Virtual lines, a deadlock free and real-time routing mechanism for ATM networks

In this paper we present a routing mechanism and buffer allocation mechanism for an ATM switching fabric. Since the fabric will be used to transfer multimedia traffic it should provide a guaranteed throughput and a bounded latency. We focus on the design of a suitable routing mechanism that is capable to fulfil these requirements and is free of deadlocks. We will describe two basic concepts that can be used to implement deadlock free routing. Routing of messages is closely related to buffering. We have organized the buffers into parallel fifos, each representing a virtual line. In this way we not only have solved the problem of Head Of Line blocking, but we can also give real-time guarantees. We will show that for local high-speed networks it is more advantageous to have a proper flow control than to have large buffers. Although the virtual line concept can have a low buffer utilization, the transfer efficiency can be higher. The virtual lines concept allows adaptive routing. The total throughput of the network can be improved by using alternative routes. Adaptive routing is attractive in networks where alternative routes are not much longer than the initial route(s). The network of the switching fabric is built up from switching elements interconnected in a Kautz topology

A Switch Architecture for Real-Time Multimedia Communications

In this paper we present a switch that can be used to transfer multimedia type of trafJic. The switch provides a guaranteed throughput and a bounded latency. We focus on the design of a prototype Switching Element using the new technology opportunities being offered today. The architecture meets the multimedia requirements but still has a low complexity and needs a minimum amount of hardware. A main item of this paper will be the background of the architectural design decisions made. These include the interconnection topology, buffer organization, routing and scheduling. The implementation of the switching fabric with FPGAs, allows us to experiment with switching mode, routing strategy and scheduling policy in a multimedia environment. The witching elements are interconnected in a Kautz topology. Kautz graphs have interesting properties such as: a small diametec the degree is independent of the network size, the network is fault-tolerant and has a simple routing algorithm

Virtual lines, a deadlock-free and real-time routing mechanism for ATM networks

In this paper, we present a routing mechanism and buffer allocation mechanism for an ATM switching fabric. Since the fabric will be used to transfer multimedia traffic, it should provide a guaranteed throughput and a bounded latency. We focus on the design of a suitable routing mechanism that is capable of fulfilling these requirements and is free of deadlocks. We will describe two basic concepts that can be used to implement deadlock-free routing. Routing of messages is closely related to buffering. We have organized the buffers into parallel FIFO's, each representing a virtual line. In this way, we not only have solved the problem of head of line blocking, but we can also give real-time guarantees. We will show that for local high-speed networks, it is more advantageous to have a proper flow control than to have large buffers. Although the virtual line concept can have a low buffer utilization, the transfer efficiency can be higher. The virtual line concept allows adaptive routing. The total throughput of the network can be improved by using alternative routes. Adaptive routing is attractive in networks where alternative routes are not much longer than the initial route(s). The network of the switching fabric is built up from switching elements interconnected in a Kautz topology

The Design of a System Architecture for Mobile Multimedia Computers

This chapter discusses the system architecture of a portable computer, called Mobile Digital Companion, which provides support for handling multimedia applications energy efficiently. Because battery life is limited and battery weight is an important factor for the size and the weight of the Mobile Digital Companion, energy management plays a crucial role in the architecture. As the Companion must remain usable in a variety of environments, it has to be flexible and adaptable to various operating conditions. The Mobile Digital Companion has an unconventional architecture that saves energy by using system decomposition at different levels of the architecture and exploits locality of reference with dedicated, optimised modules. The approach is based on dedicated functionality and the extensive use of energy reduction techniques at all levels of system design. The system has an architecture with a general-purpose processor accompanied by a set of heterogeneous autonomous programmable modules, each providing an energy efficient implementation of dedicated tasks. A reconfigurable internal communication network switch exploits locality of reference and eliminates wasteful data copies

Topologies for Optical Interconnection Networks Based on the Optical Transpose Interconnection System

International audienceMany results exist in the literature describing technological and theoretical advances in optical network topologies and design. However, an essential effort has yet to be done in linking those results together. In this paper, we propose a step in this direction, by giving optical layouts for several graph-theoretical topologies studied in the literature, using the Optical Transpose Interconnection System (OTIS) architecture. These topologies include the family of Partitioned Optical Passive Star (POPS) and stack-Kautz networks as well as a generalization of the Kautz and de Bruijn digraphs

Topologies for Optical Interconnection Networks Based on the Optical Transpose Interconnection System

International audienceMany results exist in the literature describing technological and theoretical advances in optical network topologies and design. However, an essential effort has yet to be done in linking those results together. In this paper, we propose a step in this direction, by giving optical layouts for several graph-theoretical topologies studied in the literature, using the Optical Transpose Interconnection System (OTIS) architecture. These topologies include the family of Partitioned Optical Passive Star (POPS) and stack-Kautz networks as well as a generalization of the Kautz and de Bruijn digraphs

Improving the representation of hydrological connectivity in conceptual models

Understanding hydrological connectivity is one of the main objectives in hydrological research. Hydrological models have been proved to be an efficient tool for a better understanding of hydrological connectivity. Conceptual models have shown certain advantages compared to physically-based distributed models in terms of data requirement and computational time. However, the hydrological connectivity in conceptual models is usually not well represented. In this study, the Soil and Water Assessment Tool (SWAT) was selected for further improvements to have a better representation and simulation of hydrological connectivity. SWAT is a semi-distributed hydrological model used to simulate the effect of land use management practices on water, sediment, and nutrient yields at a basin scale. SWAT has been tested and applied worldwide. However, the non-spatial characteristic of the hydrologic response unit (HRU) concept used in SWAT has been identified as one of the main disadvantages for modeling hydrological connectivity. In this study, the hydrologic routing subroutine of SWAT was examined and the groundwater subroutine was modified to account for hydrological connectivity in porous and karst-dominated aquifers. Results show that the current hydrologic routing subroutines of SWAT are not able to simulate hydrological connectivity between river segments in the river network. The Muskingum routing method in SWAT could (1) cause unphysical oscillations in the simulated streamflow and (2) overestimate the evapotranspiration loss in the river and results in a hydrologic disconnectivity during low flow periods. For improving the representation of hydrological connectivity in the subsurface porous aquifer, the multicell aquifer model was proposed and incorporated into SWAT. The modified model, the so-called SWAT-MCA model, was validated in two basins located in Niedersachsen, Germany. The results show that the SWAT-MCA model could well simulate the regional groundwater flow and return flow from aquifer to stream. For improving the representation of hydrological connectivity in the karst-dominated aquifer due to interbasin groundwater flow (IGF) was added to SWAT, the SWAT_IGF was developed. The developed model was applied in a karst area located in the Southwest Harz Mountains, Germany. The model was validated with the observed streamflow and spring flow. Results show that the SWAT_IGF could well represent the hydrological connection due to interbasin groundwater flow in karst areas. The modified models, SWAT-MCA and SWAT_IGF could be applied for other regions to regional groundwater flow in porous aquifer and IGF in karst-dominated aquifers

Properties and Algorithms of the KCube Interconnection Networks

The KCube interconnection network was first introduced in 2010 in order to exploit the good characteristics of two well-known interconnection networks, the hypercube and the Kautz graph. KCube links up multiple processors in a communication network with high density for a fixed degree. Since the KCube network is newly proposed, much study is required to demonstrate its potential properties and algorithms that can be designed to solve parallel computation problems. In this thesis we introduce a new methodology to construct the KCube graph. Also, with regard to this new approach, we will prove its Hamiltonicity in the general KC(m; k). Moreover, we will find its connectivity followed by an optimal broadcasting scheme in which a source node containing a message is to communicate it with all other processors. In addition to KCube networks, we have studied a version of the routing problem in the traditional hypercube, investigating this problem: whether there exists a shortest path in a Qn between two nodes 0n and 1n, when the network is experiencing failed components. We first conditionally discuss this problem when there is a constraint on the number of faulty nodes, and subsequently introduce an algorithm to tackle the problem without restrictions on the number of nodes

Can the introduction of the topographic indices in LPJ-GUESS improve the spatial representation of environmental variables?

Ecosystem modelling is an always evolving science trying to catch the complexity of the nature and its principles to model environmental responses in a realistic way. Over and over, models try to introduce more variables and interactions to achieve better representations of phenomena of interest like the responses of the ecosystem to a fast changing world (climate change, land use change). LPJ-GUESS is a flexible dynamic ecosystem model widely used to model the structure and dynamics of terrestrial ecosystems. It is based on plant physiology, biochemical cycles and feedbacks on independent gridcells, there is no consideration of lateral transfer of water between cells. On the other hand, soil moisture is essential for vegetation growth and its distribution is known to be driven by the topography of the landscape, which drives the lateral transfer of water. Based on this, it was considered important to assess the modelled spatial representation of environmental variables (soil moisture, LAI) from LPJ-GUESS and to evaluate a possible method to include the effect of topography over the hydrology in LPJ-GUESS model. For this, Alergaarde catchment (smooth relief) was chosen and by the use of correlation analysis and visual interpretation the following issues were studied, 1) Importance of topography on the spatial distribution of environmental variables based on topographic indices (Ln (Drainage area), tan ( angle slope) and topographic wetness index, TWI); 2) LPJ-GUESS ability to catch the environmental variables spatial distribution and 3) Implementation of a coupled LPJ-GUESS - topographic indices model to account for the topography influence on hydrology and assessment of its performance on modelling the spatial patterns of environmental variables. Results of the first two topics showed how LPJ-GUESS could not catch the spatial variations of satellite based LAI, and that even the gentle topography of the catchment was an important issue on explaining the heterogeneity of vegetation related variables. Nevertheless, there are many factors, like climate conditions, which affect the strength of this relationship, as reflected on low correlation coefficients (never over 0.25), the variable correlation coefficients along the year and the identification of areas more related to the topographic indexes than others. Additionally, TWI was selected, based on its higher correlations with respect to the other topographic indices, to be one used to represent the topography influence in the catchment. The integrated model, LPJ-Topographic index (LPJ-TI), use the TWI to make a cell wise characterization and create weights affecting the water inputs to the soil layer as a way to account for hydrological processes driven by topography. LPJ-TI showed localized and time dependent improvement of the spatial representation of the satellite based LAI. These results confirm the need to include the topographic influence on the hydrological module of LPJ-GUESS and present a possible low computational method to start working on.Ecosystem modelling is an always evolving science trying to catch the complexity of the nature and its principles to model the ecosystem in a realistic way. Over and over, models are being modified or complemented to make better predictions and achieve better representations of phenomena of interest like the responses of the ecosystem to a fast changing world (climate change, land use change). LPJ-GUESS is a flexible dynamic ecosystem model widely used to model vegetation, water and carbon cycles in terrestrial ecosystems. In order to model an ecosystem in LPJ-GUESS the area of interest is gridded in cells, where every cell is modelled independently; that is there is no communication between the cells so important interactions such as water movement do not occur; dynamic particularly important at watershed levels. Topography is an important driver on determining the flow of water on a catchment, thus influences de distribution of water over the area, process being evident on differential soil moisture, vegetation, vegetation growth, decomposition, etc. Topographic characteristic can be summarized on topographic indices, which aim to represent the key hydrological processes driven by topography in a simplified but realistic way. Some of the most used topographic indices related to the distribution of water over the landscape are: slope, drainage area and, a combination of former ones, the topographic wetness index. Based on the former information, the current thesis considered important to assess the modelled LPJ-GUESS distribution of the environmental variables values over the area and to evaluate a method to include the effect of topography over the hydrology in the model. For this; Alergaarde catchment, a catchment with little relief located on central Jutland Denmark, was chosen, and by the use of correlation analysis and visual interpretation of the observed and simulated spatial patterns of environmental variables (soil moisture and vegetation development represented as Leaf area index - LAI) the following issues were studied: 1) Importance of topography on the spatial distribution of environmental variables based on topographic indices (Ln (Drainage area), tan ( angle slope) and topographic wetness index, TWI); 2) LPJ-GUESS ability to catch the environmental variables spatial distribution and 3) Implementation of a coupled LPJ-GUESS - topographic indices model ( LPJ-Topographic index, LPJ-TI) to account for the topography influence on hydrology and assessment of its performance on modelling the spatial patterns of environmental variables. The coupled model, LPJ-TI, bases on making a cell wise characterization of the catchment based on giving weights to the range of values of the topographic index and using them to affect the water going into the soil layer as a way to account for hydrological processes driven by topography. Results and conclusions The results of the first two topics showed how LPJ-GUESS could not catch the spatial variations of LAI, and that even the gentle topography of the catchment was an important issue on explaining the heterogeneity of vegetation related variables. Nevertheless, it was also noticed that there are many factors (ex. weather conditions, land management activities) affecting the strength of the relationship between topography and plant development (i.e. LAI), as reflected by the low correlation coefficients (never above 0.25), stronger and lower correlation depending on the month in consideration, and the identification of areas more related to the topographic indexes than others within the same time frame. Additionally on the first topic, TWI was proven to be a good index for demonstrating the association of topography with LAI and was therefore selected to be used on the model LPJ-TI. Regarding the last issue, LPJ-TI showed localized and time dependent improvement of the spatial representation of LAI. These results confirm the need to include the topographic influence on the hydrological module of LPJ-GUESS and present a possible low computational method to start working on

A simulation assessment of the Boone River watershed: baseline calibration/validation results and issues, and future research needs

A SWAT modeling framework has been constructed for the Boone River Watershed (BRW) in north central Iowa, to support further testing of SWAT and analyses of alternative management practice and/or cropping system scenarios. The BRW covers over 237,000 ha and is an intensively cropped region dominated by corn and soybean production. Nitrate losses are of particular concern in the BRW, especially through subsurface tiles that drain the predominantly flat landscapes that persist throughout the watershed. The modeling system features an intensive set of management, land use, and soil data developed at the Common Land Unit (CLU) level. The SWAT model was tested using two different hydrologic simulation approaches for the BRW, that were based on the standard runoff curve number (RCN) option versus a new alternative RCN option available in version 2005 of SWAT. These two different approaches were used to reflect differing assumptions regarding the relative contributions of surface runoff and baseflow to the total BRW streamflow. Strong annual and monthly R2 and Nash-Sutcliffe modeling efficiency (E) statistics were found for both the 1986-1996 calibration and 1996-2006 validation periods, which ranged from 0.74 to 0.99. The R2 and E statistics determined for the calibrated annual and monthly sediment, nitrate, organic nitrogen, and total phosphorus loads for the period of 2000-2006 were also generally strong for the SWAT simulations that were performed with the standard RCN approach, ranging from 0.50 to 0.92 with most exceeding 0.70. However, the accuracy of the predicted pollutant loads generally declined when the alternative RCN approach was used, especially for the organic nitrogen estimates. The results show that specific calibration is necessary for pollutant-related input parameters for the alternative RCN approach, in order to obtain improved results. The results also show weaknesses in the overall nitrogen balance predicted for the SWAT simulations, especially for the approach based on the standard RCN method. Comparisons with historical crop yields revealed that the model underpredicted corn yields, especially for the standard RCN approach, and that there is a need to update crop parameters in SWAT to more accurately simulate current corn and soybean yields in the region