Link-level Data Research Articles

A complete architecture for Ambient Assisted Living scenarios using a cross protocol proxy

Nowadays, in the most developed countries, modern society is moving towards scenarios in which the self-sufficiency elderly people live alone in their homes. An automatic remote monitoring system using wearable sensors is becoming even more important in Ambient Assisted Living applications. For this type of services, it is important that IoT sensors networks, which are generally composed of devices with limited computing power and storage, implement reliable communication among sensors and the Internet. There are several specialized protocols for the Internet of Things proposed by the scientific community, each characterized by its own levels of Quality of Services. The emergence of new protocols forces the need for developing proxying systems able to intermediate among different types of networks and to translate the relative protocols. In this paper, we propose a complete architecture for monitoring and managing wearable devices, and, in particular, fall detection ones. Our system uses a cross protocol proxy and a device with CoAP and MQTT as application level protocols, while it exploits the NB-IoT at physical and data-link levels. The goal of this work is the performance evaluation of the proposed solution in terms of Throughput, Round Trip Time and Delay. The results highlight the low latency reached by the proposed system architecture thanks to the implemented protocols.

Evaluation of Posted Speed Limits Reductions on Urban Roads with a High Percentage of Cyclists

This paper presents a before and after analysis of the impact of posted speed limit (PSL) changes on passenger car (FHWA class 2 vehicle) speeds in Portland, Oregon. The study focuses on urban roads, comparing sites that underwent a PSL 5-mph reduction (treatment sites) and sites where the PSL did not change (control sites). Sites with a high percentage of and priority for cyclists (neighborhood greenways) and sites with a more standard traffic composition were compared. Differences in speed characteristics such as mean and 85th percentile speeds, the speed variance, and the proportion of vehicles exceeding a speed threshold (relative to the PSL) were evaluated on aggregate and individual scales. A series of statistical hypothesis tests were employed to assess changes in the speed characteristics among individual data set pairs. The results suggest distinct differences between the treatment and control groups and neighborhood greenway and non-greenway sites. Although there is a high degree of variability, the treatment group experienced more decreases in the speed characteristics, and by a greater amount than the control group, on average. Within the treatment group, sites with a priority for cyclists were even more likely to experience a larger reduction in operating speeds. These results could be interpreted as link-level data providing indirect yet supporting evidence for the safety in numbers hypothesis and changes in motorists’ behavior on neighborhood greenways.

Development of a model of a subsystem for forecasting changes in data transmission routes in special purpose mobile radio networks

This research addressed the issue of improving the quality of service for the control system of mobile radio networks. The analysis of the forecasting sphere concerning the methods of service quality of mobile radio networks for special purposes, in particular, forecasting the time of congestion of data transmission routes is carried out. It is found that these methods are used in wired and computer networks operating at the network and data link levels. The basic parameters of the protocols of the channel and network layers of mobile radio networks are highlighted. Forecasting methods are analyzed: temporal extrapolation, causality, expert, and the main disadvantages are indicated. A model of a control system for mobile radio networks with a forecasting subsystem is shown. The features of mobile radio networks, which form the requirements for routing methods, are described. A lot of requirements have been put forward for the model of a control system for mobile radio networks. The structure of a model of a control system for mobile radio networks with an improved forecasting subsystem is proposed. On the basis of genetic algorithms, the tasks that arise in the process of identification, training and forecasting in the forecasting subsystem are solved. The operation of the processes consists in building a base of rules aimed at identifying significant dependencies in a time series based on the use of a genetic algorithm. It is based on the use of evolutionary principles to find the optimal solution. Application of the proposed model will allow real-time identification and will significantly improve the quality of service for mobile radio networks. It will increase the speed and volume of data processed during training, improve the quality and reliability of predicting changes in data transmission routes

Sharing of Copper Pairs for Improving DSL Performance in FTTx Access Networks

In this paper, we analyze two techniques allowing to significantly improve the bit rate per user in the current and future FTTx access networks. They are based on the possibility of sharing copper pairs at data link level among subscribers served by the same distributor. Sharing can be achieved by inserting low-cost devices in the current FTTx access networks. In particular, as shown in this paper, sharing of copper pairs is obtained according to two different approaches. The first approach considers the possibility of increasing bit rate by a radio-shared channel that can be accessed locally by all authorized customer premises equipments (CPEs) inside the building(s). The system providing radio access is connected to the DSLAM by means of extra and temporarily unused copper pairs in the main cable connecting the DSLAM to the distributor. The second approach considers the possibility of inserting an active transceiver device in the current passive distributor(s) bridging the DSLAM to the CPEs. Depending on the activity of CPEs connected at the same distributor, results show that both the solutions allow to achieve very high downstream bit rates per user (about 800 Mb/s at 100 m with 50% CPE activity). Devices to be inserted in the FTTx network can be realized using electronic components currently available on the market.

Methods and technologies for computer networks protection (the physical and data link layers)

Standard solutions that are supported by manufacturers of equipment for computer networks (switches the 2nd and 3rd levels, routers), implemented in the operating systems and protocols, and can be used for the development and implementation of integrated corporate network protection systems are considered in this article. The article is the first of a series of articles devoted to the analysis of methods and technologies of protection. The typical threats to computer network at the physical (physical damage of the data channels, unauthorized changes in the functional environment, disabling physical data channels, setting noise over the entire bandwidth of the channel) and data link (the generation of broadcasting frames to overload the data channels and switching equipment, the substitution of nodes MAC address, attacks on ARP and Spanning-Tree protocols) layers of OSI model are given and the features of methods and technologies to protect are analyzed. The features of use of limited and unlimited signal transmission media in terms of information security are considered at the physical level and a number of additional measures top prevent unauthorized changes in the functional medium networks are given (such as: the limitation of physical access to cable channels, switching nodes and data centers, the development and implementation of a policy of remote access to network equipment, deployment of auxiliary video surveillance and access control systems, redundancy of the most critical channels, network devices and servers). At the data link layer are analyzed such functions of switches as Port security, DHCP Snooping, Dynamic ARP Inspection, IP Source Guard; segmenting the network into separate zones using the technology of Virtual Local Area Network to broadcast restrictions and improving information security; implementation of network access control system with authentication and authorization at the data link layer. To implement the access control systems of the channel level the features of the 802.1x protocol are considered and its main disadvantage (the lack of data encryption, which may lead to data interception and the implementation of DoS attacks) is determined. To build more secure solutions are proposed to use the combination of IPSec and 802.1x or new IEEE 802.1AE protocols (MACsec protocols that solve privacy and data integrity problems) and the IEEE 802.1AR standard, which defines a unique secure device identifier for their authorization. Analysis of methods and protection technologies at the physical and data link levels of the OSI model which was conducted in work allows making informed decisions about choosing methods to protect networks for different purposes and with different requirements regarding data protection.References 17, Tables 1.

An analytics approach to dis-aggregate national freight data to estimate hazmat traffic on rail-links and at rail-yards in Canada

Numerous research initiatives have been undertaken in the risk assessment and risk management of rail hazardous materials (hazmat) transportation. However, the true benefits could not be demonstrated because of the absence of rail-link and rail-yard level information about hazmat volume. We propose an analytics based methodology to estimate yard and link level data, which is applied to the railroad network in Canada. The proposed methodology was used to solve numerous problem instances for the three chosen classes of hazmat responsible for moving over 80% of hazmat shipments in Canada. The exercise enabled us to identify the hot-spots in the railroad network, to examine the changes in the volume-based ranking of various rail-yards and rail-links as a result of geographical shifts in hazmat supplies over the next decade, and to investigate the impact of new pipeline projects on rail crude oil shipments.

Transmission Power Control for Link-Level Handshaking in Wireless Sensor Networks

In practical wireless sensor networks (WSNs), the main mechanism for link-level data exchange is through handshaking. To maximize the network lifetime, the transmission power levels for both data and acknowledgement (ACK) packets should be selected optimally. If the highest transmission power level is selected then the handshake failure is minimized, however, minimizing handshake failure does not necessarily result in the maximized lifetime due to the fact that for some links selection of the maximum transmission power may not be necessary. In this paper, we investigate the impact of optimal transmission power assignment for data and ACK packets on network lifetime in WSNs. We built a novel family of mathematical programming formulations to accurately model the energy dissipation in WSNs under practical assumptions by considering a wide range of energy dissipation mechanisms. We also investigate the validity of a commonly made assumption in wireless communication and networking research: lossless feedback channel (i.e., ACK packets never fail). Our results show that the global optimal assignment of data and ACK packets can be replaced with link scope power level assignment strategies without any significant deterioration of network lifetime. The assumption that ACK packets do not fail is shown to be misleading.

Role of Unidirectionality and Reverse Path Length on Wireless Sensor Network Lifetime

Transceiver characteristics, asymmetric interference, and various properties of electromagnetic propagation environment create unidirectional links in wireless sensor networks (WSNs), especially in extreme environments. Utilization of unidirectional links is shown to improve network connectivity and lifetime. In practical WSNs, link level data exchange is performed through handshaking. However, a special handshake mechanism, where acknowledgment (ACK) packets are conveyed through a multihop reverse path, is necessary to be able to utilize unidirectional links. In this mechanism, hop length of the reverse path is a key design parameter because by allowing longer reverse paths, more unidirectional links can be utilized. However, increasing the reverse path hop length increases the energy overhead due to the extra ACK packets. Furthermore, complexity of maintaining the data flow also increases as the allowed maximum reverse path hop length increases. In this paper, we seek the answer for the following question: what is the optimum number of hops allowed for the reverse path hop length in WSNs? We created a novel mixed integer programming (MIP) framework to characterize the impact of reverse path hop length on WSN lifetime and performed extensive numerical analysis. Our results show that reverse path hop length has a significant impact on WSN lifetime.

Exploiting data link layer features to realize communication models in FieldBus system

The high complexity of actual process control systems in factory automation has led to the need of suitable communication systems to interconnect field and control devices, in order to overcome most of the limits of the actual point-to-point connections. Serial communication systems known as FieldBuses represent a valid solution to these problems. At present the IEC/ISA FieldBus protocol, which is currently being standardized, represents an international standard for process control networks. Although the standard has been almost completely defined, it is still considerably difficult to understand, above all as regards implementation of the communication models offered by the Application layer through the access medium mechanisms available at the Data Link level. This mapping is a key point in the definition of a standard, as only correct mapping between application layer communication models and data link layer mechanisms can guarantee that all the time-critical requirements of application processes will be fully met. The aim of this paper is mainly to analyze the communication models currently offered by the Application layer and their implementation through the mechanisms present in the Data Link layers. The results of the analysis will show that the models currently offered by the standard are insufficient for the implementation of certain realistic process control system scenarios. In order to bridge the gaps pointed out, the paper proposes a further communication model, specifying its implementation through the Data Link mechanisms.

Students as multimedia composers

This study is distinguished by distancing itself from the type of multimedia research that looks at the effects of multimedia instructional units on students. The approach, instead, is within a constructionist learning paradigm and the research task is to take the first steps to begin to know what we don't know about the student creation of multimedia documents. The outcome of preliminary research on the use of MediaText, a multimedia composition tool, with high school students across several disciplines indicates from an analysis of document level and link level data on 62 student-produced multimedia documents across individual students and assignments that students unfamiliar with multimedia tend to apply their existing writing skills to produce annotated text rather than integrated compositions, in which the links are clearly part of the structure of the data.

Control protocol and its performance analysis for distributed ATM virtual path self-healing network

A restorable network comprised of a mesh of ATM virtual paths (AVPs) is expected to be superior to distributed SONET digital cross-connect self-healing networks in terms of restoration time. The paper presents a reliable protocol and evaluation of its performance for control information transfer in distributed AVP self-healing networks. Two error-recovery technologies for the data-link level (selective retransmission and go-back-N) in AVP networks are reviewed, and a model for evaluating the delay of the go-back-N method that has been used in existing terrestrial systems is derived analytically. The proposed analytic model is combined with a self-healing simulator for AVP mesh networks to evaluate the restoration time characteristics. Case study results for the worst-case scenario show that the total restoration time, including link-by-link error control for self-healing control messages, is expected to be less than 2 s, which is the time objective for complete restoration for a metropolitan LATA network. The results also show that the estimated average delay penalty for adding the link-by-link error recovery process is 7.5 ms for complete service restoration. >

PAT: A protocol analysis tutor

A computer-aided learning package, PAT (protocol analysis tutor), developed as a tool to help students and novice data communications engineers learn the basic concepts of data link protocols, is described. The tool enables users to construct the frames of the HDLC (high-level data link control) standard data-link level protocol. The frames can be combined in sequence to form a call, representing the execution of the protocol. At all stages, checks of both the syntax and semantics of the call are made.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

MPEG++: A robust compression and transport system for digital HDTV

This paper provides a technical overview of MPEG++, a robust video compression and transport system for digital HDTV. MPEG++ forms the basis of ‘Advanced Digital Television’ (ADTV), the all-digital terrestrial simulcast system currently under development by the Advanced Television Research Consortium (ATRC). ADTV incorporates an efficient MPEG-compatible compression algorithm at its central core, with application-specific data prioritization and transport features added as separable layers. The compression process is based on a 1440×960 (1050-line 2: 1 interlaced) HDTV format, producing a selectable bit-rate in the region of 15–20 Mbit/s. The data priorization layer of MPEG++ achieves robust delivery over an appropriate two-tier modem by separating compressed video data into high- and standard-priority bitstreams with appropriate bit-rates. This priorized data is then formatted into fixed length ‘cells’ (packets) with appropriate data-link level and service-specific adaptation level headers, designed to provide capabilities such as flexible service multiplexing, priority handling, efficient cell packing, error detection and graceful recovery from errors. An outline of each of the above MPEG++ elements (i.e., compression, prioritization and transport) is given, and is followed by a description of a software model for the system. Simulation model based performance results which illustrate MPEG++ image quality and robustness are briefly reported.

TheUNIXSystem: The Virtual Protocol Machine

The UNIX™ operating system Virtual Protocol Machine (VPM) is a package of software tools that allows a wide variety of link-level data communications protocols to be implemented efficiently in a high-level language. The resulting protocol implementations are independent of the particular communications hardware, the host machine architecture, and the host operating system, and therefore can be ported easily from one hardware/software environment to another. An extension to VPM, the Common Synchronous Interface (CSI), provides similar benefits for the higher-level protocol software that runs in the UNIX system host. The implementations of VPM use Programmable Communications Devices (PCDs) to off load the link-level communications processing from the host CPU. A high-level language protocol description is translated by a protocol compiler that runs on the host machine. The resulting module is then loaded into the PCD and executed. The other components of VPM are a transparent protocol driver that allows user processes to interact directly with a link-level protocol implementation, a realtime trace capability to facilitate debugging, and several utility programs. VPM has been implemented on several different PCDs and several types of host computers. VPM-based protocol implementations can be ported with little or no change from one VPM implementation to another. VPM and CSI greatly reduce host system overhead while producing maximum communications throughput. A number of different higher-level protocols and their link-level counterparts have been implemented in the UNIX system using CSI and VPM; among them are X.25, 3270 emulation, a synchronous terminal interface, and a facility for remote job entry to IBM hosts.

Banet — a local area network for distributed data processing

A broadcast architecture network (Banet) suitable for distributed data processing is proposed. One feature of Banet is that the broadcast-within-a-group function is supported not only by the datalink level but by the transport or session-level network structure. The commitment control scheme is included in the network protocol. Design goals, physical structure and protocols are discussed.