Buffer Management

Femtocells deployment has become a new paradigm in improving the mobile network’s services for indoor users, by providing better data rates and coverage. Femtocells deployment results to a heterogeneous network that requires two layers of utilization of the available radio resources and this leads to interference. Despite the improvements brought about by the zero-power ABS time domain technique, it suffers reduced throughput of femtocell users in a femto-macro heterogeneous network. A method used in this research to address this limitation was the reduced-power ABS time domain technique that mitigated interference. A comparison was made between the two schemes and it was found that the reduced-power ABS scheme provided higher throughput to femtocell users when muting ratios of 0, 0.3, 0.5 and 0.8 were used. The results obtained achieved optimal and fair overall performance. This research centered on communication in the downlink direction only .

In today's highly competitive manufacturing landscape, optimizing job shop scheduling has become vital for maximizing operational efficiency and minimizing production delays. This study explores the dual challenge of makespan minimization and efficient buffer management within job shop environments. By integrating a hybrid metaheuristic approach combining Genetic Algorithm (GA) and Particle Swarm Optimization (PSO), we propose an intelligent scheduling framework that not only reduces the overall makespan but also enhances the utilization of intermediate buffers across machines. The experimental results, validated through benchmark datasets and real-time shop floor simulations, demonstrate significant improvements in throughput, machine utilization, and flow consistency. Our approach outperforms traditional heuristics by dynamically adjusting buffer capacities and job sequencing based on system feedback, paving the way for more resilient and adaptive manufacturing operations.

Emerging application domains such as interactive vi- sion, animation, and multimedia collaboration display dy- namic scalable parallelism, and high computational re- quirements, making them good candidates for executing on parallel architectures such as SMPs or clusters of SMPs. Apart from their main algorithmic components, these ap- plications need specialized support mechanisms that en- able plumbing different modules together, cross module

In this paper we present experimental results evaluating the performance and fairness of FAST TCP in a series of tests involving realistic low rate network access scenarios. Links both using the DOCSIS cable modem medium access control (MAC) cable modem and simple low rate links were investigated. We seek to compare our expectations from theory with the behavior of an actual access network implementation.

The SHRIMP multicomputer provides virtual memory-mapped communication (VMMC), which supports protected, user-level message passing, allows user programs to perform their own buffer management, and separates data transfers from control transfers so that a data transfer can be done without the intervention of the receiving node CPU. An important question is whether such a mechanism can indeed deliver all of the available hardware performance to applications which use conventional message-passing libraries.This paper reports our early experience with message-passing on a small, working SHRIMP multicomputer. We have implemented several user-level communication libraries on top of the VMMC mechanism, including the NX message-passing interface, Sun RPC, stream sockets, and specialized RPC. The first three are fully compatible with existing systems. Our experience shows that the VMMC mechanism supports these message-passing interfaces well. When zero-copy protocols are allowed by the seman...

This paper examines how VI-based interconnects can be used to improve IIO path performance between a database server and the storage subsystem. We design and implement a software layer, DSA, that is layered between the application and VI. DSA takes advantage of specific VI features and deals with many of its shortcomings. We provide and evaluate one kernel-Ievel and two user-Ievel implementations of DSA. These implementations trade transparency and generality for performance at different degrees, and unlike research prototypes are designed to be suitable for realworld deployment. We present detailed measurements using a commercial database management system with both micro-benchmarks and industrial database workloads on a mid-size, 4 CPU, and a large, 32 CPU, database server. Our results show that VI-based interconnects and userlevel communication can improve all aspects of the 1/0 path between the database system and the storage back-end. We also find that to make effective use of VI in 1/0 intensive environments we need to provide substantial additional functionality than what is currently provided by VI. Finally, new storage APIs that help minimize kernel involvement in the 1/0 path are needed to fully exploit the benefits of VI-based communication. Because VI does not deal with a number of issues that are important for storage applications, we design a new blocklevel 1/0 module, DSA (Direct Storage Access), that is layered between the application and VI (Figure ). DSA uses a custom protocol to communicate with the actual storage server, the details of which are beyond the scope of this paper. DSA takes advantage of specific VI features and addresses many of its shortcomings with respect to 1/0-1

Cellular IP networks deal with the concepts of micro-mobility. Buffer management in Cellular IP networks is very crucial as its proper usage not only increases the throughput of the network but also results in the reduction of the call drops. This article proposes a model for buffer management in Cellular IP network using Particle Swarm Optimization (PSO), an evolutionary computational method often used to solve hard problems. The model considers two kinds of buffers; Gateway buffer and Base Station buffer. In the proposed two-tier model, the first tier applies a prioritization algorithm for prioritizing real-time packets in the buffer. In the second tier PSO algorithm is used on a swarm of cells in the network. PSO is applied for a given time slot, called window. In each window period the swarm can store number of packets depending on the window size and the total number of packets. The effect of various parameters e.g. number of packets, size of packets, window size, and a thresho...

Much computational power on state-of-the-art multicomputers like the Paragon is wasted with porting applications. Using networks of workstations is an attempt to withdraw this workload from multicomputer systems. Therefore an environment is needed which provides the programming interface of multicomputers on coupled workstations. The paper describes the design and implementation of the NXLib environment which allows to use Ethernet coupled workstations as a development platform for applications targeted for Intel Paragon systems. A drawback of multicomputers is that porting existing applications onto those systems often requires enormous e orts. Applications have to be parallelized which leads to frequent test runs during the implementation. Therefore, much workload on multicomputer systems consists of test and debugging runs. To withdraw some of this load, an environment is needed which allows the implementation of applications for multicomputer systems on di erent hardware platforms. Today, typical environments in universities and companies consist of several networked workstations. The basic architecture of multicomputer systems and coupled workstations is similar: independent processing elements (nodes or workstations) which are interconnected. In di erence to the multicomputers' high performance interconnection network, workstations currently use a slower interconnect. In addition the network has to be shared with other machines and users which are also connected to the network. State-of-the-art multicomputers like the Paragon o er a proprietary message passing environment. An implementation of that library on coupled workstations would allow for using interconnected workstations as a development platform for applications where the production code should nally run on a multicomputer ? This project was partially funded by a research grant from the Intel Foundation.

The behavior of IP based network traffic has been the subject of several works. In this paper we compare two modeling approaches and their ability to capture two basic traffic features: packet size distribution and interarrival times. Data traces have been measured at the border gateway of the campus network of the University of Pavia at different times of the day. The two modeling schemes use respectively well established Hidden Markov Model (HMM) techniques and a stochastic engine derived from chaotic attractors.

In this paper we propose a communication benchmark suite: BTU(Bits To the User). In the BTU benchmarking process, the vendor supplies a workstation running a UNIX* operating system, we install our benchmark program and connect the workstation to a testbed which emulates a LAN/WAN environment. The benchmark run will submit the workstation to a carefully designed combination of tests. The result is a predictor of what the user, at the application level, can expect in terms of bits sent to or received from a remote host. Our benchmark takes into account concurrent activities such as CPU and I/O activities which compete for resources 011 the test machine. The combination of these activities and concurrent activities on the network will interfere with the test machine's communication performance. The automated BTU benchmark test suite produces results at various levels of abstractions ranging from a single number, characterizing average performance in the style of SPEC92, to a TCP time sequence chart for abnormal behaviors. We intend to serve the user of a workstation by providing information which should enable the users to make a reasonable judgment when acquiring a workstation with a specific configuration within certain cost constraints. Our results when used along with existing benchmarks will make a powerful combination for predicting overall performance. Neither price nor SPECmarks are as good a predictor of communication performance as that measured by BTUs. We conclude this paper with a discussion of extensions to faster *TM of US/' , Inc.

We propose a new space priority mechanism, and analyze its performance in a single Constant Bit Rate (CBR) server. The arrival process is derived from the superposition of two types of traffics, each in turn results from the superposition of homogeneous ON-OFF sources that can be approximated by means of a two-state Markov Modulated Poisson Process (MMPP). The buffer mechanism enables the Asynchronous Transfer Mode (ATM) layer to adapt the quality of the cell transfer to the Quality of Service (QoS) requirements and to improve the utilization of network resources. This is achieved by "Selective-Delaying and Pushing-In" (SDPI) cells according to the class they belong to. The scheme is applicable to schedule delay-tolerant non-real time traffic and delaysensitive real time traffic. Analytical expressions for various performance parameters and numerical results are obtained. Simulation results in term of cell loss probability conform with our numerical analysis.

Flash memory has characteristics of out-of-place update and asymmetric I/O latencies for read, write, and erase operations. Thus, the buffering policy for flash-based databases has to consider those properties to improve the overall performance. This article introduces a new approach to buffer management for flash-based databases, called AD-LRU (Adaptive Double LRU), which focuses on improving the overall runtime efficiency by reducing the number of write/erase operations and by retaining a high buffer hit ratio. We conduct trace-driven experiments both in a simulation environment and in a real DBMS, using a real OLTP trace and four kinds of synthetic traces: random, read-most, write-most, and Zipf. We make detailed comparisons between our algorithm and the best-known competitor methods. The experimental results show that AD-LRU is superior to its competitors in most cases.

The buffer pool manager is a central component of ADABAS, a high performance scaleable database system for OLTP processing. High efficiency and scalability of the buffer pool manager is mandatory for ADABAS on all supported platforms. In order to allow a maximum of parallelism without facing the danger of deadlocks, a multi-version locking method is used. Partitioning of central data structures is another key to performance. Variable page sizes allow for flexible tuning, but make the buffer pool logic more sophisticated, in particular concerning parallelism.

With the advent of large-scale parallel computing systems, making parallel programs fault-tolerant becomes an important problem, be- cause the probability of a failure increases with the number of proces- sors. In this paper, we describe a very simple scheme for rendering a class of ...

Mechanisms for managing message buffers in Time Warp parallel simulations executing on cache-coherent shared-memory multiprocessors are studied. Two simple buffer management strategies called the sender pool and receiver pool mechanisms are examined with respect to their efficiency, and in particular, their interaction with multiprocessor cache-coherence protocols. Measurements of implementations on a Kendall Square Research KSR-2 machine using both synthetic workloads and benchmark applications demonstrate that sender pools offer significant performance advantages over receiver pools. However, it is also observed that both schemes, especially the sender pool mechanism, are prone to severe performance degradations due to poor locality of reference in large simulations using substantial amounts of message buffer memory. A third strategy called the partitioned buffer pool approach is proposed that exploits the advantages of sender pools, but exhibits much better locality. Measurements of this approach indicate that the partitioned pool mechanism yields substantially better performance than both the sender and receiver pool schemes for large-scale, small-granularity parallel simulation applications. The central conclusions from this study are: (1) buffer management strategies play an important role in determining the overall efficiency of multiprocessor-based parallel simulators, and (2) the partitioned buffer pool organization offers significantly better performance than the sender and receiver pool schemes. These studies demonstrate that poor performance may result if proper attention is not paid to realizing an efficient buffer management mechanism.

As buffer cache is used to overcome the speed gap between processor and storage devices, performance of buffer cache is a deciding factor in verifying the system performance. Need of improved buffer cache hit ratio and inabilities of the Least Recent Used replacement algorithm inspire the development of the proposed algorithm. Data reuse and program locality are the basis for determining the cache performance. The proposed algorithm determines the temporal locality by detecting the access patterns in the program context from which the I/O request are issued, identified by the program counter signature, and the files to which the I/O request are addressed. For accurate pattern detection and enhanced cache performance re-reference behavior exploited in the cache block are associated with unique signature. Use of multiple caching policies is supported by the proposed algorithm so that the cache under that pattern can be best utilized.

In recent times, the data generation and storage modules in several organizations have seen a shift from the centralized approach to a parallel and distributed architecture. Also, the nature of data is changing from the static tables in databases and data warehouses to continuous stream data in data stores used for various technical and business applications. In such times, it is necessary to have data mining systems which accept data generated independently at disparate sites and perform mining at the local sites as well as at the global level at a centralized location. This paper describes a complete system to handle continuous stream data at parallel sites, the memory management involved in the storage of this data and an algorithm specifically designed to perform association rule mining in such an environment.

We consider the problem of interconnecting low speed LANs over a high-speed shared-memory ATM switch. A bottleneck is formed when more than one source originate traffic to the same destination LAN. In this case, a congestion may be created at the output gateway (destination LAN interface) and the required services are interrupted. In this paper we propose a new integrated scheme for call admission (CAC) and buffer management. The objective of the scheme is to prevent the congestion at the destination LANs, as well as within the ATM switch, while minimizing connection rejection rates (maximizing the utilization of the ATM switch). The scheme uses two types of parameters: first, the connection parameters which are estimated at the network interface unit and specified during connection set-up, and second, the actual traffic characteristics and buffer requirements. Therefore, the proposed scheme combines both parameter-based and measurement-based approaches to the problems of call admission and congestion control. The proposed scheme is shown not to require intensive computations and can be implemented in real time in a high-speed ATM switch. A simulation model for the system is developed from which the performance of our integrated CAC and buffer management scheme is evaluated. It is shown that the application of our CAC criteria maintains cell/packet dropping to within the same order of magnitude. It is also shown that using virtual buffer allocation, in conjunction with our CAC criteria, results in almost no cell/packet dropping. ᭧ 1998 Elsevier Science B.V.

Climate change, rapid urbanization, and population growth have intensified global water scarcity, increasing reliance on groundwater resources. One of the most effective solutions to this crisis is artificial groundwater recharge through floodwater harvesting, which captures surface runoff and facilitates controlled infiltration into aquifers. Floodwater harvesting techniques, such as check dams, recharge basins, and injection wells, are designed to capture and store excess runoff, allowing controlled percolation and groundwater replenishment. This study provides a comprehensive review of artificial groundwater recharge techniques, categorizing them into surface (spreading), sub-surface, and indirect methods. A total of eleven techniques were analyzed, including recharge basins, check dams, injection wells, and induced recharge methods, which have been successfully implemented in various regions. The review highlights the benefits of artificial recharge, such as improved groundwater storage, reduced soil erosion, and enhanced water quality. However, challenges such as aquifer contamination, sediment clogging, and inefficient recharge structures remain significant barriers to implementation. The study also examines the environmental impacts of artificial recharge, addressing both positive aspects (such as ecological restoration and energy savings) and potential drawbacks (including land subsidence and aquifer pollution risks). A special focus is given to Egypt, where floodwater harvesting has been implemented in Sinai using check dams and surface recharge techniques. Despite its potential, groundwater recharge in Egypt remains underutilized, necessitating further research into sub-surface recharge methods and alternative energy solutions such as solar-powered recharge systems. The findings

Vehicular Delay-Tolerant Networking (VDTN) is a Delay-Tolerant Network (DTN) based architecture concept for transit networks, where vehicles movement and their bundle relaying service is opportunistically exploited to enable non-real time applications, under environments prone to connectivity disruptions, network partitions and potentially long delays. In VDTNs, network resources may be limited, for instance due to physical constraints of the network nodes. In order to be able to prioritize applications traffic according to its requirements in such constrained scenarios, traffic differentiation mechanisms must be introduced at the VDTN architecture. This work considers a priority classes of service (CoS) model and investigates how different buffer management strategies can be combined with drop and scheduling policies, to provide strict priority based services, or to provide custom allocation of network resources. The efficiency and tradeoffs of these proposals is evaluated through extensive simulation.

Pointer swizzling improves the performance of OODBMSs by reducing the number of table lookups. However, the object replacement incurs the unswizzling overhead. In this paper, we propose a new pointer swizzling strategy, the dynamic indirect pointer swizzling (DIPS). DIPS dynamically applies pointer swizzling techniques in order to reduce the overhead of unswizzling. DIPS uses the temporal locality information which is gathered by the object buffer manager. The information is used to select the object to whose pointers the pointer swizzling techniques are applied and to dynamically bind the pointer swizzling techniques using the virtual function mechanism. We show the efficiency of the proposed strategy through experiments over various object buffer sizes and workloads.

In spite of the larger performance gain such as higher throughput and almost zero packet retransmissions compared to TCP Reno, TCP Vegas still has a few obstacles for it to be deployed in the Internet. Studies have shown unfair treatment to Vegas connections when they compete with Reno connections. Other issues identified with TCP Vegas are problems of rerouting, persistent congestion, and discrepancy in flow rate tied with starting times and link bandwidth. We reinvestigate these issues and propose modifications to the congestion avoidance mechanism of the TCP Vegas, with the slow-start and congestion recovery algorithms of Vegas remaining untouched. Unlike the solutions proposed in the recent past to deal with some of these issues, our solution is neither dependent on any critical parameter values nor on the buffer management scheme at the routers (e.g., RED). Our experiments show that the modified TCP Vegas (Vegas-A) is able to obtain a fairer share of the network bandwidth when competing with other TCP flows. We also show that Vegas-A can tackle rerouting issues and rectify Vegas's bias against higher bandwidth flows. At the same time, our experiments prove that Vegas-A preserves the properties of Vegas that have made it a noteworthy protocol.

While it has been shown that TCP Vegas provides better performance compared to TCP Reno, studies have identified various issues associated with the protocol. We propose modifications to the congestion avoidance mechanism of the TCP Vegas to overcome these limitations. Unlike the solutions proposed in the past, our solution, named TCP Vegas-A, is neither dependent on optimising any critical parameter values nor on the buffer management scheme implemented at the routers and hence can be implemented solely at the end host. Our simulation experiments over wired as well as over geosynchronous and lower earth orbit satellite links show that TCP Vegas-A is able to overcome several of the identified problems-it can obtain a fairer share of the network bandwidth in wired and satellite scenarios, tackle rerouting issues, rectify Vegas's bias against higher bandwidth flows and prevail over fluctuating RTT conditions of a lower earth orbit satellite link. At the same time, Vegas-A is able to preserve the unique properties of Vegas that had made it a noteworthy protocol.

In a Main Memory Database (MMDB) the primary copy of the database resides in volatile main memory. This makes MMDB systems more vulnerable to failures compared to the traditional Disk Resident Databases (DRDB). A backup copy of the database is maintained in secondary storage for recovery purposes. Recovery activities like logging, checkpointing and reloading are used to restore the database to a consistent state after a system crash has occurred. In this paper, we implement a recovery

Frequent Itemset Mining (FIM) is a critical data mining operation, but the computational overhead increases in the presence of large data sets and deteriorates the efficiency of FIM computation. In this paper, we explore algorithms based on CPU, GPU, and FPGA to take advantage of the parallelism in FIM computation. However, because of data transfer and memory overhead, these methods can bring negative performance. It is crucial to select the best algorithm for the particular hardware. We analyze five different methods to tackle these problems. GMiner [1] modifies Apriori algorithm [2] to minimize the memory requirements while using GPUs. To deal with exa-scale data mining operations, SGMiner [3] uses a combination of GPU and SSD to counter the memory requirements. GFPG-LLMA [4] modifies the FP-Growth algorithm [5] to make it more suitable for use on a GPU by addressing attributes of the algorithm that make it memory latency intensive. GSS [6] focuses on reducing interblock communication within GPU. The FPGA-based approaches such as Compact Architecture and Extended Architecture [7] are modifications over Eclat algorithm [8], focusing on optimizing resource utilization and speedup respectively. We observe that there is a trade-off between speedup, memory requirement, and complexity thus it is important to choose the hardware and algorithm based on the use case.

Flash memory has characteristics of out-of-place update and asymmetric I/O latencies for read, write, and erase operations. Thus, the buffering policy for flash-based databases has to consider those properties to improve the overall performance. This article introduces a new approach to buffer management for flash-based databases, called AD-LRU (Adaptive Double LRU), which focuses on improving the overall runtime efficiency by reducing the number of write/erase operations and by retaining a high buffer hit ratio. We conduct trace-driven experiments both in a simulation environment and in a real DBMS, using a real OLTP trace and four kinds of synthetic traces: random, read-most, write-most, and Zipf. We make detailed comparisons between our algorithm and the best-known competitor methods. The experimental results show that AD-LRU is superior to its competitors in most cases.

Flash memory has characteristics of out-of-place update and asymmetric I/O latencies for read, write, and erase operations. Thus, the buffering policy for flash-based databases has to consider those properties to improve the overall performance. This article introduces a new approach to buffer management for flash-based databases, called AD-LRU (Adaptive Double LRU), which focuses on improving the overall runtime efficiency by reducing the number of write/erase operations and by retaining a high buffer hit ratio. We conduct trace-driven experiments both in a simulation environment and in a real DBMS, using a real OLTP trace and four kinds of synthetic traces: random, read-most, write-most, and Zipf. We make detailed comparisons between our algorithm and the best-known competitor methods. The experimental results show that AD-LRU is superior to its competitors in most cases.

Flash memory has characteristics of out-of-place update and asymmetric I/O latencies for read, write, and erase operations. Thus, the buffering policy for flash-based databases has to consider those properties to improve the overall performance. This article introduces a new approach to buffer management for flash-based databases, called AD-LRU (Adaptive Double LRU), which focuses on improving the overall runtime efficiency by reducing the number of write/erase operations and by retaining a high buffer hit ratio. We conduct trace-driven experiments both in a simulation environment and in a real DBMS, using a real OLTP trace and four kinds of synthetic traces: random, read-most, write-most, and Zipf. We make detailed comparisons between our algorithm and the best-known competitor methods. The experimental results show that AD-LRU is superior to its competitors in most cases.

Covert timing channels in real-time systems allow adversaries to not only exfiltrate application secrets but also to mount timing inference based attacks. Much effort has been put into improving real-time system predictability with the additional benefit of reducing the former class of confidentiality attacks. However, the more predictable the system behaves, the easier timing inference based attacks become. Time-triggered scheduling is particularly vulnerable to these types of attacks due to offline constructed tables that are scheduled with clock synchronization and OS-timer predictability. In this paper, we obfuscate timetriggered scheduling to complicate timing inference based attacks while maintaining strong protection against exfiltration attacks.

Abstract: We study the buffering requirements for zero cell loss for TCP/IP over satellite links using the available bit rate (ABR) and unspecified bit rate (UBR) services of asynchronous transfer mode (ATM) networks. For the ABR service, we explore the effect of feedback delay (a factor which depends upon the position of the bottleneck), the switch scheme used, and background variable bit rate (VBR) traffic. It is shown that the buffer requirement for TCP over ABR is independent of the number of TCP sources, but depends on the aforementioned ...

Real time audio transmission over the internet has become increasingly popular in many application areas, in particular in the commercial and entertainment sectors. However, the most challenging problem of end-to-end delay over an IP network needs to be addressed and is a topic of current ongoing research. In this paper various issues related to streaming real time audio in an IP network including the protocols used, problems faced in transmission and reception have been reviewed. A new scheme to evaluate the effect of buffer size during reception of an audio transmission in order to achieve an optimized playback is developed and tested. This method can be used to optimize the reception quality with respect to time and provide a way to reduce the noise effects at the receiver. It helps to stress out the factors affecting audio playback performance for the consumer.

Complex objects to support non-standard database applications require the use of substantial computing resources because their powerful operations must be performed and maintained in an interactive environment. Since the exploitation of parallelism within such operations seems to be promising, we investigate the principal approaches for processing a query on complex objects (molecules) in parallel. A number of arguments favor methods based on inter-molecule parallelism as against intra-molecule parallelism. Retrieval of molecules may be optimized by multiple storage structures and access paths. Hence, maintenance of such storage redundancy seems to be another good application area to explore the use of parallelism.

New database applications, primarily in the areas of engineering and knowledge-based systems, refer to complex objects (e.g. representation of a CAD workpiece or a VLSI chip) while performing their tasks. Retrieval, maintenance, and integrity checking of such complex objects consume substantial computing resources which were traditionally used by conventional database management systems in a sequential manner. Rigid performance goals dictated by interactive use and design environments imply new approaches to master the functionality of complex objects under satisfactory time restrictions. Because of the object granularity, the set orientation of the database interface, and the complicated algorithms for object handling, the exploitation of parallelism within such operations seems to be promising. Our main goal is the investigation and evaluation of different hardware architectures and their suitability to efficiently cope with workloads generated by database operations on complex objects. Apparently, employing just a number of processors is not a panacea for our database problem. The sheer horse power of machines does not help very much when data synchronization and event serialization requirements play a major role during object handling. What are the critical hardware architecture properties? How can the existing MIPS be best utilized for the data management functions when processing complex objects? To answer these questions and related issues, we discuss different kinds of architectures combining multiple processors: loosely-, tightly-, and closely-coupled. Furthermore, we consider parallelism at different levels of abstraction: the distribution of (sub-)queries or the decomposition of such queries and their concurrent evaluation at an inter-or intra-object level. Finally, we give some thoughts as to the problems of load control and transaction management.

Support for temporal data continues to be a requirement posed by many applications. We show that a complex object data model is an appropriate means for handling temporal data. Firstly, we describe the main features of temporal databases in terms of time sequences, valid time, etc. We then explain the mapping of time sequences onto recursively structured complex objects. Operations on temporal data are easily transformed into complex object operations. To cope with the huge storage requirements arising from temporal databases, we integrate the concept of storing logical differences into our approach. Here, we exploit the extensibility of the underlying complex object's database system PRIMA. Finally, we briefly sketch a further improvement to guarantee fast access to the present data by storing them apart from the historical data without loosing the connection between both.

❑ Propagation delay: 24 ms❑ Avg packetization delays: 6 ms+ 6 ms (PCM)❑ Assuming 5 switches on a typical path, delay variation allowed at each switch=(100-24-6-6)/5= 12.8 ms❑ For single switch bottleneck case, End-to-end delay= 12.8+ 24= 36.8 ms≈ 40 ms❑ We tried end-to-end delay bounds of 40 ms and 30 ms.

Voice in its inherent nature is variable. It is natural to use the VBR class for voice, and transmit voice in its bursty form. On an average, human voice has an speech activity factor of about 42%. This allows us to multiplex a lot of voice sources together. We study the degradation in voice quality under various scheduling policies for VBR voice. Our simulations showed that it is desirable to keep the total VBR-voice load to about 50 % of the total link capacity, in order to maintain good quality voice. The remaining link capacity could then be filled up by data. Source:

Background: Sorghum is an important source of fodder in the semi-arid areas of Kenya. However, its biomass yield has remained low due to the low soil moisture content which is associated with low rainfall. Objective: To evaluate the synergistic effects of combining rainwater harvesting practices on biomass yield and the morphometric traits of sorghum in semi-arid Kitui County. Methodology: The study was conducted in a randomized complete block design under rainfed conditions between March and August 2021 at the Research Farm of South Eastern Kenya University. It had twelve treatments, including three farming systems (conventional flat planting, ridge and furrow, and zai pits) with three soil mulching types (transparent plastic film mulch, black plastic film mulch, and grass mulch). The farming systems without mulching were used as control treatments. Data were subjected to analysis of variance and means were separated using Fisher’s protected Least Significant Difference test at 0.05 %. Results: The zai pits with black plastic film mulch and flat planting with grass mulch had the highest and lowest moisture content of 68.65% and 52.5% respectively compared to flat planting. The highest biomass yield was observed in ridge-furrow with black plastic film mulch (3283.33kg ha-1) and ridge–furrow with transparent plastic film mulch (3266.03) and was not significantly different. The lowest biomass yield was recorded in conventional flat planting and zai pits and was not significantly different. In all treatments, there was a significant increase (p ≤ 0.05) in morphometric traits. Implications: The farming system and the type of soil mulching determined the increase of soil moisture content, biomass yield, and morphometric traits. Conclusion: Combining ridge-furrow and black plastic mulch is recommended to improve the biomass yield of sorghum in semi-arid Kitui County, and other areas with similar agroecological conditions.
Key words: Drylands; cereals; water stress; climate change.

The objective of extensible DBMSs is to ease the construction of specialized DBMSs for nontraditional applications. Although much work has been done in providing various levels of extensibility (e.g., extensibility of data types and operators, query language extensibility, and query optimizer extensibility), there has been very limited research in providing extensibility at the buffer management level. Supporting extensibility at the buffer management level is important as it can contribute significantly to overall system performance. This paper addresses the problem of supporting extensibility of buffer replacement policies. The main contribution is the proposal of a framework for modeling buffer replacement policies. This work is novel in two aspects. First, by providing a uniform and generic specification of buffer replacement policies, the proposed framework unifies existing work in this area. Second, our work introduces a new level of extensibility. None of the existing extensible DBMSs, to our knowledge, provides extensibility at the buffer management level. The proposed framework provides a basis for the construction of an extensible buffer manager as part of a 100% Java-based storage manager. We conducted an extensive performance study to investigate the performance of the proposed framework. The experimental results demonstrate that the proposed framework is indeed feasible for existing DBMSs and improves system performance significantly without costing significant overhead.

In this paper, we propose a novel external-memory algorithm to support view-dependent simplification for datasets much larger than main memory. In the preprocessing phase, we use a new spanned sub-meshes simplification technique to build view-dependence trees I/O-efficiently, which preserves the correct edge collapsing order and thus assures the run-time image quality. We further process the resulting view-dependence trees to build the meta-node trees, which can facilitate the run-time level-of-detail rendering and is kept in disk. During run-time navigation, we keep in main memory only the portions of the meta-node trees that are necessary to render the current level of details, plus some prefetched portions that are likely to be needed in the near future. The prefetching prediction takes advantage of the nature of the run-time traversal of the meta-node trees, and is both simple and accurate. We also employ the implicit dependencies for preventing incorrect foldovers, as well as main-memory buffer management and parallel processes scheme to separate the disk accesses from the navigation operations, all in an integrated manner. The experiments show that our approach scales well with respect to the main memory size available, with encouraging preprocessing and run-time rendering speeds and without sacrificing the image quality.

Recently, several external memory techniques have been developed for a wide variety of graphics and visualization problems, including surface simplification, volume rendering, isosurface generation, ray tracing, surface reconstruction, and so on. This work has had significant impact given that in recent years there has been a rapid increase in the raw size of datasets. Several technological trends are contributing to this, such as the development of high-resolution 3D scanners, and the need to visualize ASCI-size (Accelerated Strategic Computing Initiative) datasets. Another important push for this kind of technology is the growing speed gap between main memory and caches, which penalizes algorithms that do not optimize for coherence of access. Because of these reasons, much research in computer graphics focuses on developing out-of-core (and often cache-friendly) techniques. This paper surveys fundamental issues, current problems, and unresolved questions, and aims to provide graphics researchers and professionals with an effective knowledge of current techniques, as well as the foundation to develop novel techniques on their own.

The performance of the proposed algorithm, FSAMAC, is compared with the TDFQ scheme. The simulation results are presented in the following section 6.5 EXPERIMENTAL RESULTS 6.5.1 Based on No. Of Flows In the experiment the numbers of flows are varied as 2,4,6,8 and 10.

Effective buffering of optical packets is essential to the efficient working of optical packet switches. In this paper three new schemes, which involve sorting and finding the least occupied buffer, are proposed. Their performance is compared with the common round-robin scheme. The results show that all these new schemes are able to enhance the optical packet switch performance significantly in terms of packet drop/loss probability. In addition, the results show that not all the newly arrived packets need to be sorted in order to obtain the minimum packet drop probability. As computation/processing time is significant in optical packet switching, partial sorting of the newly arrived packets with tolerable packet drop probability appears to be a viable proposition. Conversely, a complete sort of newly arrived packets wastes packet processing time unnecessarily while significantly increasing the packet drop probability.

En 3G UMTS, deux canaux principaux de transport ont été crées pour la transmission de données sur le lien descendant : un canal commun FACH et un canal dédié DCH. Le performance de TCP en UMTS dépend beaucoup de la politique de commutation de canal utilisée. Dans cet article, nous proposons et analysons trois nouvelles politiques de commutations de canal pour l'UMTS basées sur des seuils simples que nous appelons politique QS (Queue Size), FS (Flow Size) et QSFS (QS et FS combinés). Ces politiques améliorent de manière significative (environ 17%) le temps de réponse par rapport à la politique modifiée de seuil de . De plus, nous proposons et évaluons une nouvelle politique de commutation, plus performante, que nous appelons politique de FS-DCH (atleast flow-size threshold on DCH). Cette politique favorise les connexions TCP courtes (i.e., de peu de paquets) et est ainsi une politique inter-couche qui améliore le performance de TCP en donnant priorité aux premiers paquets des connexions sur le canal rapide DCH. De nombreux résultats de simulation illustrent ce gain de performance dans le cas d'un petit nombre de connexions TCP.

The long term impact of contour trenching tends to be that more runoff turns into groundwater recharge. In 2008, the contribution of recharge at a contour trench plot was determined as potential and not quite visible. Recharge has not been confirmed, since groundwater level data at the contour trench plot were not available. For further study, 4 new observation wells