Jorge Mata

Bidimensional fluid model for VBR MPEG video traffic

The broadband bandwidth of ATM networks allows to develop new video services. To reduce the resource allocation in these networks, the video services employ compression techniques. The most common used technique is the MPEG algorithm. In order to maintain the image quality the MPEG coders generate a variable bit rate. Usually, a smoothing system is inserted between the video coder and the user network interface. The purpose of this system is to improve the performance of ATM networks. In this way, the traffic delivered to the network maximize the multiplexing gain.

Performance of dynamic resources allocation with QoS guarantees for MPEG VBR video traffic transmission over ATM networks

Most of the new and interesting services that can be implemented over the B-ISDN networks include the transmission of variable bit rate (VBR) video traffic. Generally, the nature of this kind of services implies the need of a high quality of service (QoS). Unfortunately, to provide this high QoS to the VBR video traffic with a high efficiency in bandwidth utilization is not a trivial problem. This is due to the bursty nature of the VBR video traffic on different time scales. This traffic behavior is named self-similarity. In order to improve channel utilization, some services with bandwidth renegotiation have been proposed. In this work, a new mechanism to accomplish bandwidth renegotiation over ATM networks for VBR video traffic is presented. The mechanism is based on a previous characterization of the MPEG VBR video traffic at the group of pictures (GoP) level by means of a bidimensional Markov modulated fluid process (MMFP). A new element, with supervision and control functions, is proposed and validated. Moreover, the achieved benefits in terms of the bandwidth gain that can be expected with the renegotiation system are analytically computed using the fluid flow approximation. Finally, the applicability of the supervisor and controller elements and its parameters are studied using four long MPEG VBR sequences.

Prediction techniques for VBR MPEG traffic shaping

The use of smoothing techniques to remove the periodic fluctuations of the bit rate generated by the codification modes of the MPEG algorithm is very suitable in video transmission. In this way, the multiplexing gain is maximized and the resource allocation is reduced in ATM networks. The traffic smoothing can be achieved storing the cells in a buffer. This buffer is allocated between the coder and the user-interface. To reduce the delay introduced in the storage process a new technique to forecast the VBR MPEG traffic is presented. This technique is based on the characterization of bits per frame generated by the MPEG coder as an ARIMA process. In this study the invariance of the ARIMA coefficients is verified for all coded sequences. In addition, these coefficients are invariant also in front of the changes of the selected image quality in the coder. This characterization allows one to propose a new traffic shaper scheme when forecast techniques are applied.

Evaluation of Cryptographic Capabilities for the Android Platform

Future networks will be formed by millions of devices, many of them mobile, sharing information and running applications. Android is currently the most widely used operating system in smartphones, and it is becoming more and more popular in other devices. Providing security to these mobile devices and applications is a must for the proper deployment of future networks. For this reason, this paper studies the cryptographic structure and built-in tools in Android, and shows that the operating system has been specially designed for plugging-in external cryptographic modules. We conclude that the best option for providing cryptographic capabilities is using these external modules. We show the existent options and compare some features, like licensing, source code availability and price. We define some requirements, evaluate each module, and provide guidelines for developers who want to use properly security primitives.

Predictive shaping for VBR MPEG video traffic transmission over ATM networks

The use of smoothing techniques to remove the periodic fluctuations of the bit rate generated by the codification modes of the MPEG algorithm is very suitable in video transmission. In this way, the multiplexing gain is maximized and the resource allocation is reduced in ATM Networks. The traffic smoothing can be achieved storing the cells in a buffer. This buffer is allocated between the coder and the user-interface. To reduce the delay introduced in the storage process a new technique to forecast the VBR MPEG traffic is presented. This technique is based on the characterization of bits per frame generated by the MPEG coder as an ARIMA process. In this study the invariance of the ARIMA coefficients is verified for all coded sequences used. In addition, these coefficients are invariant also in front of the changes of the selected image quality in the coder. This characterization allows to propose a new traffic shaper scheme when forecast techniques are applied. Moreover, numerical results allows to compare the smoothing effects introduced, as well as the delays for the classic shaper and the predictive shaper.

Source Traffic Descriptor for VBR MPEG in ATM Networks

Broadband Networks based on the Asynchronous Transfer Mode (ATM) will support, among others, traffic coming from variable bit rate video (VBR) codecs1, which are capable of maintaining a constant picture quality of the decoded image. The characterization of such VBR video sources becomes important in the analysis and design of Broadband Integrated Services Digital Networks (B-ISDN). The network architecture and its characteristics, such as cell-loss probabilities, transmission delay, high-speed statistical multiplexing gain, buffering, etc., are strongly related to the statistical properties of the sources and the coding schemes involved.

Two-level renegotiated constant bit rate algorithm (2RCBR) for scalable MPEG2 video over QoS networks

MPEG family codecs generate variable-bit-rate (VBR) compressed video with significant multiple-time-scale bit rate variability. Smoothing techniques remove the periodic fluctuations generated by the codification modes. However, global efficiency concerning network resource allocation remains low due to scene-time-scale variability. RCBR techniques provide suitable means to achieving higher efficiency. Among all RCBR techniques described in literature, 2RCBR mechanism seems to be especially suitable for video-on demand. The method takes advantage of the knowledge of the stored video to calculate the renegotiation intervals and of the client buffer memory to perform work-ahead buffering techniques. 2RCBR achieves 100% bandwidth global efficiency with only two renegotiation levels. The algorithm is based on the study of the second derivative of the cumulative video sequence to find out sharp-sloped inflection points that point out changes in the scene complexity. Due to its nature, 2RCBR becomes very adequate to deliver MPEG2 scalable sequences into the network cause it can assure a constant bit rate to the base MPEG2 layer and use the higher rate intervals to deliver the enhanced MPEG2 layer. However, slight changes in the algorithm parameters must be introduced to attain an optimal behavior. This is verified by means of simulations on MPEG2 video patterns.