Network failures can originate from or be located in any one of several network layers as described by the OSI model. This investigation focuses on the role of physical topological design parameters in determining network reliability and performance as can be expected from the point of view of a typical client-server based connection in an Ethernet local area network. This type of host-to-host IP connection is found in many commercial, military and industrial network based systems. Using Markov modelling techniques reliability and performability models are developed for common network topologies based on the redundancy mechanism provided by IEEE spanning tree protocols. The models are tested and validated using the OPNET network simulation environment. The reliability and performability metrics calculated from the derived models for different topologies are compared leading to the following conclusions. The reliability of the entry-nodes into a redundant network is a determining factor in connection availability. Redundancy mechanisms must be extended from the entry-node to the connecting hosts to gain a significant benefit from redundant network topologies as network availability remains limited to three-nines. The hierarchical mesh network offers the highest availability (sevennines) and performability. Both these metrics can be accurately predicted irrespective of the position of the entry-node in the mesh. Ring networks offer high availability (five to sevennines) and performability if the ring remains small to medium sized, however for larger rings (N≥32) the availability is highly dependant on the relative position of the entry-node in the ring. Performability also degrades significantly as the ring size increases. Although star networks offer predictable and high performability the availability is low (four-nines) because of the lack of redundancy. The star should therefore not be used in IP networked systems requiring more than four-nines availability. In all the topologies investigated the reliability and performability can be increased significantly by introducing redundant links instead of single links interconnecting the various nodes, with the star topology availability increasing from four-nines to seven-nines and performance doubling. / MIng (Computer and Electronic Engineering), North-West University, Potchefstroom Campus, 2014

Network failures can originate from or be located in any one of several network layers as described by the OSI model. This investigation focuses on the role of physical topological design parameters in determining network reliability and performance as can be expected from the point of view of a typical client-server based connection in an Ethernet local area network. This type of host-to-host IP connection is found in many commercial, military and industrial network based systems. Using Markov modelling techniques reliability and performability models are developed for common network topologies based on the redundancy mechanism provided by IEEE spanning tree protocols. The models are tested and validated using the OPNET network simulation environment. The reliability and performability metrics calculated from the derived models for different topologies are compared leading to the following conclusions. The reliability of the entry-nodes into a redundant network is a determining factor in connection availability. Redundancy mechanisms must be extended from the entry-node to the connecting hosts to gain a significant benefit from redundant network topologies as network availability remains limited to three-nines. The hierarchical mesh network offers the highest availability (sevennines) and performability. Both these metrics can be accurately predicted irrespective of the position of the entry-node in the mesh. Ring networks offer high availability (five to sevennines) and performability if the ring remains small to medium sized, however for larger rings (N≥32) the availability is highly dependant on the relative position of the entry-node in the ring. Performability also degrades significantly as the ring size increases. Although star networks offer predictable and high performability the availability is low (four-nines) because of the lack of redundancy. The star should therefore not be used in IP networked systems requiring more than four-nines availability. In all the topologies investigated the reliability and performability can be increased significantly by introducing redundant links instead of single links interconnecting the various nodes, with the star topology availability increasing from four-nines to seven-nines and performance doubling. / MIng (Computer and Electronic Engineering), North-West University, Potchefstroom Campus, 2014

One of the local area network medium access control standards created by the Institute of Electrical and Electronic Engineers in IEEE Project 802 is the carrier sense multiple access with collision detection (CSMA/CD) medium access control. Numerous studies have been reported in the literature on the performance of CSMA/CD. These studies show that CSMA/CD performs well under light network load but not well at heavy load. To improve the performance of CSMA/CD under heavy load, a new concept called network partitioning is presented. Network partitioning allows the network to be partitioned into segments when under heavy load. Partition stations then act as bridges between the segments. The impact of network partitioning on network performance was tested using a simulation model of an Ethernet local area network (an implementation of the CSMA/CD medium access control). The simulation results show that network partitioning can improve the performance of CSMA/CD under heavy load.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / Powered by single-segment switched interconnection, Ethernet can be used in time-critical data acquisition applications. Unlike synchronous time division multiple access, asynchronous packet streams result in congestions and uncertain multiplexing delays. With the delay analysis in the worst case and probabilistic guaranteeing conditions, we restrict the packet-sizes, intervals or traffic burstiness a priori to regulate delay deviations within acceptable scales. Some methods of combinatorics and stochastic theory, e.g. Cumulant Generating Function and the Large Deviation Principle, are used and verified by some simulation-based computations. The influence of time varying delay for telemetry applications is also discussed in some sense.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Two separate imaging payloads were successfully operated using a wireless line-of-sight telemetry system that was developed as part of a recently completed UAV (unmanned aerial vehicle) imaging campaign over the largest coffee plantation in the USA. The objective was to demonstrate the performance of “off-the-shelf” wireless technology in an effort to reduce the cost of line-of-sight telemetry for imaging payloads on UAVs. Pre-deployment tests using a conventional twin-engine piloted aircraft at a flight height of 10k ft demonstrated successful broadband connectivity between a rapidly moving (ca. 280 km hr^(-1)) airborne WLAN (wireless local area network) and a fixed ground station WLAN. This paper details the performance of the wireless telemetry system on a slow-flying (<50 km hr^(-1)) solar-powered UAV at a flight height of 6.4 km.

Advanced embedded systems can consist of many sensors, actuators and processors that are deployed on one or several boards, while having a demand of interacting with each other and sharing resources. Communication between different components usually has strict timing constraints. There is thus a strong need to provide solutions for time critical communication. This thesis focuses on both the support of real-time services over standard switched Ethernet networks and the improvement of systems' real-time characteristics, such as reducing delay and jitter in processors and on communication links. Switched Ethernet has been chosen in this work because of its major advantages in industry; it supports higher bit-rates than most other current LAN (Local Area Network) technologies, including field buses, still at a low cost. We propose using a star network topology with a single Ethernet switch. Each node is connected to a separate port of the switch via a full-duplex link, thereby eliminating collisions. A solid real-time communication protocol for switched Ethernet networks is proposed in the thesis, including a real-time layer between the Ethernet layer and the TCP/IP suite. The network has the capability of supporting both real-time and non real-time traffic and assuring adaptation to the surrounding protocol standards. Most embedded systems work in a dynamic environment, where the precise behavior of the network traffic can usually not be predicted. To support real-time services, we have chosen the Earliest Deadline scheduling algorithm (EDF) because of its optimality, high efficiency and suitability for being used in adaptive schemes. To be able to increase the amount of guaranteed real-time traffic, the notion of Asymmetric Deadline Partitioning Scheme (ADPS) is introduced. ADPS allows distribution of the end-to-end deadline of a message, sent from any source node in the network to any destination node via the switch, into two sub-deadlines, one for each hop according to the load of the physical link that it must traverse. For the EDF scheduling algorithm, the feasibility test is one of the most important techniques that provides us with information about whether or not the real-time traffic can be guaranteed by the network. With the same computational complexity as the feasibility test, a method has been developed to compute the minimum EDF-feasible deadline for a real-time task. The importance of this method in real-time applications lies in that it can be effectively used to reduce the response times of specific control activities or limit their input-output jitter. To allow more flexibility in the control of delay and jitter in real-time systems, a general approach for reducing task deadlines according to the requirements of individual tasks has been developed. The method allows the user to specify a deadline reduction factor for each task in order to better exploit the available slack according to the tasks' actual requirements. / <p>Ingår även i serien: Technical report. D / Department of Computer Science and Engineering, Chalmers University of Technology, 1653-1787 ; 28</p>

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / This paper evaluates the performance as well as effectiveness of the High Speed Ethernet LANBased Distributed Telemetry Data Network Architecture. It also attempts to obtain a feasible solution for the Extension of LAN over High Performance Digital Modem via Routers and Bridges. With the advent of highly efficient broadband TCP/IP network and rapid growth of data traffic demand in the area of Telemetry Data Acquisition and Processing, one has to adopt a high bit rate PCM Telemetry Data Stream with the strategy of distributed task scheduling in multiprocessor environment. The proposed Telemetry System Architecture is adopted as a milestone to Modern Telemetry system. It incorporates various value added services for the performance evaluation of various flight vehicles providing authenticated data. This paper shows that by configuring the IP addresses of various nodes and router / bridges with V.35 interfaces, it is possible to extend the Telemetry Data on a local LAN to the remote LAN for display and high speed processing in real time. Necessary comparisons of performance of the existing to the proposed systems are presented.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / At the 2007 iNet Technology Demonstrator multiple vendors are asked to participate to develop and evaluate protocols for time synchronization, configuration identification and heterogeneous data packet transfer. The iNet initiative from RCC is aimed at focusing and collating telemetry network developments within the wider sphere of commercial and military network developments. The KAM-500 is an inherently networked data-acquisition system offering seamless gateways to many heterogeneous data sources, such as different sensor devices, avionics-busses, networks and video sources. This paper offers insights into the impact of traffic and network configuration on the performance of heterogeneous data acquisition in a homogenous-switched network based a 1588 enabled controller module.

International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California / The Data Acquisition, Analysis, and Simulation System (DAAS) is a computer system designed to allow data sources on spacecraft in the Flight System Testbed (FST) to be monitored, analyzed, and simulated. This system will be used primarily by personnel in the Flight System Testbed, flight project designers, and test engineers to investigate new technology that may prove useful across many flight projects. Furthermore, it will be used to test various spacecraft design possibilities during prototyping. The basic capabilities of the DAAS involve unobtrusively monitoring various information sources on a developing spacecraft. This system also provides the capability to generate simulated data in appropriate formats at a given data rate, and to inject this data onto the communication line or bus, using the necessary communication protocol. The DAAS involves Serial RS232/RS422, Ethernet, and MIL-STD-1553 communication protocols, as well as LabVIEW software, VME hardware, and SunOS/UNIX operating systems.

ITC/USA 2015 Conference Proceedings / The Fifty-First Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2015 / Bally's Hotel & Convention Center, Las Vegas, NV / Northrop Grumman Corporation's B-2 Flight Test Instrumentation team is revamping its entire Data Acquisition System (DAS) to be an Ethernet based network (EBN) system that will provide simplified wiring, higher speeds, greater capacity, and control over the data. The old system became obsolete in terms of capability and maintainability. New on-board avionic systems also demand that the Flight Test Instrumentation group (INSTR) accommodate fiber and high speed Ethernet data. In addition, the footprint and location for INSTR systems and components will be moved to remote areas. INSTR engineering selected the Teletronics Technology Corporation's Ethernet networked Data Acquisition Units (DAUs), known as MnDAUs, as the core system. Prior to the first flight utilization of the new INSTR DAS will undergo extensive lab and field testing to assure flight test effectiveness and the accuracy of all necessary data products. The goal is to acquire and employ the best system available while avoiding costly lessons.