Sasa Klampfer

Impact of P2P traffic on IP communication networks’ performances

Over recent years there has been a large increase in the use of P2P (peer- to-peer) applications around the world. These applications have become very popular today and there are a lot of new users every day. Increasing of P2P users has a very great impact on increasing P2P traffic in communications networks. In this paper we pay attention to measuring of P2P traffic, by analyzing and simulating these kinds of network traffic. The estimated parameters of the measured traffic in analysis were used for modeling such traffic in a simulation tool, where we show how P2P traffic has an impact on IP communication networkspsila performances. For this reason we built a test network in OPNET simulation tool where users, in addition to classical applications, also use P2P applications. We modeled the custom application which is based on the measurement of P2P traffic for a normal user.

A system for the expert analysis of tactical networks’ performances

The simulation of tactical networks is an important task in the process of military missions planning. Such methodologies assure a higher probability of success for tactically critical operations on military fields. The manual analysis of simulation results is a very time-consuming task and requires expert knowledge to correctly interpret these results. This paper briefly defines those concepts of an expert system also used in the design of our system for automatic expert analysis regarding those simulations results obtained by an OPNET modeler. It presents some analyses algorithms which we have developed for tactical network evaluation. The more important parameters that evaluate tactical networks are: transmitter bandwidth utilization, traffic delays, message completion rates and radio visibility. The functionalities and implementation of a developed expert system are also described in the context of the whole system for simulating tactical networks.

Mathematical analysis of routing, based on circular graphs

Routing is a problem domain with an infinite number of end-solutions. One possible approach is to solve such problems using of graph theory. This paper presents a mathematical analysis for a routing problem, based on circular graphs, where the focus is on searching for the shortest path on a circular graph. The theoretical section will be argued by an example where we look for the fastest path and possible walks within specified circular graph.

Modeling of call server occupancy: A case study

The article presents problems of modeling and designing the necessary and adequate capacity of the call server input connections for serving the calls into the system. The main aim of the research work is to find the optimum number of input server connections while minimizing the number of rejected requests according to a specific maximum number of expected calls in a specific time interval, i.e. at a peak hour. Model is based on key segments composing the call and severs system (ordinary, lamer and dummy caller model, Gaussian distribution of calls, mechanisms of accepting and rejecting calls, management of input connection capacity, random call triggering, etc.). Using them in simulator gives a way to find an optimal solution or manually or automatically by automated simulation runs with incrementing/decrementing the number of input connections into the system. The article also presents an automatic analysis of simulation runs and a statistical final report, which includes a conclusion on the results obtained in different scenarios.

Expert System for Automatic Analysis of Results of Network Simulation

The simulation of communication networks is an important task in the process of network planning and optimization processes. Such methodologies assure a higher probability for networks to operate successfully under different critical conditions, which are difficult or unpractical to be tested in the real networks. Typical applications of such simulations are the simulation of military tactical radio networks. The manual analyses of network simulation results, is a very time-consuming task and requires expert knowledge to correctly interpret such results. This is a good motivation to develop the system for automatic analysis with expert knowledge, which will ease the process of mission planning and training. For such needs, we have developed the simulation methodology and tools, supported by the expert system, which are going to be presented in detail within this chapter. During this chapter, we will briefly introduce expert systems (further ES), Command and Control Information Systems used in NATO and known solutions to simulate such systems. The ES is defined as an intelligent computer program with a certain level of expert knowledge, which using procedures to solve exactly specified problems. All definitions for expert systems, in many books, are quite similar, and they describe the way such system includes a rigid range of expert (specialized) knowledge or research domain. Within this area, it is capable of creating intelligent decisions. This is some kind of imitation, where a system tries to capture behavior of skills. Using the acquired knowledge; a system can analyze input/output information, solve problems, and utilize utensil decisions within the problem domain. From this point of view, these systems cannot solve all kinds of problems, but they can solve well-known and deduced problems. It is stated in one of the references that expert systems are based on knowledge (Hart, 1998, pg. 7), respectively on an information handler base. Classification by Sauter places an expert system on the right side of the straight line, where we can find systems, which handle information. Expert systems are closely related to artificial intelligence methods. As a rule, they share quality and quantity information, probability theory, fuzzy set theory, and a number of arithmetic and logic rules, based on heuristic expectations.

Influences of Classical and Hybrid Queuing Mechanisms on VoIP's QoS Properties

Nowadays we can find many TCP/IP based network applications, such as: WWW, e-mail, video-conferencing, VoIP, remote accesses, telnet, p2p file sharing, etc. All mentioned applications became popular because of fast-spreading broadband internet technologies, like xDSL, DOCSIS, FTTH, etc. Some of the applications, such as VoIP (Voice over Internet Protocol) and video-conferencing, are more time-sensitive in delivery of network traffic than others, and need to be treated specially. This special treatment of the time-sensitive applications is one of the main topics of this chapter. It includes methodologies for providing a proper quality of service (QoS) for VoIP traffic within networks. Normally, their efficiency is intensively tested with simulations before implementation. In the last few years, the use of simulation tools in R&D of communication technologies has rapidly risen, mostly because of higher network complexity. The internet is expanding on a daily basis, and the number of network infrastructure components is rapidly increasing. Routers are most commonly used to interconnect different networks. One of their tasks is to keep the proper quality of service level. The leading network equipment manufacturers, such as Cisco Systems, provide on their routers mechanisms for reliable transfer of time-sensitive applications from one network segment to another. In case of VoIP the requirement is to deliver packets in less than 150ms. This limit is set to a level where a human ear cannot recognize variations in voice quality. This is one of the main reasons why leading network equipment manufacturers implement the QoS functionality into their solutions. QoS is a very complex and comprehensive system which belongs to the area of priority congestions management. It is implemented by using different queuing mechanisms, which take care of arranging traffic into waiting queues. Time-sensitive traffic should have maximum possible priority provided. However, if a proper queuing mechanism (FIFO, CQ, WFQ, etc.) is not used, the priority loses its initial meaning. It is also a well-known fact that all elements with memory capability involve additional delays during data transfer from one network segment to another, so a proper queuing mechanism and a proper buffer length should be used, or the VoIP quality will deteriorate. If we take a look at the router, as a basic element of network equipment, we can realise that we are dealing with application priorities on the lowest level. Such level is presented by waiting queues and queuing mechanisms, related with the input traffic connection interface.

Location and visualization of the communication problems in a simulated Slovenian Armed Forces tactical radio network

The article presents a concept of design, using the methods of simulation results, automatic analysis, and taking into account expert knowledge, and visualization of communication problems in the developed Tactical Player. The main emphasis is on the segment of simulation results evaluation on the basis of fuzzy sets, from which we have developed rules, the combination of which is used for evaluation of the quality of communication parameters between tactical radio stations. A special note should also be taken of the concept of modeling a tactical radio network and its characteristics, the mode of communication between radio stations, hierarchic organization, the problems of manual analysis of simulation results, etc. We present our solution for automatic analysis and the solution for visualization of problematic segments in the course of communication. The reader is acquainted with the problems of wireless communications and the key parameters influencing the connection between communicating entities, such as radio visibility, message transfer success, packet loss, deterioration of the signal–noise relation, etc. Because visualization of problematic time frames of the simulated communication on a virtual simulation field directly depends on the automatic analysis precision, we also used mathematical procedures (probability theory and possibility theory) as the basis of the fuzzy logic used. For a better understanding of the modeled prototype’s functioning, we also include a block scheme in the form of a process scheme, on the basis of which we can show the segments that are new and are a scientific contribution in the field of simulation techniques.