Computing blocking probabilities in multiclass wavelength-routingnetworks with multicast calls

We present an approximate analytical method to compute efficiently the call-blocking probabilities in wavelength-routing networks with multiple classes of both unicast and multicast calls. Our approach involves the following steps. We start with an approximate solution to a linear single-class unicast network which we developed earlier. Next, all classes of calls on a particular route are aggregated to give an equivalent single-class model. We then extend the path decomposition algorithms that we have developed for single-class networks to handle mesh networks with multiple classes of calls. We show how to use these path decomposition algorithms to decompose large networks with multicast paths into smaller subsystems with only linear paths, which, in turn, are solved by the product-form approximation algorithm. We also consider a state-dependent Poisson arrival process for multicast calls which is more accurate in capturing the behavior of these calls     

Hierarchical Queue Networks with Partially Shared Servicing

The queue network studied consists of n infinite queues in parallel served by independent servers and by other servers all linked to form a hierarchical structure. The total service a unit receives depends partially on other units in service. We call this type of servicing partially shared servicing. All interarrival times as well as service times are assumed exponentially distributed. The characteristic of interest is the traffic intensity of the infinite queues. Some simple formulae are obtained. An application to modelling a disc I/O system is described. The model turns out to be useful and accurate with wide applicability.     

New off-line aircraft instrumentation for non-methane hydrocarbon measurements

New off-line instrumentation was developed to implement measurements of non-methane hydrocarbons (NMHC) on (French) research aircraft. NMHC are collected on multisorbent tubes by AMOVOC (Airborne Measurements Of Volatile Organic Compounds), a new automatic sampler. AMOVOC is a versatile and portable sampler targeting a wide range of NMHC at high frequency (sampling time of 10 min). Multisorbent tubes are analyzed on the ground by short-path thermal desorption coupled with gas chromatography and mass spectrometry. The development and optimization of both NMHC sampling and analysis are reported here. On the one hand, the paper points out technical choices that were made according to aircraft constraints and avoiding sample loss or contamination. On the other hand, it describes analytical optimization, tube storage stability, and moisture removal. The method shows high selectivity, sensitivity (limit of detection less than 10 ppt) and precision (less than 24%). Finally, NMHC data collected on French aircraft during the African Monsoon Multidisciplinary Analysis campaign are reported for the first time. The results highlight instrumentation validity and protocol efficiency for NMHC measurements in the lower and upper troposphere.     

Techniques for optical packet switching and optical burst switching

Wavelength-division multiplexing appears to be the solution of choice for providing a faster networking infrastructure that can meet the explosive growth of the Internet. Several different technologies have been developed so far for the transfer of data over WDM. We survey two new technologies which are still in the experimental stage-optical packet switching and optical burst switching-and comment on their suitability for transporting IP traffic     

Surface passivation of GaAs nanowires by the atomic layer deposition of AlN

It is shown that the atomic layer deposition of thin AlN layers can be used to passivate the surface states of GaAs nanowires synthesized by molecular-beam epitaxy. Studies of the optical properties of samples by low-temperature photoluminescence measurements shows that the photoluminescence-signal intensity can be increased by a factor of up to five by passivating the nanowires with a 25-Å-thick AlN layer.     

Jitter analysis of an IPP tagged traffic stream in an {IPP,M}/M/1 queue

We study a single server queue with two different arriving streams, a tagged arrival process and a background arrival process. The tagged traffic is assumed to be an interrupted Poisson process (IPP) and the background traffic is Poisson. The service time is exponentially distributed, and customers are served in a FIFO manner. We obtain numerically the probability density function of the inter-departure time of the IPP tagged arrival process, from which we calculate its jitter, defined as a percentile of the inter-departure time. Numerical results of the 95th percentile and the squared coefficient of variation of the tagged inter-departure time are given as a function of the arrival rate of the background traffic.     

An introduction to optical burst switching

Optical burst switching is a promising solution for all-optical WDM networks. It combines the benefits of optical packet switching and wavelength routing while taking into account the limitations of the current all-optical technology. In OBS, the user data is collected at the edge of the network, sorted based on a destination address, and grouped into variable sized bursts. Prior to transmitting a burst, a control packet is created and immediately sent toward the destination in order to set up a bufferless optical path for its corresponding burst. After an offset delay time, the data burst itself is transmitted without waiting for a positive acknowledgment from the destination node. The OBS framework has been widely studied in the past few years because it achieves high traffic throughput and high resource utilization. However, despite the OBS trademarks such as dynamic connection setup or strong separation between data and control, there are many differences in the published OBS architectures. In this article we summarize in a systematic way the main OBS design parameters and the solutions that have been proposed in the open literature.     

Resource allocation in the new fixed and mobile Internet generation

In this paper we study the scalability issue in the design of a centralized policy server controlling resources in the future IP‐based telecom network generation. The policy servers are in charge of controlling and managing QoS, security and mobility in a centralized way in future IP‐based telecom networks. Our study demonstrates that the policy servers can be designed in such a manner that they scale with increase in network capacity. Copyright © 2003 John Wiley &Sons, Ltd.     

Nested sliding window protocols with packet fragmentation

A single-hop OSI structured network with multiple layers of sliding window flow control and packet fragmentation between layers is analyzed. An approximation algorithm is presented to hierarchically reduce the network to a single queue whose performance characteristics represent the original network. Network transmission characteristics are restricted to Erlang distributions. Validation against exact and simulation results showed that the approximation algorithm has a satisfactory error level     

A path decomposition approach for computing blocking probabilitiesin wavelength-routing networks

We study a class of circuit-switched wavelength-routing networks with fixed or alternate routing and with random wavelength allocation. We present an iterative path decomposition algorithm to evaluate accurately and efficiently the blocking performance of such networks with and without wavelength converters. Our iterative algorithm analyzes the original network by decomposing it into single-path subsystems. These subsystems are analyzed in isolation, and the individual results are appropriately combined to obtain a solution for the overall network. To analyze individual subsystems, we first construct an exact Markov process that captures the behavior of a path in terms of wavelength use. We also obtain an approximate Markov process which has a closed-form solution that can be computed efficiently for short paths. We then develop an iterative algorithm to analyze approximately arbitrarily long paths. The path decomposition approach naturally captures the correlation of both link loads and link blocking events. Our algorithm represents a simple and computationally efficient solution to the difficult problem of computing call-blocking probabilities in wavelength-routing networks. We also demonstrate how our analytical techniques can be applied to gain insight into the problem of converter placement in wavelength-routing networks