12876856
Virtual cell in mobile computer communications
In this paper, we design and develop a virtual cell approach for the transmission of IP datagrams in mobile computer communications. A virtual cell consists of a group of physical cells whose base stations are implemented by remote bridges and interconnected via high-speed datagram packet-switched networks. Host mobility is supported at the data link layer by virtual cell protocol (VCP) using the distributed hierarchical location information of mobile hosts. As far as the IP layer is concerned, it appears within a virtual cell as if the communication between two mobile hosts in different physical cells were taking place directly as in the same physical cell. Between virtual cells, a one-hop forwarding pointer from a mobile host's native virtual cell to its current virtual cell is maintained at the VCP layer. This means that the combination of the existing routing protocols of the IP layer and the forwarding pointer maintained at the VCP layer between virtual cells gives the same effect of having a fully duplicated location information among virtual cells for the global mobile network. Thus, the virtual cell approach eliminates the necessity of IP-level mobile host protocols that may interfere with the conventional IP protocol in a practical sense. In addition, given mobility and communication patterns among physical cells, it achieves a logically flexible coverage area of a virtual cell so as to minimize the total communication cost for the global mobile network where inter-virtual cell communication is more expensive than intra-virtual cell communication (K. Lim and Y.-H. Lee, IEEE Personal, Indoor and Mobile Radio Communications PIMRC'94, pp. 1237-1241, Sep. 1994; K. Lim, Y.-H. Lim and Y.-H. Lee, IEEE ICC'95, pp. 1839-1843, June 1995). To demonstrate the correct operations of VCP and measure data which are used as parameters to a performance model for the virtual cell system, we implement VCP on a simulated environment. The performance analysis of the virtual cell system is out of scope in this paper and one is referred to K. Lim, Y.-H. Lim and Y.-H. Lee, Proc. 10th Int. Conf. Information Networking ICOIN-10, pp. 551-560, Jan. 1996.
10753893
Evaluation of Error Recovery Blocks Used for Cooperating Processes
Three alternatives for implementing recovery blocks (RB's) are conceivable for backward error recovery in concurrent processing. These are the asynchronous, synchronous, and the pseudorecovery point implementations. Asynchronous RB's are based on the concept of maximum autonomy in each of concurrent processes. Consequently, establishment of RB's in a process is made independently of others and unbounded rollback propagations become a serious problem. In order to completely avoid unbounded rollback propagations, it is necessary to synchronize the establishment of recovery blocks in all cooperating processes. Process autonomy is sacrificed and processes are forced to wait for commitments from others to establish a recovery line, leading to inefficiency in time utilization. As a compromise between asynchronous and synchronous RB's we propose to insert pseudorecovery points (PRP's) so that unbounded rollback propagations may be avoided while maintaining process autonomy. We developed probabilistic models for analyzing these three methods under standard assumptions in computer performance analysis, i.e., exponential distributions for related random variables. With these models we have estimated 1) the interval between two successive recovery lines for asynchronous RB's, 2) mean loss in computation power for the synchronized method, and 3) additional overhead and rollback distance in case PRP's are used.
40618061
Transaction Recovery in Distributed DB/DC Systems: A Progressive Approach
920212
Resource scheduling in dependable integrated modular avionics
In the recent development of avionics systems, integrated modular avionics (IMA) is advocated for next generation architecture that needs integration of mixed criticality real-time applications. These integrated applications meet their own timing constraints while sharing avionics computer resources. To guarantee timing constraints and dependability of each application, an IMA-based system is equipped with the schemes for spatial and temporal partitioning. We refer the model as SP-RTS (strongly partitioned real-time system), which deals with processor partitions and communication channels as its basic scheduling entities. This paper presents a partition and channel-scheduling algorithm for the SP-RTS. The basic idea of the algorithm is to use a two-level hierarchical schedule that activates partitions (or channels) following a distance-constraints guaranteed cyclic schedule and then dispatches tasks (or messages) according to a fixed priority schedule. To enhance schedulability, we devised heuristic algorithms for deadline decomposition and channel combining. The simulation results show the schedulability analysis of the two-level scheduling algorithm and the beneficial characteristics of the proposed deadline decomposition and channel combining algorithms.
31591898
Scanning the issue - special issue on real-time systems
30590203
Efficient State-Saving Architectures for Power-Mode Switching
Time and energy is expended in switching between power modes (e.g., active, hibernate, sleep, etc.). Powering off cache is one major reason for this. When there is a switch in the power-mode involving cache power-off, the system spends time and energy in filling the cache with new data (inherent cache misses). In our technique, before powering off the cache, we save its state in Embedded DRAM and bring it back when the previous power mode is restored. Our experiments have showed that in a majority of cases the cache contents are too valuable to be erased. By saving the contents we can reduce switching speed and energy. We present a heuristic to save the most relevant cache contents so that power and delay overheads are minimized. To measure the area overhead a synthesizable VHDL model was designed.
850911
Usability-based caching of query results in OLAP systems
In this paper we propose a new cache management scheme for online analytical processing (OLAP) systems based on the usability of query results in rewriting and processing other queries. For effective admission and replacement of OLAP query results, we consider the benefit of query results not only for recently issued queries but for the expected future queries of a current query. We exploit semantic relationships between successive queries in an OLAP session, which are derived from the interactive and navigational nature of OLAP query workloads, in order to classify and predict subsequent future queries. We present a method for estimating the usability of query results for the representative future queries using a probability model for them. Experimental evaluation shows that our caching scheme using the past and future usability of query results can reduce the cost of processing OLAP query workloads effectively only with a small cache size and outperforms the previous caching strategies for OLAP systems.
41948538
Enhanced Model Representations for an Intra-Ring Synchronous Optical Network Design Problem Allowing Demand Splitting
In this paper, we consider a network design problem arising in the context of deploying synchronous optical networks (SONET) using a unidirectional path switched ring architecture, a standard of transmission using optical fiber technology. Given several rings of this type, the problem is to find an assignment of nodes to possibly multiple rings, and to determine what portion of demand traffic between node pairs spanned by each ring should be allocated to that ring. The constraints require that the demand traffic between each node pair should be satisfiable given the ring capacities, and that no more than a specified maximum number of nodes should be assigned to each ring. The objective function is to minimize the total number of node-to-ring assignments, and hence, the capital investment in add-drop multiplexer equipments. We formulate the problem as a mixed-integer programming model, and propose several alternative modeling techniques designed to improve the mathematical representation of this problem. We then develop various classes of valid inequalities for the problem along with suitable separation procedures for tightening the representation of the model, and accordingly, prescribe an algorithmic approach that coordinates tailored routines with a commercial solver (CPLEX). We also propose a heuristic procedure which enhances the solvability of the problem and provides bounds within 5--13% of the optimal solution. Promising computational results are presented that exhibit the viability of the overall approach and that lend insights into various modeling and algorithmic constructs.
207563187
Data quality assessment
How good is a company's data quality? Answering this question requires usable data quality metrics. Currently, most data quality measures are developed on an ad hoc basis to solve specific problems [6, 8], and fundamental principles necessary for developing usable metrics in practice are lacking. In this article, we describe principles that can help organizations develop usable data quality metrics.
18483923
Network selection and discovery of service information in public WLAN hotspots
In a public WLAN hotspot, a roaming mobile terminal (MT) may be within radio range of more than one access point (AP), each of which may or may not have roaming agreements with the service provider of the user of the MT. In this case, the MT may need to discover some <i>service information</i> before it can make an intelligent <i>network-selection</i> decision. The most critical is <i>roaming information</i>; while other information such as <i>security policies</i>, <i>price</i>, <i>AP workload</i> may also be useful. Currently, roaming information is typically provisioned on the MTs as static <i>roaming tables</i> or <i>roaming lists</i>. However, this approach may not scale well when there are millions of hotspots globally. Addressing this shortcoming, recently several solutions have been proposed by different groups. In this paper, we contrast these solutions, and propose our own solution called <i>Roaming Information Code (RIC)</i>, which can be transported as SSID or a new Information Element of the 802.11 standard. RIC is scalable and can be fully backward compatible with existing APs (if transported as SSID). Furthermore, it does not hinder fast handoffs. In the second half of the paper, we will also discuss two other schemes addressing the other service information: a scheme called <i>RIC-VAP</i> for provider-specific security information; and a scheme that allows an AP to announce price and workload information.
12566781
Web-Based Simulation with Server Application Approach under Distributed Environment