17,216 research outputs found
Evaluation of Time-Critical Communications for IEC 61850-Substation Network Architecture
Present-day developments, in electrical power transmission and distribution,
require considerations of the status quo. In other meaning, international
regulations enforce increasing of reliability and reducing of environment
impact, correspondingly they motivate developing of dependable systems. Power
grids especially intelligent (smart grids) ones become industrial solutions
that follow standardized development. The International standardization, in the
field of power transmission and distribution, improve technology influences.
The rise of dedicated standards for SAS (Substation Automation Systems)
communications, such as the leading International Electro-technical Commission
standard IEC 61850, enforces modern technological trends in this field. Within
this standard, a constraint of low ETE (End-to-End) latency should be
respected, and time-critical status transmission must be achieved. This
experimental study emphasis on IEC 61850 SAS communication standard, e.g. IEC
61850 GOOSE (Generic Object Oriented Substation Events), to implement an
investigational method to determine the protection communication delay. This
method observes GOOSE behaviour by adopting monitoring and analysis
capabilities. It is observed by using network test equipment, i.e. SPAN (Switch
Port Analyser) and TAP (Test Access Point) devices, with on-the-shelf available
hardware and software solutions
A novel DSM philosophy for building integrated renewable systems
This paper presents an overview of a novel concept in IT network design and power control focused on matching building integrated renewable power generation with local demands. It describes how this is achieved through combination of energy demand reduction and dynamic utilisation of embedded energy storage in a robust, efficient and cost effective manner. A brief overview of the main features of the design is given in terms of its intended benefits as an integrated system. The load components and distribution topology are described for this experimental system within the limits set by the capacity, capabilities and desired function of the network. Power supply to the network is described as including a back-up source to the photovoltaic (PV) source to add functionality and stability with no requirements for undesirable exporting of excess PV generation. The necessary configuration of the renewable array integrating with the network is also highlighted with an example compatible solar module device. A trial of the technology and demand management control in a high profile office building is described. This trial in a live working environment is providing invaluable real world data to compare against modelling and network simulation results
Web Conferencing Traffic - An Analysis using DimDim as Example
In this paper, we present an evaluation of the Ethernet traffic for host and
attendees of the popular opensource web conferencing system DimDim. While
traditional Internet-centric approaches such as the MBONE have been used over
the past decades, current trends for web-based conference systems make
exclusive use of application-layer multicast. To allow for network dimensioning
and QoS provisioning, an understanding of the underlying traffic
characteristics is required. We find in our exemplary evaluations that the host
of a web conference session produces a large amount of Ethernet traffic,
largely due to the required control of the conference session, that is
heavily-tailed distributed and exhibits additionally long-range dependence. For
different groups of activities within a web conference session, we find
distinctive characteristics of the generated traffic
Traffic measurement and analysis
Measurement and analysis of real traffic is important to gain knowledge
about the characteristics of the traffic. Without measurement, it is
impossible to build realistic traffic models. It is recent that data
traffic was found to have self-similar properties. In this thesis work
traffic captured on the network at SICS and on the Supernet, is shown to
have this fractal-like behaviour. The traffic is also examined with
respect to which protocols and packet sizes are present and in what
proportions. In the SICS trace most packets are small, TCP is shown to be
the predominant transport protocol and NNTP the most common application.
In contrast to this, large UDP packets sent between not well-known ports
dominates the Supernet traffic. Finally, characteristics of the client
side of the WWW traffic are examined more closely. In order to extract
useful information from the packet trace, web browsers use of TCP and HTTP
is investigated including new features in HTTP/1.1 such as persistent
connections and pipelining. Empirical probability distributions are
derived describing session lengths, time between user clicks and the
amount of data transferred due to a single user click. These probability
distributions make up a simple model of WWW-sessions
Critical market shares for investors and access seekers and competitive models in fibre networks
In this paper we consider and evaluate NGA architectures which meet the foreseeable future bandwidth demand and allow for highest bandwidth and quality for end-users and which no longer rely on copper cable elements. These are FTTH architectures only. From all available FTTH architectures we concentrate on the two most relevant architectures in Europe, Ethernet Point-to-Point and GPON. We assume the incumbent to be the investor in the NGA network infrastructure. If the NGA architecture is based on a Point-to-Point fibre plant we have modelled the competitors as using unbundled fibre loops as the wholesale access service. If the architecture is based on a Point-to-Multipoint fibre plant, we consider an active wholesale access (bitstream access) at the MPoP or at the core network node locations. Our basic modelling relies upon an engineering bottom-up cost modelling approach. We model the total cost of the services considered under efficient conditions, taking into account the cost of all network elements needed to produce these services in the specific architecture deployed. This approach is coherent with a Long Run Incremental Cost approach as applied in regulatory economics. Our modelling approach generates a broad set of results including the relative performance of the various network architectures, investment requirements and the degree of profitable coverage. In this paper, however, we focus on the results on the potential for competition and potential market structures in an NGA environment. --NGA architecture,cost modelling,FTTH,coverage,access models,unbundling
Applications of medical wireless LAN systems (MedLAN)
This is a post-peer-review, pre-copyedit version of an article published in Journal of Medical Marketing. The definitive publisher-authenticated version "Konstantinos A. Banitsas, R.S.H. Istepanian, Sapal Tachakra. Applications of medical Wireless LAN systems (MedLAN). Journal of Medical Marketing, Volume 2, Number 2, 1 January 2002 , pp. 136-142(7)" is available online at: http://www.ingentaconnect.com/content/pal/jomm/2002/00000002/00000002/art00008.In this paper the Wireless LAN (WLAN) networking principals are presented along with some of the implementation scenarios dedicated for Accidents and Emergencies wards. Preliminary simulation results of the MedLAN concept are also presented together with ongoing and future work in this area
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