Sip Overload Control Testbed: Design, Building and Evaluation

Having facilities such as being in text form, end-to-end connection establishment, and being independence from the type of transmitted data, SIP protocol is a good choice for signaling protocol in order to set up a connection between two users of an IP network. Although utilization of SIP protocol in a wide range of applications has made various vulnerabilities in this protocol, amongst which overload could make serious problems in SIP servers. A SIP is overloaded when it does not have sufficient resources (majorly CPU processing power and memory) to process all messages. In this paper the window-based overload control mechanism which does not require explicit feedback is developed and implemented on Asterisk open source proxy and evaluated. The results of implementation show that this method could practically maintain throughput in case of overload. As we know this is the only overload control method which is implemented on a real platform without using explicit feedback. The results show that the under load server maintains its throughput at the maximum capacity.Comment: 10 pages, 9 figures, 2 table, 37 reference

Estimating Watermarking Capacity in Gray Scale Images Based on Image Complexity

Capacity is one of the most important parameters in image watermarking. Different works have been done on this subject with different assumptions on image and communication channel. However, there is not a global agreement to estimate watermarking capacity. In this paper, we suggest a method to find the capacity of images based on their complexities. We propose a new method to estimate image complexity based on the concept of Region Of Interest (ROI). Our experiments on 2000 images showed that the proposed measure has the best adoption with watermarking capacity in comparison with other complexity measures. In addition, we propose a new method to calculate capacity using proposed image complexity measure. Our proposed capacity estimation method shows better robustness and image quality in comparison with recent works in this field

Egyensúlyi fázisdiagrammok számítása ESTPHAD módszerrel = Calculation of Equilibrium Phase Diagrams by ESTPHAD method

Az egyensúlyi fázisdiagramok igen jelentős része csak grafikusan ismert, vagy - egy csekély hányaduk -komplikált, igen hosszú CPU időt lekötő eljárással számítható ki. Ez a felismerés vezetett az ESTPHAD módszer és szoftver kidolgozásához. A módszer alapja az átalakulási hőmérsékletet leíró -termodinamikai összefüggésekből levezetett- egyenletek, melyekkel kiszámíthatók az átalakulások kezdő és befejező hőmérsékletei. A rendszer hierarhikus, azaz a többalkotós rendszerek egyenletei tartalmazzák az alacsonyabb rendű rendszerek állandóit. Az állandók mért, grafikusan ismert vagy valamely termodinamikai számításból kapott adatokból regresszióval határozhatók meg. A munka során 16 kétalkotós vas, 12 kétalkotós alumínium alapú, számos réz és nemesfém alapú kétalkotós rendszer vonalainak adatait dolgoztuk fel egészben vagy részben. A kétalkotós alumínium alapú ötvözetek adatait felhasználva 4 háromalkotós egyensúlyi fázisdiagram alumínium sarkának likvidusz és szolidusz felületeinek az egyenleteit is meghatároztuk. Feldolgoztuk 6 binér, 4 ternér és egy kvaternér oxid rendszert is. A rendszer egyszerű felhasználása érdekében egy szabadon felhasználható szoftvert dolgoztunk ki. A szoftver alkalmas az adatbázisban való keresésre, valamint lehetőség nyílik olyan szoftver részek letöltésére, amelyeket a szimulációs programba építve bárki ki tudja számítani az egyensúlyi fázisdiagramok adatait. A szoftver és az adatbázis a www.matsci.uni-miskolc.hu/estphad honlapról szabadon letölthető. | The majority of phase equilibria are known only in graphically presented phase diagrams. Alternatively, it can be computed using a so-called Calphad method. The latter, however, requires long CPU times for the numerical solution. This situation lead us to the idea to develop a new method and a computer code called Estphad. The method is based on thermodynamically derived equations. The Estphad system is hierarchically built. The coefficients of Estphad can be obtained by regression analysis, using measured data, graphical phase diagram, or data obtained by a Calphad computer code. Equilibrium lines of 16 binary iron-, 12 binary aluminum-based, and a number of binary copper-based and precocious metal-based systems have been evaluated. Using the data obtained for the binary aluminum-based alloys, equations, describing the solidus and liquidus surfaces in the Al-corners of four ternary aluminum based systems have been obtained, as well. Additionally six binary, four ternary and one quaternary oxide phase diagrams have been calculated. To ensure a simple and widespread use of our new Estphad system, an open computer code has been developed. The code let anyone to search in the existing database. Also, one can download specific fragments of the code, which can be useful as sub-routines in larger simulation programs to calculate phase equilibrium data. The code and the existing database can be downloaded free of charge from the website www.matsci.uni-miskolc.hu/estphad

Electrically tuned microwave devices using liquid crystal technology

An overview of liquid crystal technology for microwave and millimeter-wave frequencies is presented. The potential of liquid crystals as reconfigurable materials arises from their ability for continuous tuning with low power consumption, transparency, and possible integration with printed and flexible circuit technologies. This paper describes physical theory and fundamental electrical properties arising from the anisotropy of liquid crystals and overviews selected realized liquid crystal devices, throughout four main categories: resonators and filters, phase shifters and delay lines, antennas, and, finally, frequency-selective surfaces and metamaterials.Pouria Yaghmaee, Onur Hamza Karabey, Bevan Bates, Christophe Fumeaux and Rolf Jakob

High Load Control Mechanism for SIP Servers

To start voice, image, instant messaging, and generally multimedia communication, session communication must begin between two participants. SIP (session initiation protocol) that is an application layer control induces management and terminates this kind of sessions. As far as the independence of SIP from transport layer protocols is concerned, SIP messages can be transferred on a variety of transport layer protocols including TCP or UDP. Mechanism of Retransmission that is embedded in SIP could compensate for the missing packet loss, in case of need. This mechanism is applied when SIP messages are transmitted on an unreliable transmission layer protocol like UDP. Also, while facing SIP proxy with overload, it could cause excessive filling of proxy queue, postpone increase of other contacts, and add to the amount of the proxy overload. In the present work, while using UDP as transport layer protocol, invite retransmission timer (T1) was appropriately regulated and SIP functionality was improved. Therefore, by proposing an adaptive timer of invite message retransmission, attempts were made to improve the time of session initiation and consequently improve the performance. Performance of the proposed SIP was implemented and evaluated by SIPP software in a real network environment and its accuracy and performance were demonstrated

High Load Diminution by Regulating Timers in SIP Servers

To start voice, image, instant messaging, and generally multimedia communication, session communication must begin between two participants. SIP (session initiation protocol) that is an application layer control induces management and terminates this kind of sessions. As far as the independence of SIP from transport layer protocols is concerned, SIP messages can be transferred on a variety of transport layer protocols including TCP or UDP. Mechanism of Retransmission that is embedded in SIP could compensate for the missing packet loss, in case of need. This mechanism is applied when SIP messages are transmitted on an unreliable transmission layer protocol like UDP. Also, while facing SIP proxy with overload, it could cause excessive filling of proxy queue, postpone increase of other contacts, and add to the amount of the proxy overload. In the present work, while using UDP as transport layer protocol, invite retransmission timer (T1) was appropriately regulated and SIP functionality was improved. Therefore, by proposing an adaptive timer of invite message retransmission, attempts were made to improve the time of session initiation and consequently improve the performance. Performance of the proposed SIP was implemented and evaluated by SIPP software in a real network environment and its accuracy and performance were demonstrated

Does the H-1B Visa Program Impact Quality of Healthcare?

Recently, the H-1B visa program has been a target of reform under the Trump administration. This study explores whether the employment of H-1B physicians in U.S. hospitals has any effect on the quality of healthcare provided. As indicators of quality, I use patient survey scores as well as mortality and readmission rates. This new econometric evidence suggests that patient perception of quality is not influenced by prejudice toward nonimmigrant physicians, but provides inconclusive results for the rate-based measures of healthcare quality