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Članek opisuje metode analize in zasnovo sistema za avtomatizirano analizo simulacijskih rezultatov pridobljenih iz orodja za simulacije komunikacijskih omrežij - OPNET modelerja. Pri tem smo se omejili na temeljne gradnike, ki jih sistem mora vsebovati, da ga lahko uvrstimo v razred ekspertnih sistemov. V prvem delu članka smo za vsak gradnik podali temeljit opis. Dodali smo tudi opise mehanizmov mehkih množic, baze znanja in pravil, ki se uporabljajo v procedurah sklepanja in iskanja koncnih rešitev. V drugem delu članka predstavljamo ekspertni sistem, ki smo ga zasnovali za analizo rezultatov simulacij taktičnih radijskih omrežij. V nadaljevanju je opisana funkcionalnost sistema, metode analize, posameznih komunikacijskih parametrov in načini podajanja rezultatov.

Simulations of telecommunications networks have become very important tools for their evaluation. A very important influence in simulations has network traffic. This paper introduces new concepts for the modeling of measured network traffic in simulation tools. With these new concepts, we can improve descriptions of the random packet-size process, especially for maximal-packets of network traffic, which have a very great impact on the bit or packet rates of network traffic. The suggested methods improve the contents of packets, especially maximal packets in modeled network traffic simulations, which leads to smaller differences in bit and packet-rates between measured and modeled network traffics. Simulacije telekomunikacijskih omrežij postajajo pomembno orodje za ovrednotenje le teh. Zelo pomemben in velik vpliv v simulacijah ima tudi omrežni promet. Ta članek predstavlja novi koncept modeliranja izmerjenega omrežnega prometa v simulacijskih orodjih. Z tem novim konceptom lahko izboljšamo opis naključnega procesa velikosti paketov omrežnega prometa, zlasti maksimalnih paketov, kateri imajo zelo velik vpliv na srednjo vrednost celotnega prometa v bitih in paketih na časovno enoto. Predlagane metode izboljšajo opis vsebnosti paketov v omrežnem prometu, še posebej maksimalnih paketov v modeliranem prometu, kar posledično vodi do manjših razlik v srednji vrednosti bitov in paketov na časovno enoto med izmerjenim in modeliranim prometom.

Now days the use of mobile communications, applications and mobile data transfer are rapidly increased. The standardization work of GSM-based systems has begun in the 1980s, when the developing of unique radio communications system for Europe, at 900MHz, has started. Since then many modifications have been made in order to fulfill the increasing demand from the operators and cellular users. This paper describes a Universal Mobile Telecommunications Service (UMTS) network and an example of data reception, when web application and voice over internet protocol (VoIP) are used. The UMTS represent third generation (3G), broadband packet based transmission of text, video, digitized voice and multimedia at data rates up to 2 megabits per second (Mbps). The UMTS is intention for consistent set of services to mobile computers and phone users, no matter where they are located in the world. Third generation technology is based on the Global System for Mobile (GSM) communication standard. It is also endorsed by major standards, bodies and manufacturers, as the planned standard for mobile users around the world. Because UMTS is today fully available, computers and phone users can be constantly attached to the internet wherever they are, wherever they travel and as they roam, will have exactly the same set of capabilities. Users will have access through a combination wireless and satellite transmissions. Even today, some places are not fully covered with UMTS, so in that case, users can use multimode devices that switch to the currently available technology, such as GSM 900 and 1800 where UMTS is not yet available. UMTS offers many different applications like: light and heavy web browsing, reading web mail, VoIP quality speech, video conferencing, base access, telnet session, file transfer, file copy, GSM and PCM quality speech, SMS, MMS and so on. We pick out only two applications, and that is light web browsing and VoIP, which are today very popular for most population on the world, because many applications allow user to connect with the whole world at any place and any time. Under the third generation partnership project (3GPP) the third generation of UMTS cellular system was developed. The main parts of this systems are UMTS terrestrial radio access network (UTRAN), based on wide division multiple access (WCDMA) radio technology and GSM/EDGE radio access network (GERAN) based on global system for mobile telecommunications (GSM/enhanced data rates for global evolution (EDGE) radio technology). On the other hand the UMTS can be divided into three major parts: User Equipment (UE) that interfaces with the user and radio interface, UTRAN that handles all radio-related functionality, and the Core Network (CN), which is responsible for switching and routing calls and data connections to external networks. These elements are shown in Fig. 1. In second section the base UMTS elements and their function are presented on Fig. 2 and Fig. 3. Section 3 shortly represents the capabilities of the Opnet Modeler program and describes types of networks, which can be simulated. Section 4 represents the construction of UMTS network in the Opnet Modeler and describes the web application and VoIP. The web browsing is simulated in UMTS network application and object response time and page response time were observed. We located UMTS mobile node with name ,Web2- near UMTS transmitter. If we compare positions for both nodes (Fig. 4), is very simple to say, that is node,,Web2- closer to transmitter than node,,Webl,,. Both nodes are placed on fix position and both have identical parameters and identical settings, because of that, we can simply estimate remote distance influence at interdependence with object response time and page response time. Results of the simulations are shown on Fig. 5-6 and 8-9. Fig. 7 shows us UMTS structure for VoIP application. Section 5 concludes the paper. Članek opisuje posamezne gradnike omrežja UMTS (Universal Mobile Telecommunication System), in njegovo simulacijo s programom Opnet Modeler. V fazi simuliranja omrežja se bomo omejili na dejavnike, ki vplivajo na kakovost posamezne storitve (aplikacije), predvsem pa na vpliv oddaljenosti in kvaliteto sprejema. Slednjo smo ovrednotili s pomočjo odzivnih časov pri spletni aplikaciji in telefoniji IP (ang. Internet Protocol).

Last year's CachneLogic research shows that, in January 2006, P2P traffic accounted for approximately 71% of all internet traffic, and was the main reason for internet traffic increasing. Figure 1 shows the trend of P2P traffic increase. The pioneer of P2P file sharing applications is very well-known Napster, which was created in 1999 by Shawn Fanning and used for sharing music files. Napster was finally destroyed by the music industry after Court proceedings. Napster, as a concept, had a great influence on developing file-sharing applications, such as eMula, Kazza, pTorrent, UmeWire, Skype etc. In our research, we paid attention to the modeling of network traffic caused by P2P file sharing applications (P2P traffic). We measured P2P traffic using the Wireshark network traffic capture tool as shown in Figure 2. We created a self-similarity and long-range dependence analysis for the measured tests P2P traffics, the results of which are shown in Table 1, and in Figures 3 and 4. We also estimated the parameters for a statistical description of a P2P network separately for the processes of packet-size and inter-arrival time, which represent the main network traffic processes. The histogram method for distribution parameters' estimation is shown in Figure 5. These estimated distribution parameters were used for modeling a customized application of P2P network traffic in OPNET simulation tool. Using simulations with simple test networks, as shown in Figure 6, we represented the possibilities of simulating the impact of P2P network traffic on network performances. We show how the volume of P2P users impacts on other applications' performances (web time response shown in Figure 7 and link utilization shown in Figure 8.) V zadnjih letih doživlja delež prometa, ki ga ustvarjajo P2P aplikacije za izmenjavo datotek skokovito rast. S svojo količino in intenzivnostjo znatno vpliva na zmogljivost omrežij. Namen članka je predstavitev metode za analizo in modeliranje takšnega prometa za potrebe simulacij. Na osnovi izmerjenega prometa smo ocenili statistične parametre za modeliranje tovrstnega prometa. V simulacijskem okolju OPNET smo zgradili testno omrežje, kjer se pretakajo poleg ostalih prometov še promet aplikacij P2P, ki smo ga modelirali s predlagano metodo. S simulacijami smo preučili vpliv P2P prometa na zmogljivost omrežja.

An approach to the computer-aided measurement of static characteristics is described. There are two basic criteria for choosing the number of measurement points: the speed of measurement performance and the continuity of the measured characteristic, which are contradictory. The approach is based on the adaptive method for choosing a limited set of measuring points with a uniform distribution along the characteristic, without the need for apriori knowledge about measured parts, limited by maximum permitted power, current and voltage. The approach is implemented as Virtual Instrument (VI) using LabView from national Instruments. The results of experimental of statical characteristics of different types of electronic elements, such as resistor zener diode, transistor and trystor, confirm the efficiency of the presented method even in the case of choosing a relatively small number of measurement points (10-15). V članku opisujemo računalniško podprt postopek določanja statičnih l - U karakteristik elektronskih elementov. Osnovna kriterija izbire števila merilnih točk na karakteristiki sta hitrost meritve in zveznost izmerjene karakteristike, ki pa sta protislovna. Postopek temelji na adaptivni metodi izbiranja omejenega števila maksimalne merilnih točk tako, da so enakomerno razporejene po kakrakteristiki, brez vnaprejšnjega poznavanja lastnosti merjenca, ob omejitvah dovoljene moči, toka in napetosti. Realiziran je v obliki virtualnega instrumenta v programskem okolju LabView firme National Instruments. Rezultati meritev statičnih karakteristik različnih tipov merjencev, kot so: upor, dioda, tranzistor, zener dioda in tristor, potrjujejo uspešnost predstavljene metode tudi v primerih izbire dokaj malega števila merilnih točk (10-15).

This article presents the current measuring circuit for usage in power meters. The circuit provides a measurement class in a dynamic range over 120 dB with the use of the standard analog-to-digital devices. This large dynamic range is achieved with the appropriate setting of the excitation current of the Hall sensor. Experimental results show that the proposed measuring circuit exceeds the requirements for accuracy and the dynamics that are defined by the IEC687 standard. V članku je predstavljen tokovni merilnik za uporabo v števcih električne energije. Merilnik zagotavlja merilni razred v dinamičnem obsegu več kot 120 dB z uporabo standardnih analogno-digitalnih pretvornikov. Tako veliko dinamiko dosega s primerno nastavitvijo vzbujalnega toka Hallovega sezorja. Eksperimentalni rezultati kažejo, da predlagan merilnik presega po natančnostiin dinamiki, podane v standardu IEC687.