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The multi-AP coordination is a key feature of Wi-Fi 7 (EHT) and is a promising approach to improving the utilization of limited radio resources. However, the APs coordination requires the exchange of information among the APs in the coordination set in order to make the optimal sharing decision with regard to specific performance parameters. In this work, we present the control frames defined for this purpose and the transmission procedures defined in EHT for the multi-AP coordination. We implemented the new frames and EHT procedures in ns-3. Furthermore, we designed and implemented a scheduler with the aim to improving the performance of EHT network in non-saturated conditions by sharing the time resources, i.e., C-TDMA. Then, we assessed the performance of the proposed scheduler in ns-3. Multi-AP coordination through C-TDMA allows for reduction of the network latency of one order of magnitude while keeping the network throughput stable.

In "Software Tools for Networking" column

A food consumption survey on 420 children was conducted in four areas in Benin to identify the local vitamin A (VA)-rich foods most frequently eaten and assess their contribution to the coverage of VA requirements of young children. Mangoes, eggs, red palm oil, various leafy vegetable (LV) sauces and palm nut juice sauce appeared to be the main VA-rich foods consumed. The recipes of the most promising sauces were characterised. Sauces with red palm oil/palm nut juice showed high carotenoid contents ranging from 0.9 +/- 0.3 to 4.0 +/- 0.8 mg Retinol Activity Equivalent/100 g dry matter (DM). Lipid contents were also high (from 39.6 to 66.8 g/100 g DM). When consumed, and taking into account the mean quantity eaten per meal, LV sauces containing red palm oil or palm nut juice contributed to the meeting of more than 70% of the recommended VA intake of young children.

WiFi 6 based on the IEEE 802.11ax amendment is intended to improve spectral efficiency and area throughput operations in high density environments. This is achieved (among other methods) by the introduction of Orthogonal Frequency Division Multiple Access (OFDMA) and enhanced multi-user Multiple Input Multiple Output (MU-MIMO) features. In this work, we explore the performance of downlink and uplink OFDMA in 802.11ax via extensive simulation based evaluation (latency, throughput, range) compared to conventional single user (SU) transmissions. Based on our results, we conclude that OFDMA can reduce the median latency from ∼5 ms to less than 1 ms in non-saturation conditions. When used in conjunction with efficient multi-user buffer status report and restricted EDCA mechanisms, OFDMA can increase the saturation throughput by more than 10 percent. Moreover, UL OFDMA also improves aggregate throughput at longer ranges due to the narrower sub-channels (equivalently increased transmit power spectral density); four stations achieve an aggregate throughput 35 percent higher than a station transmitting SU frames and located at a range 1.5 times closer to the access point.

The Software Defined Network (SDN) paradigm represents a major breakthrough in the networking field, due to its unprecedented capabilities in terms of flexibility and programmability. SDNs have been successfully deployed in data centers and small to medium enterprises. However, adopting the SDN paradigm in the context of wide area networks is more challenging, due to a number of factors including the higher probability that node and link failures occur and the unavailability of a dedicated control channel. In this paper, we present a DAG (Directed Acyclic Graph) based forwarding paradigm addressing the challenges that arise when the SDN concept is applied to large scale networks. Specifically, the proposed paradigm aims to limit the number of entries required on the SDN switches, to provide a fast local restoration of single node/link failures without the intervention of the SDN controller and to prevent the possibility of having inconsistent forwarding tables during updates. The proposed paradigm does not require any extension to the OpenFlow protocol and we show how it can be implemented by only using standard features. The DAG-based forwarding paradigm requires to compute a DAG between every pair of ingress-egress switches and to design an index-based hashing scheme to balance the load across the paths in the DAG while avoiding TCP reordering issues. In this paper, we present heuristic algorithms providing a solution to such problems and report the results of a simulation study conducted to assess the performance of the proposed forwarding paradigm.

Researchers from academia, industry and research centers often resort to emulation to overcome the drawbacks associated with network simulation and experimental evaluation. Emulation is broadly classified in environment emulation, usually carried out by running real code in Virtual Machines (VMs) or containers, and network emulation, typically involving network simulators that exchange packets with the real world. In this paper, we focus on network emulation, which is often exploited for rapid prototyping and testing of network protocols and algorithms. We identify the limitations of the approach currently used by various network simulators to provide network emulation and design an alternative solution based on netmap, a framework for high speed packet I/O which is available on multiple operating systems. We argue that the proposed solution to network emulation provides extremely accurate results in terms of packet latency and packet drops and prove our claim by means of an extensive experimental campaign. We also show that by building upon an accurate network emulation mechanism it is possible to validate the implementation of protocols found in network simulators against their implementation in real network stacks. As an example, we present the results of the experiments we conducted to validate the ns-3 implementation of various packet schedulers against their Linux counterpart.

In this paper, we develop a novel throughput- maximizing OFDMA scheduler for the multi-user MAC framework for the IEEE 802.11ax networks. The scheduler works both in the downlink and uplink directions and assigns resource units to stations using a linear programming technique considering load of each client, possible resource unit configurations, modulation-coding scheme of each client, and ageing factor of each client's load. The performance of the proposed scheduler has been evaluated using the NS3 simulator and compared against the legacy MAC layer mechanism of IEEE 802.11 protocol (i.e., DCF/EDCA). Simulation results show that our proposed throughput-maximizing scheduler increases the total throughput in the network as well as decrease the average end-to-end delay regardless of the number of stations connected to the access point by prioritizing the traffic of clients connected via high modulation-coding schemes.

To overcome the lack of spectrum resources, the proposal of extending LTE (Long Term Evolution) to the readily available unlicensed spectrum is receiving much attention. However, gaining capacity in a band where Wi-Fi is widely used and guaranteeing fairness between systems is not an easy to address issue. Analyzing the impact of operating LTE in the unlicensed band on the performance of Wi-Fi and devising solutions to minimize such an impact have been the goals of a considerable amount of work carried out by the research community, standardization bodies and telecom operators. In this paper, we first present a basic overview of Wi-Fi and LTE, which serves the purpose of illustrating why the fair coexistence of the two technologies in the unlicensed band is an issue. Basically, since LTE has been designed to operate in licensed bands, the centralized scheduling performed by LTE eNodeBs saturates all the channel resources, while Wi-Fi stations refrain from transmitting if the channel is sensed busy. Then, we illustrate the main approaches proposed to ensure a fair coexistence between Wi-Fi and LTE in the unlicensed band, namely Listen Before Talk (LBT) and Almost Blank Subframe (ABS), along with some other minor techniques. We describe the main solutions that are currently being developed by standardization bodies and telecom industry: LTE–U, Licensed Assisted Access (LAA) and MuLTEfire. Finally, we present an overview of the work appeared in the literature analyzing the impact of LTE on the performance of Wi-Fi and proposing solutions to mitigate such an impact.

The problem of bufferbloat arises due to the presence of large unmanaged buffers and leads to high queuing delays and significant degradation in the performance of time-sensitive and interactive Internet applications. Recently, a new smart queue management system called Common Applications Kept Enhanced (CAKE) has been introduced in Linux 4.19 to tackle the problem of bufferbloat in home Internet gateways. One of the integral parts of CAKE system is COBALT (CoDel and BLUE Alternate), a queue discipline which is a combination of Controlled Delay (CoDel) and BLUE algorithms. Although CAKE is a part of the Linux kernel, a detailed discussion on the design of COBALT is missing. In this paper, we discuss the design of COBALT and compare its performance with CoDel. Additionally, we propose a simulation model for COBALT in ns-3 and test its correctness by comparing the results obtained from it to those obtained from the Linux model. Our evaluation shows that COBALT offers substantial benefits in terms of curtailing queue delays when unresponsive flows exist.

Bloated buffers in the Internet add significant queuing delays and have a direct impact on the user perceived latency. There has been an active interest in addressing the problem of rising queue delays by designing easy-to-deploy and efficient Active Queue Management (AQM) algorithms for bottleneck devices. The real deployment of AQM algorithms is a complex task because the efficiency of every algorithm depends on appropriate setting of its parameters. Hence, the design of AQM algorithms is usually entrusted on simulation environments where it is relatively straightforward to evaluate the algorithms with different parameter configurations. Unfortunately, several factors that affect the efficiency of AQM algorithms in real deployment do not manifest during simulations, and therefore, lead to inefficient design of the AQM algorithm. In this paper, we revisit the design considerations of Proportional Integral controller Enhanced (PIE), an algorithm widely considered for network deployment, and extensively evaluate its performance using a Linux based testbed. Our experimental study reveals some performance anomalies in certain circumstances and we prove that they can be attributed to a specific design choice of PIE, namely the use of the estimated departure rate to compute the expected queuing delay. Therefore, we designed an alternative approach based on packet timestamps, implemented it in the Linux kernel and proved its effectiveness through an experimental campaign.

Excess salt intake impacts on blood pressure (BP) and the pathogenetic mechanisms of atherosclerosis predisposing to stroke and other cardiovascular disorders. The influence of salt starts early in life. Two randomized controlled trials in newborn infants suggest a direct association between dietary sodium intake and BP since the first few months of life. Newborn infants display aversion to the salt taste to develop a "preference" for salt only at age 2-3 years, in part in relation to post-natal events: this preference might be associated with later development of hypertension. The amount of sodium to be retained by an infant for proper physiological growth is largely covered by breast feeding (or low sodium formula milk) in the first six months, and later on by the gradual implementation of complementary feeding, without the need for any added salt upon food preparation. Given the lack of dose-dependence data, reference nutrient intakes (RNI) or adequate intakes (AI) for sodium have been established by national health institutions in various countries. The U.K. RNI was set at 242 mg a day for infants 0-6 months with gradual increase to 0.5 g up until age 3. The U.S. AI is somewhat lower for age 0-6 months but larger for age 1-3 years. According to a recent report, the average sodium intake in U.S. children is close to the AI up to age 2 years, to become progressively greater exceeding the Institute of Medicine recommendation later on.

To analyse the relationship of PAI-1 plasma levels to echographically determined liver steatosis and cardiometabolic risk factors in a randomly selected sample of 254 adult male participants of the Olivetti Heart Study. Accounting for age and ongoing pharmacological treatment, PAI-1 levels were directly (P < 0.005) associated with body mass index (BMI), waist circumference (WC), serum triglyceride (TG), total cholesterol, insulin, homeostasis model assessment index, gamma-glutamyl transpeptidase and peritoneal fat. At multiple linear regression (MLR) analysis, measures of adiposity and TG exerted significant and quantitatively similar effects on PAI-1 levels. A progressive rise in PAI-1 level was detected with increasing degree of steatosis. A stepwise MLR model was used to evaluate the relative power of cardiometabolic risk factors and liver steatosis on PAI-1 levels. Adjusting for alcohol intake, BMI, WC and peritoneal fat were alternatively included in the model with other variables found to be significantly associated with plasma PAI-1 level. Liver steatosis, serum TG and various indexes of adiposity each had a significant independent impact on PAI-1 plasma level and explained overall 23% of its variability. Abdominal fat, liver steatosis and serum TG levels were significant and independent determinants of PAI-1 plasma level in an unselected sample of adult male population upon adjustment for age and therapy

Development of network-sensing and congestion-control mechanisms is one of the focus topic in the modern society of information as consequence of the huge growth in types of services, data links and connectivity. A monitoring system based on hidden Markov model is proposed and implemented such to interact with distributed Internet generator. Preliminary experiments performed in a real testbed shows excellent results in the ability to manage the source-traffic generation and adapt to the channel conditions.