A Bloom Filter is an efficient randomized data structure for membership queries on a set with a certain known false positive probability. Bloom Filters (BFs) are very attractive for their limited memory requirements and their easy construction which make them a popular choice for many tasks in network devices. However, in a number of network applications, more than simple probabilistic membership queries is required, and BFs can be adopted as a coarse filtering stage, leaving the ultimate filtering and classification process to other techniques, such as hash tables or tree-like structures. In this paper we propose a scheme to extend BFs with "indexing" features so that when an element x is queried, an univocal index of that element is returned, which in turn can be used as an address for a table, just as a perfect hashing scheme. This extension, called indexed Bloom Filter (iBF), comes at the cost of a small increment of false positive probability and simply fits in existing BF-based applications.

The high level of performance achieved by todays traditional PCs makes x86 personal computers effective and inexpensive platforms for the development of high performance network devices. In particular, such devices can replace, especially in the access portion of the network, traditional devices for operations like management, monitoring and accounting. This new possibility pushes the research towards the development of new algorithms and functionalities on top of the x86 architecture. In this framework, the purpose of this work is to design a new high-speed longest prefix classification algorithm for packet accounting to be integrated on top of Linux based PCs for traffic characterization and accounting on high speed (> 1Gbps) links, regardless of the detail level of the rule set.

This paper presents a simulative analysis of a modification to the TCP congestion control mechanism called ESSE (early slow start exit), designed to improve the TCP startup phase by setting the slow start threshold according to a pipesize estimation based on the observation of few ACK arrival times. We evaluate the performance of ESSE by using various methods to estimate the pipesize as the ratio between the round trip time and the spacing between ACK. This algorithm is easy to implement and preserves the compatibility with the standard protocol since it requires changes to the sender side only. Simulative experiments show that ESSE allows us to speed-up TCP connections and drastically reduce the packet drop rate under several working conditions and load levels. Better performance of TCP can be observed for any of the considered estimators, which indicates that the algorithm is robust against estimation errors. Further, the characteristics of fairness and friendliness (towards Newreno) of the algorithm are investigated. According to our simulations, ESSE-modified protocols guarantee fair utilization of bandwidth among homogeneous and heterogeneous (Newreno) connections sharing a common link.

The paper presents a comparison of several traffic models in order to investigate their adequacy to approximate the behaviour of actual traffic in a single server queue under realistic working conditions. Hence, considering queueing systems with finite buffers, models parsimoniously fitting the long range dependence (LRD) property are compared to intrinsically short range dependent models and to flexible ones, capturing both LRD and short range dependence (SRD). The paper highlights an optimistic queueing behaviour evaluated by means of models capturing only LRD property, when realistic buffer sizes are considered and a strong SRD correlation component is present. The simulation results point out that the circulant modulated Poisson processes (CMPP) and fractional autoregressive integrated moving average (p,d,0) (f-ARIMA(p,d,0)) are suitable models to estimate the performance of the queueing system under heavy load conditions. On the contrary, when the system works under low-medium load conditions, the relevance of the marginal distribution to queueing performance and the inaccuracy of the CMPP model on fitting this statistic in the case of actual traffic data lead to a reduction of the accuracy of this model on system performance evaluation.

Preventive actions have to be used to avoid congestion in ATM networks. These actions are represented by call admission control (CAC) and usage parameter control functions (UPC). Two UPC algorithms are compared and an enhancement of the leaky bucket mechanism is presented. The comparison is based on the results of several trace driven simulations. The simulations, realised on a CAMAD tool, are driven by MPEG1 video traces as input traffic. The effectiveness of the proposed algorithm has been evaluated in terms of response time and transparency. These performance indexes have been obtained considering the number of non-conforming cells and the mean value of the conforming cells path.

In this paper we analyze the synchronization properties of a digital loop conceived for PSK carrier recovery. The effects of a frequency step and additive Gaussian noise are evaluated by means of the Markov chain technique.

A first-order nonuniform multilevel quantized DPLL is analyzed in the presence of a phase- and frequency-step signal plus Gaussian noise. The system is modeled as a homogeneous finite Markov chain. In this way, closed-form expressions are obtained for the steady-state probabilities, the mean and rms values of the phase error, and the mean number of samplings to slip a cycle or to reach acquisition. Numerical results are also presented.

A non-uniform sampling digital phase locked loop (DPLL), with a hard limiter as quantizer, is analyzed by a graphical method in the case of phase and frequency step inputs and no noise. The cycle slipping and the limit cycles phenomena are investigated. An upper-bound to the model gain and, consequently, to the pull-in range is obtained. Also a closed-form expression of acquisition time is derived. Moreover, using a random-walk model, the stationary phase error variance, the mean acquisition time and the mean first slip time have been evaluated. Some two channel configurations are proposed, which allow us to obtain a faster acquisition. Finally the problems relevant to the practical implementation of the loop are analyzed.

By using a quasi-stationary approximation a closed form expression is derived for the acquisition time of a third-order swept tracking system, with an arbitrary phase-detector characteristic and with nonideal as well as with ideal integrating filter, optimized for tracking or demodulation in the absence of noise with large initial detuning (relative to the noise bandwidth). For sinusoidal phase detector with ideal or nonideal filters, exact solutions confirm theoretical predictions.