Design and analysis of a denial-of-service-resistant quality-of-service signaling protocol for MANETs

Quality-of-service (QoS) signaling protocols for mobile ad hoc networks (MANETs) are highly vulnerable to attacks. In particular, a class of denial-of-service (DoS) attacks can severely cripple network performance with relatively little effort expended by the attacker. A distributed QoS signaling protocol that is resistant to a class of DoS attacks on signaling is proposed. The signaling protocol provides QoS for real-time traffic and employs mechanisms at the medium access control (MAC) layer, which serve to avoid potential attacks on network resource usage. The key MAC layer mechanisms that provide support for the QoS signaling scheme include sensing of available bandwidth, traffic policing, and rate monitoring, all of which are performed in a distributed manner by the mobile nodes. The proposed signaling scheme achieves a compromise between signaling protocols that require the maintenance of per-flow state and those that are completely stateless. The signaling scheme scales gracefully in terms of the number of nodes and/or traffic flows in the MANET. The authors analyze the security properties of the protocol and present simulation results to demonstrate its resistance to DoS attacks.     

Byzantine robust trust establishment for mobile ad hoc networks

In a mobile ad hoc network (MANET), the nodes act both as traffic sources and as relays that forward packets from other nodes along multi-hop routes to the destination. Such networks are suited to situations in which a wireless infrastructure is unavailable, infeasible, or prohibitively expensive. However, the lack of a secure, trusted infrastructure in such networks make secure and reliable packet delivery very challenging. A given node acting as a relay may exhibit Byzantine behavior with respect to packet forwarding, i.e., arbitrary, deviant behavior, which disrupts packet transmission in the network. For example, a Byzantine node may arbitrarily choose to drop or misroute a certain percentage of the packets that are passed to it for forwarding to the next hop. In earlier work, we proposed a trust establishment framework, called Hermes, which enables a given node to determine the “trustworthiness” of other nodes with respect to reliable packet delivery by combining first-hand trust information obtained independently of other nodes and second-hand trust information obtained via recommendations from other nodes. A deficiency of the Hermes scheme is that a node can fail to detect certain types of Byzantine behavior, such as packet misforwarding directed at a particular source node. In this paper, we propose new mechanisms to make Hermes robust to Byzantine behavior and introduce a punishment policy that discourages selfish node behavior. We present simulation results that demonstrate the effectiveness of the proposed scheme in a variety of scenarios involving Byzantine nodes that are malicious both with respect to packet forwarding and trust propagation.     

On optimal position control of mechanisms in rolling processes

The paper deals with a feedback system created with the use of the method of regular synthesis of optimal control system which should bring a non-linear and discontinuous planar object to a moving target in a minimum time. In real, practical circumstances, on this system there impinge perturbations such as unexpected and undefined motion resistances variations, parameter changes and errors in measurements of states, which cause that the created time-optimal closed-loop system may generate limit-cycles and may be stopped in other state than the required final one (target). There is shown that while using adequately so called F-solution of discontinuous differential equation, the synthesised closed-loop system may become insensitive towards above mentioned perturbations. Some suggestions are made as to practical application in position devices in reversing rolling mills     

Switching curve deformation in a time-optimal closed-loop system

The dynamics of a closed-loop system resulting from the solution of a time-optimal problem of a two-dimensional differential inclusion are discussed. It is shown that internal uncertainties (such as variations in resistances or parameter changes) cause trajectories of the closed-loop motion to (1) spiral convergently around the target and reach it in a finite time; (2) spiral divergently around the target and reach a limit curve; and (3) reach the target in a finite time in a sliding mode. Some suggestion for practical applications are given     

Shearing optimization of the rolled billet according to a minimum waste criterion

The purpose of this paper is to resolve the control problem of shearing a rolled billet. The appropriate control should result in shearing each section to a length which consists of a predetermined basic length and a tolerance. The control should be effected with the minimum waste criterion. Because the final length of the rolled billet to be cut is not known, the control is based on the prediction of this length. The prediction procedure as well as the static and dynamic process optimization is given in the paper.     

On the sensitivity of a time-optimal positional control

A second-order differential equation with a discontinuous and nonlinear right-hand side has been taken as the model for positional mechanisms. This model covers a large class of motion resistances, particularly all types of friction. Sensitivity of time-optimal positional control to motion resistances and switching function variations has been investigated. This correspondence also contains some suggestions for practical control structure synthesis. Numerical examples help to illustrate the theoretical analysis.