead at core routers. The proposed bandwidth broker architecture is designed based on a core stateless virtual time reference system developed recently. This virtual time reference system provides a unifying framework to characterize, in terms of their abilities to support delay guarantees, both the per-hop behaviors of core routers and the end-to-end properties of their concatenation. We focus on the design of efficient admission control algorithms under the proposed bandwidth broker architecture. We consider both per-flow end-to-end guaranteed delay services and class-based guaranteed delay services with flow aggregation. Using our bandwidth broker architecture, we demonstrate how admission control can be done on a per domain basis instead of on a hop-by-hop basis. Such an approach may significantly reduce the complexity of the admission control algorithms. In designing class-based admission control algorithms, we investigate the problem of dynamic flow aggregation in providing guaranteed delay services and devise a new apparatus to effectively circumvent this problem. We conduct detailed analyses to provide theoretical underpinning for our schemes as well as to establish their correctness. Simulations are also performed to demonstrate the efficacy of our schemes.

New lower and upper bounds for the competitive ratio of transmission protocols

Transmission protocols like TCP are usually divided into a time scheduling and a data selection policy. We consider on-line algorithms of data selection policies for any time scheduling policy and any routing behavior in a network. For the model introduced by Adler et al. [Proc. 5th Israel Symp. on Theory of Computing Systems, 1997, pp. 64–72], we improve both the lower and the upper bound on the competitive ratio making them asymptotically tight. Furthermore, we present a lower bound that depends on the size of the buffers that are available both to the sender and to the receiver. We obtain a constant lower bound for the competitive ratio for constant buffer size.

架橋下通航における操船者の行動に関する研究-I : 操船行動のモデル化

架橋下通航における操船者の行動に関する研究-I : 操船行動のモデル化

Using adaptive routing to achieve Quality of Service

Self-monitoring allows a network to observe its own behavior via probing and measurement mechanisms. This can then be exploited by the system to take autonomous decisions for the purpose of system management, performance management and user Quality of Service (QoS). In this paper, we experimentally explore how QoS goals that are externally set by network users, can then be explicitly exploited by a self-aware network to control its own behavior to attain these goals. The experiments we report are conducted in two distinct Cognitive Packet Network (CPN) test-beds which use probing to select the routes which best satisfy the QoS goal. Our experiments validate this concept with QoS goals which include end-to-end delay, packet loss, and a mixture of these two metrics. We observe that using only delay in the QoS goal is a good way to reduce delay and loss if losses result only from congestion. However, using loss in the QoS goal is seen to be useful if the paths that are adaptively selected avoid nodes where packet losses occur for reasons other than congestion. In general we observe that CPN networks effectively adapt routing behavior to the QoS goal that is specified.

On the effect of location inaccuracy on geographic face routing in wireless networks

Geographic routing protocols [1], [5], [6]) are very( attractive choices for routing in wireless networks for several reasons. First, such protocols incur low route discovery overhead relative to flooding-based approaches, and hence conserve energy and bandwidth. Second, these protocols are stateless in the sense that nodes need not maintain per-destination nformation, and only neighbor locationi information is needed to route packets. In mobile networks with frequent topology changes, geographic routing can find new routes quickly by using only local topology information. For these reasons, geographic routing is expected to become the protocol of choice for many applications in wireless networks, for example in sensor networks it is proposed for data-centric storage [7] and distributed indexing [2]. Hence, it is quite crucial to develop a detailed understanding of the behavior of geographic routing for various practical settings and to evaluate its performance and (more importantly) its correctness in those settings. Most geographic routing protocols use greedy forwarding as its basic mode of operation, where the next forwarding hop is chosen to minimize the distance to the destination. Greedy forwarding, however, fails in the presence of

Benefits of traffic engineering using QoS routing schemes and network controls

We demonstrate the benefits of traffic engineering by studying three realistic network models derived from an actual service provider network. We evaluate traffic engineering in the presence of QoS-based routing schemes compared with Destination-Based Routing, the default routing behavior for the Internet. We also simulate prioritization of important traffic flows by implementing priority in one or more of the path caching, path ordering, and actual route selection phases of the constraint-based routing framework. We observe that traffic engineering can provide 20–50% network capacity savings. We also observe that prioritization in more than one phase of constraint-based routing can provide even more significant benefits.

Realistic bus route model considering the capacity of the bus

This paper investigates the bus route behavior using a more realistic cellular automaton model in which the bus capacity is considered. It is shown that with the introduction of bus capacity, four new states appear compared with the previous works. The results enable us to conclude that the efficiency of the bus route system cannot be enhanced simply through increasing the number of buses. Moreover, it is pointed out that a proper value of the bus capacity can lead to the optimal configuration of the bus system.