Evaluating the impact of smart technologies on harbor’s logistics via BPMN modeling and simulation

A smart Information and Communication Technology (ICT) enables a synchronized interplay of different key factors, aligning infrastructures, consumers, and governmental policy-making needs. In the harbor’s logistics context, smart ICT has been driving a multi-year wave of growth. Although there is a standalone value in the technological innovation of a task, the impact of a new smart technology is unknown without quantitative analysis methods on the end-to-end process. In this paper, we first present a review of the smart ICT for marine container terminals, and then we propose to evaluate the impact of such smart ICT via business process model and notation (BPMN) modeling and simulation. The proposed approach is discussed in a real-world modeling and simulation analysis, made on a pilot terminal of the Port of Leghorn (Italy).     

Comparison of FEC types with regard to the efficiency of TCP connections over AWGN satellite channels

Optimizing the end-to-end throughput of a TCP connection (goodput) over geostationary satellite links is a challenging research topic. This is because the high delay-bandwidth product, together with a non-negligible random loss of packets, is a condition that considerably differs from the environments TCP was originally designed for. As a result, TCP performance is significantly impaired by the channel bit error rate. The literature is full of suggestions for improving TCP goodput, most based on modifications of the protocol itself. We only investigated the application of different FEC (forward error correction) types for TCP goodput optimization, leaving the end-to-end protocol unaltered. Using a method midway between analysis and simulation to evaluate the goodput of TCP long-lived connections, we first studied the influence of packet loss rate, introduced by errors on the channel, on the TCP goodput. We showed that, in some cases, the packet loss rate does not need to be negligible with respect to that caused by congestion, as it is widely-held opinion. We then applied physical-level FEC techniques, such as convolutional encoding/Viterbi decoding, Reed Solomon, link-level erasure codes and their combinations, over a wide field of signal to noise conditions of the satellite channel. For each FEC type, we found the FEC rate that maximizes the TCP goodput, in each channel condition. We finally compared the results of all FECs used between them, and presented the case of multiple TCP connections sharing the same link as well     

A Traffic Generator for Testing Communication Systems: Presentation,Implementation and Performance

This paper presents a multi-application traffic generator (MTG), aimed at the generation of packets over a LAN. The generated traffic simulates the one produced by a number of both isochronous and anisochronous applications, thus allowing the measurement of a number of parameters relevant to the communication network. From a test point of view, data generated by the MTG system is equivalent to data generated by real applications spread over a LAN. The MTG system is presented, its implementation is described, some figures relevant to the MTG performance are shown, and the statistical analysis which can be performed on the recorded data is briefly introduced. The user manual of the MTG system is referenced in (Celandroni, Ferro, and Potorti 1995).     

Quality estimation of PSK modulated signals

The use of the Ka band (30/20 GHz) for satellite communication systems raises the problem of dealing with rain attenuation. A very important problem in fade countermeasure systems is the need to detect signal quality quickly and accurately. In fact, the countermeasure has to be initiated before the signal degradation effect an the bit error rate is detected by the user. This article presents an overview of different methods to evaluate signal quality, which are based on the availability of soft quantized levels of PSK demodulated signals at the receiver. It is shown that this class of methods has a good theoretical performance. Also, an innovative procedure is presented which adapts one of the methods to some existing hardware, and tunes up a set of parameters in order to compensate for the fact that the hardware is to same extent impaired     

On elastic traffic via contention resolution diversity slotted aloha satellite access

This paper presents a performance study relative to the coupling of the Transmission Control Protocol (TCP) with the Contention Resolution Diversity slotted aloha (CRDSA) protocol, in the case of greedy TCP connections (also called elephants) on Digital Video Broadcasting‐Return Channel via a geostationary satellite. CRDSA, which takes advantage of interference cancellation algorithms for collision/contention resolution, has already exhibited interesting performance when the power levels of all received bursts are perfectly balanced. In this paper, we extend the study to a more realistic case, where a certain spreading of the bursts' power levels is taken into account. The consequent capture effect even facilitates the collision resolution mechanism and yields an improvement in the overall TCP performance with respect to the balanced case. Furthermore, in certain conditions, the adoption of packet level forward error correction allows achieving even higher peaks of throughput than the expected ones. Copyright © 2014 John Wiley & Sons, Ltd.     

Suitability of DAMA and Contention-Based Satellite Access Schemes for TCP Traffic in Mobile DVB-RCS

The problem of optimizing access and bandwidth sharing among transmission control protocol (TCP) connections in the mobile digital video broadcasting return channel via satellite (DVB-RCS) is tackled in this paper. After sketching the general system architecture, we explicitly deal with the dynamic assignment of bandwidth to TCP connections on the return link, which is accomplished by a network control center (NCC) placed onboard the satellite. Mobile users access the satellite in multifrequency time-division multiple access (MF-TDMA), whereas they receive data from the NCC in time-division multiplexing (TDM). Two different techniques, based on deterministic and random access, are compared in terms of bandwidth usage and average completion time per connection, when the mobile user acts as both server and client. In the server case, to increase the TCP throughput, both packet-level forward error correction (FEC) on data sent by mobile users and a duplicated and delayed acknowledgment technique for TCP acknowledgment traffic from the NCC to the mobile users are applied. An analysis of the packet losses and a simulation campaign of file transfers by employing a realistic channel model has been carried out. The results of the analysis show the convenience of adopting a technique, in addition to the optimal data redundancy in different cases, such as the server or client role of users, their willingness to pay, the file size, and the environment type.     

A bandwidth assignment algorithm on a satellite channel for VBR traffic

Variable bit rate (VBR) video is currently by far the most interesting and challenging real-time application. A VBR encoder attempts to keep the quality of video output constant and at the same time reduces bandwidth requirements, since only a minimum amount of information has to be transferred. On the other hand, as VBR video traffic is both highly variable and delay-sensitive, high-speed networks (e.g. ATM) are generally implemented by assigning peak rate bandwidths to VBR video applications. This approach may, however, be inefficient in a satellite network based on a TDMA scheme. To overcome this problem, we have designed a demand assignment satellite bandwidth allocation algorithm in TDMA, named V2L-DA (VBR 2-Level Demand Assignment), which manages the VBR video traffic according to a dynamic bandwidth allocation algorithm. In this paper we discuss how to tune the proposed algorithm in order to optimize network utilization when MPEG-1 VBR video traffic is being transmitted. Our results indicate that most of the time only 40% of the peak rate bandwidth is needed to satisfy the VBR source, so the remaining 60% of the peak rate bandwidth can be used to transmit the datagram traffic queued in the network stations. © 1997 John Wiley & Sons, Ltd.     

Detection of errors recovered by decoders for signal qualityestimation on rain-faded AWGN satellite channels

We describe a method for estimating satellite link quality for use with rain fade countermeasures. The method applies to convolutionally encoded bit streams. It is based on the measurement of the uncoded data bit-error rate (BER) which is estimated by monitoring the errors recovered by a Viterbi decoder. Using a previously developed attenuation model, the measurement time intervals are optimized for a simple application, and the performance of the estimator is shown     

Effect of dairy product environment on the growth of Bacillus cereus

pH is one of the most important parameters to manage bacterial replication in foodstuffs. In this study, the ability of 2 Bacillus cereus strains, 1 clinical human isolate (GPe2) and 1 isolate from a dairy product (D43), were investigated for in vitro growth at different pH values (from 3.5 to 7.5) at 2 temperatures (15 and 37°C), showing their ability to grow from 5.5 to 7.5 and from 5.0 to 7.5, respectively. The ability of spores of these 2 microorganisms to germinate in different typologies of dairy products (unflavored yogurt, Taleggio cheese, mascarpone cheese, and raw and pasteurized milk) was also investigated by inoculating the spores and maintaining the products at 15°C. No growth was observed in yogurt, likely due to the combined effect of low pH (<5) and the presence of natural microflora. An inhibitory action of the natural microflora on the growth of B. cereus was also hypothesized for Taleggio cheese and raw milk, as these substrates were characterized by a high natural lactic acid bacteria population and permissive pH values (5.8/6.8 in Taleggio cheese, >7 in raw milk). In pasteurized milk and mascarpone cheese, where pH was not restrictive for B. cereus growth and where no significant natural microflora was present, growth occurred rapidly up to loads close to 7 log cfu/g.