Rosanna Manzo

Packet Flow on Telecommunication Networks

The aim of this paper is to introduce a macroscopic fluid dynamic model dealing with the flow of information on a telecommunication network encoded in packets. Taking an intermediate time and space scale, we propose a model similar to that introduced recently for car traffic; see [G. M. Coclite, M. Garavello, and B. Piccoli, SIAM J. Math. Anal., 36 (2005), pp. 1862–1886]. For dynamics at nodes we consider two “routing algorithms” and prove existence of solutions to Cauchy problems. The main difference among the two algorithms is the possibility of redirecting packets of the second algorithm, which in turn implies stability, i.e., Lipschitz continuous dependence on initial data, not granted for solutions using the first algorithm.

A fluid dynamic model for supply chains

The paper deals with a fluid dynamic model for supply chains. A mixed continuum-discrete model is proposed and possible choices of solutions at nodes guaranteeing the conservation of fluxes are discussed. Fixing a rule a Riemann solver is defined and existence of solutions to Cauchy problems is proved.

A continuum-discrete model for supply chains dynamics

This paper is focused on continuum-discrete models for supply chains. In particular, we consider the model introduced in [10], where a system of conservation laws describe the evolution of the supply chain status on sub-chains, while at some nodes solutions are determined by Riemann solvers. Fixing the rule of flux maximization, two new Riemann Solvers are defined. We study the equilibria of the resulting dynamics, moreover some numerical experiments on sample supply chains are reported. We provide also a comparison, both of equilibria and experiments, with the model of [15].

Hybrid optimal control: Case study of a car with gears

The purpose of this paper is to show the use of some analytical tools for hybrid optimal control. We illustrate both the hybrid maximum principle and the hybrid necessary principle at work on a simple example of a car with gears. The model is sufficiently rich to generate non-trivial optimization problems and the obtained results match with intuition. Finally, computer simulations confirm the theoretical analysis.

A FLUID DYNAMIC MODEL FOR TELECOMMUNICATION NETWORKS WITH SOURCES AND DESTINATIONS

This paper proposes a macroscopic fluid dynamic model dealing with the flows of information on a telecommunication network with sources and destinations. The model consists of a conservation law for the packet density and a semilinear equation for traffic distribution functions, i.e., functions describing packet paths. We describe methods to solve Riemann problems at junctions assigning different traffic distribution functions and two “routing algorithms.” Moreover, we prove the existence of solutions to Cauchy problems for small perturbations of network equilibria.

Numerical Schemes for the Optimal Input Flow of a Supply Chain

An innovative numerical technique is presented to adjust the inflow to a supply chain in order to achieve a desired outflow, reducing the costs of inventory or the goods timing in warehouses. The supply chain is modeled by a conservation law for the density of processed parts coupled to an ODE for the queue buffer occupancy. The control problem is stated as the minimization of a cost functional

Analysis of the multi-server Markov queuing system with unlimited buffer and negative customers

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Optimal distribution of traffic flows in emergency cases

measuring the queue size and the quadratic difference between the outflow and the expected one. The main novelty is the extensive use of generalized tangent vectors to a piecewise constant control, which represent time shifts of discontinuity points. Such a method allows convergence results and error estimates for an upwind-Euler steepest descent algorithm, which is also tested by numerical simulations.

Single server retrial queue with group admission of customers

Consideration was given to the multi-server queuing system with unlimited buffer, Markov input flow, and Markov (general) process of servicing all customers on servers with the number of process states and intensities of the inter-phase passage depending on the number of customers in the system. Additionally, a Markov flow of negative customers arrives to the system, the arriving negative customer killing the last queued positive customer. A recurrent algorithm to calculate the stationary probabilities of system states was obtained, and a method of calculation of the stationary distribution of the waiting time before starting servicing of a positive customer was proposed.

ON RELAXATION OF STATE CONSTRAINED OPTIMAL CONTROL PROBLEM FOR A PDE-ODE MODEL OF SUPPLY CHAINS

The aim of this work is to present a technique for the optimisation of emergency vehicles travel times on assigned paths when critical situations, such as car accidents, occur. Using a fluid-dynamic model for the description of car density evolution, the attention is focused on a decentralised approach reducing to simple junctions with two incoming roads and two outgoing ones (junctions of 2 × 2 type). We assume the redirection of cars at junctions is possible and choose a cost functional that describes the asymptotic average velocity of emergency vehicles. Fixing an incoming road and an outgoing road for the emergency vehicle, we determine the local distribution coefficients that maximise such functional at a single junction. Then we use the local optimal coefficients at each node of the network. The overall traffic evolution is studied via simulations, both for simple junctions or cascade networks, evaluating global performances when optimal parameters on the network are used.