Abstract-While Software Defined Networking (SDN) has received a considerable amount of attention, improving the scalability of an SDN controller has always been a major concern. One of the main reasons why the controller suffers from this scalability problem is that it is fairly often overwhelmed by a large number of flow setup requests from the SDN switches to the controller. These requests cause decrease in the number of switches that the controller can deal with. Since these requests are usually generated when flows arrive at the switch and their corresponding entries do not exist in the flow table due to eviction, minimizing the number of evictions also reduces the number of requests to the controller. This paper addresses the scalability problem and proposes the algorithm improving the scalability of the SDN controller by dynamically controlling the timeout value of each flow without modifying the switches. In the proposed approach, the controller collects various traffic parameters from the switches and predicts the inter-arrival times of packets in a flow. Based on the information, it dynamically adjusts the timeout value of each flow to reserve spaces in the flow table for newly arrived flows in advance. As a result, this avoids the evictions and reduces the number of flow setup requests to the controller. The benchmarking results show that the proposed algorithm reduces the number of packets to the controller by 9.9 %.

-This paper proposed an Spread Spectrum Time Domain Reflectometry (SSTDR) using time-frequency correlation analysis in order to have more accurate fault determination and location detection than classical SSTDR despite increased signal attenuation due to the long distance to cable fault location. The proposed method was validated through comparison with classical SSTDR methods in open-and short-circuit fault detection experiments of low-voltage power cables. The experimental results showed that the proposed method can detect correlation coefficients at fault locations accurately despite reflected signal attenuation so that cable faults can be detected more accurately and clearly in comparison to existing methods.

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STDR (sequence time domain reflectometry) to detect a cable fault using a pseudo noise sequence as a reference signal, and time correlation analysis between the reference signal and reflection signal is robust to noisy environments and can detect intermittent faults including open faults and short circuits. On the other hand, if the distance of the fault location is far away or the fault type is a soft fault, attenuation of the reflected signal becomes larger; hence the correlation coefficient in the STDR becomes smaller, which makes fault detection difficult and the measurement error larger. In addition, automation of the fault location by detection of phase and peak value becomes difficult. Therefore, to improve the cable fault detection of a conventional STDR, this paper proposes the algorithm in that the peak value of the correlation coefficient of the reference signal is detected, and a peak value of the correlation coefficient of the reflected signal is then detected after removing the reference signal. The performance of the proposed method was validated experimentally in low-voltage power cables. The performance evaluation showed that the proposed method can identify whether a fault occurred more accurately and can track the fault locations better than conventional STDR despite the signal attenuation. In addition, there was no error of an automatic fault type and its location by the detection of the phase and peak value through the elimination of the reference signal and normalization of the correlation coefficient.

-This paper presents few case studies of state diagnosis of XLPE cables using very low frequency techniques. The power cables of 22.9kV which have installation fault were assessed using VLF technique in addition to other techniques like insulation resistance and DC voltage withstand test. From the experimental results, The dielectric loss(tanδ) values of degradation of the cable(joint, knife, needle) at U 0 were 5.839, 5.526 and 6.251, respectively and all values were "further study advised". VLF PD measurement was also found defective portion. These method was effective in defect to fault in the degradation of the cable. However, the breakdown did not occur in the degradation of the cable because of properties of XLPE insulation. Few case studies of using VLF tanδ diagnosis for fault are measured and analyzed. The tanδ values at U 0 were "further study advised" or "action required".