A. La Corte

Modeling superposition of ON-OFF correlated traffic sources in multimedia applications

In this paper a multimedia source is modeled as an arrival process defined as the superposition of heterogeneous correlated arrival processes, each of which models one monomedia source. To this purpose each monomedia source is modeled as an ON-OFF process where the transition rates are functions of the states of the other monomedia sources. Auto- and cross-correlation functions are derived for each monomedia source. The analytical model is used to develop results for single media performance in a multimedia multiplexer structure.

An analytical paradigm to calculate multiplexer performance in an ATM multimedia environment

In this paper a finite-buffer discrete-time approach is presented in order to analyze the performance of a multiplexer loaded by N multimedia sources. For this purpose the emission process of each multimedia source is defined as the superposition of heterogeneous correlated emission processes, each of which models one monomedia source as a Switched Batch Bernoulli Process (SBBP). In order to model the intermedia relationships, the Markov chain underlying each SBBP consists of a 2-state process, where the transition probabilities are functions of the states of the other monomedia sources. Correlation functions are derived for each monomedia source as well as for the multimedia source as a whole. The proposed analytical model is used to calculate the loss probability and the delay jitter pdf for each media in an ATM multimedia multiplexer structure. The effectiveness of the proposed paradigm is shown by means of various examples in a case study.

Modeling activity in VBR video sources

Abstract Variable bit-rate (VBR) video sources are significantly characterized by the statistics of ‘scene changes’, which determine the activity exhibited by the pictures. In a source coded with an interframe technique, in fact, this characteristic is related to the length of the emission periods having a very high bit-rate. It therefore represents a fundamental feature in evaluating performance of a network supporting video traffic. In this paper an emission process that is able to fit different activity measurements for VBR video sources characterized by a predefined bit-rate probability density function is introduced. Such a process is based on a suitable linear combination of continuous state autoregressive Markov processes. It is analyzed with respect to its capability to match the actual values of some temporal parameters which have been introduced to characterize the source. Its modeling power is compared with that of a single autoregressive Markov process. In particular is demonstrated that the process introduced here can model faster motion within a scene than a single autoregressive Markov process. Finally a case study is introduced to point out the flexibility of the proposed process.

Nonstationary magnetization dynamics driven by spin transfer torque

This paper shows that the presence of two dynamical regimes, characterized by different precessional axes, is the origin of the nonmonotonic behavior of the output integrated power for large-amplitude magnetization precession driven by spin-polarized current in nanoscale exchange-biased spin valves. In particular, an abrupt loss in the integrated output power exists at the transition current between those two regimes. After the introduction of a time-frequency analysis of magnetization dynamics based on the wavelet transform, we performed a numerical experiment by means of micromagnetic simulations. Our results predicted that, together with a modulation of the frequency of the main excited mode of the magnetization precession, at high nonlinear dynamical regime the instantaneous output power of the spin-torque oscillator can disappear and then reappear at nanosecond scale.

Statistical voice/high-speed data multiplexing on a 64 kbit/s channel

The authors describe a method for the immediate recognition of signal transitions in voice/data multiplexing which allows effective transmission of high-speed data during silences in a telephone conversation. In particular the authors define the procedures through which synchronization can be recovered in the occurrence of false or undetected transitions between the two signal types. A statistical multiplexer based on this method is presented which can be used at source by a single user of a 64 kb/s pulse-code-modulation (PCM) telephone channel. The multiplexer efficiency has been enhanced by using a speech detector whose threshold values are dynamically adapted to the background noise and to amount of data queued for transmission. The design of such a multiplexer is assessed by simulations whose major results are presented.<<ETX>>

A new algorithm for fast synchronization in a burst mode PSK demodulator

In burst mode communication systems rapid carrier and clock synchronization is essential. The authors propose a dedicated algorithm for initial estimation of synchronization parameters in a PSK demodulator which works in a single channel per carrier (SCPC) mode. The algorithm is based on a very short special carrier preamble modulated by a known pattern, which allows the reference parameters to be estimated simultaneously and directly. The algorithm was implemented, together with the whole PSK demodulator, on a Texas Instruments TMS320C31 digital signal processor (DSP). Since the demodulator is entirely digital and thanks to its implementation by means of low power VLSI technology it is suitable for portable communication applications.

Extending the MASIF location service in the MAP agent system

A previous development in the field of telecommunication networks has enabled the evolution of distributed systems, and has favoured the development of a new generation of applications based on the use of mobile agents. In fact, during the last few years, several agent platforms have been created; however the architectures and implementation of such platforms are very different, and this makes their interaction difficult. In order to favour the interaction among differently implemented platforms, the Object Management Group (OMG) has proposed the Mobile Agent System Interoperability Facility (MASIF) standard, which includes some definitions and interfaces which all platforms have to comply with. We present the MAP platform for developing and managing mobile agents; it complies with MASIF in order to communicate and interact with similar platforms provided that they comply with the mentioned standard. Besides, we present a mechanism, which has been implemented in the MAP, which extends MASIFs functionalities so to enable the interaction among agents and agent systems operating in different regions.

A feedback approach for jitter and skew enforcement in multimedia retrieval services

End-to-end delay jitter has a great impact on the continuity of playback of information. A system supporting multimedia services has to be equipped with functions which will guarantee intra/intermedia synchronization requirements by limiting variations in the delay jitter. In this paper an end-to-end mechanism to meet the intra/intermedia synchronization requirements of a distributed multimedia retrieval service is introduced. The mechanism is based on a prediction of the network delay jitter suffered by each information unit at the destination site and retrieval time modification at the source site in such a way to reshape the delay jitter and skew probability density functions.

A DSP implemented speech/voiceband data discriminator

A very powerful speech/voiceband-data discriminator on a 64 kb/s PCM (pulse code modulation) channel, implemented on a single-chip digital signal processor, is presented. Its performance has been evaluated by external simulation (modem for data, recorded tape for speech), giving very good results in terms of response time and false detection probability. The increased clipping of incoming speech channels in DSI (digital speech interpolation) and the limitations of the CCIT G.721 ADPCM (adaptive differential PCM) encoding algorithm with respect to data transmission are pointed out. The total elaboration time to perform discrimination on a single channel is less than 62 mu s when a TMS32020 is used. A two-channel speech/voiceband-data discriminator could be implemented on a faster and more powerful digital signal processor.<<ETX>>

Jitter analysis in an ATM multimedia multiplexer

The delay jitter affecting a monomedia traffic stream, when N multimedia streams are mixed in an ATM multiplexer, is evaluated. To this purpose a multimedia source is modeled as an arrival process defined as the superposition of heterogeneous correlated arrival processes, each of which models one monomedia source by means of an on-off process whose transition rates are functions of the states of the other monomedia sources.