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Performance Evaluation of Two-Link Multirate Loss Models with Restricted Accessibility

Keramidi Irene P., Moscholios Ioannis D., Sarigiannidis Panagiotis G., Logothetis Michael D.

Journal of Telecommunications and Information Technology

2020

nr 2

61--69

We consider a two-link communication system with restricted accessibility that services Poisson arriving calls of many service-classes and propose a multirate teletraﬃc loss model for its analysis. In a restricted accessibility system, call blocking occurs even if available resources do exist at the time of a call’s arrival. In the two-link system under consideration, each link has two thresholds (oﬄoading and support) which express the in-service calls in a link. The oﬄoading threshold represents the point from which a link oﬄoads calls. The support threshold (which is lower than the oﬄoading threshold) deﬁnes the point up to which a link supports oﬄoaded calls. The two-link system with restricted accessibility is modeled as a loss system whose steady state probabilities do not have a product form solution. However, approximate formulas for the determination of call blocking probabilities are proposed. In addition, we also provide a corresponding analysis related to the case of quasi-random traﬃc (i.e. traﬃc generated by a ﬁnite number of users). The accuracy of all formulas is veriﬁed through simulation and is found to be quite satisfactory.

Critical infrastructure preparedness : cascading of disruptions considering vulnerability and Dependency

Eid M., Hakkarainen T., Terhi K., Souza-Cursi-de E., El-Hami A.

Journal of Polish Safety and Reliability Association

2016

Vol. 7, No. 1

61--66

Critical Infrastructures’ disruptions may result in crises of unacceptable outcomes in modern societies. Thus, it is important to develop models that allow describing CIs’ disruptions and their propagation characteristics. CI disruptions depend on both the type of the threat and on the nature of the CIs’ mutual dependencies. A model describing the cascade of disruptions should, then, be able to consider the CI-threat vulnerability and the CI-CI dependency. The paper presents a model where cascades are exactly described using an integral equation. The integral equation admits an analytical solution if the occurrence probability distribution functions (pdf) of the disruptions obey Stochastic Poisson Processes (SPP). The introduction of the “vulnerability to the threat” and the “CIs’ (inter)dependencies” is carried out with the help of time constant factors called: “vulnerability strain factor” and “disruption strain factor”, respectively. An academic case is presented in order to demonstrate the applicability of the model and illustrate some interesting features of the model. A complete set of numerical applications will be published separately.

Derivatives of Blocking Probabilities in Multirate Access Tree Networks

Moscholios I. D., Vardakas J. S., Logothetis M. D., Boucouvalas A. C.

Advances in Electronics and Telecommunications

2013

Vol. 3, no. 5

38--48

We consider a multirate access tree network accommodating service-classes of Poisson traffic, and focus on the determination of derivatives of Call Blocking Probabilities (CBP) with respect to offered traffic-load of any service-class. Based on the derivatives, we further show how we can successfully approximate CBP for small variations of offered traffic-load.