27275974
Distributed Spatial Catalog Service on the CORBA Object Bus
Spatial catalog service is a necessary component for distributed geographic information. Spatial catalog services provide the capabilities for organizing and managing spatial metadata. Catalog services simplify the process of data discovery in a large spatial database, facilitate data transfer, and help data fusion.This paper presents a software architecture for spatial catalog services. We first discuss the general concept of spatial catalog facilities and the logical model of spatial catalog services. We then introduce the distributed object-oriented model for spatial catalog services based on the industrial standard Common Object Request Broker Architecture (CORBA). The core components of spatial catalog services, catalog and catalog registry, are described in detail with the CORBA Interface Definition Language (IDL). Examples are given to illustrate the structure of the catalog component and its relations with other service components in a distributed GIS. The model provides a common interface to spatial catalogs and related data no matter how catalogs are defined, what formats they use, and where they are located. It provides crucial services in a distributed Geographic Information System.
2212152
A Model of GIS Virtual Machine
Abstract This paper presents a model of Geographic Information System Virtual Machine. The GIS VM is a software architectural model that facilitates the development of Web-based GIS applications. It is a three-tiered system. Java applets or ActiveX objects, with Web browsers as the container, form the presentation tier that interacts with the user. The core of the GIS VM is the servers in the middle and third tiers. The middle tier includes server components for basic GIS functions and data discovery. The third tire mainly contains the spatial data access server. In addition to these basic servers, the GIS VM includes a model object manager (MOM) that establishes linkages with external models and other application programs. The MOM can also extract metadata about models and carry out the execution process on a user's behalf.
28617398
An Unbalanced Multiple Description Coding Scheme for Video Transmission Over Wireless Ad Hoc Networks
29218953
On Handoff Performance for an Integrated Voice/Data Cellular System
One of the key challenges in the design of bandwidth allocation policies for a multi-services mobile cellular network is to guarantee the potentially different Quality of Service (QoS) requirement from diverse applications, while at the same to ensure that the scarce bandwidth be utilized efficiently. Complete Sharing (CS) and Dynamic Partition (DP) schemes have been shown as viable techniques for managing the bandwidth. However, there has been no study that compares their respective performance, which is the focus of this paper. Specifically, in this paper, through both analysis and simulation, we demonstrate that both schemes can achieve comparable performance by proper manipulation of control parameters. The tradeoff is that DP scheme can more easily achieve the target QoS requirement, at the expense of some over-provisioning, thus can potentially lead to less channel efficiency when comparing to a CS based scheme.
5860763
Theoretical analysis of transmission characteristics for all fiber, multi-cavity Fabry-Perot filters based on fiber Bragg gratings
The characteristics of transmission spectra for the all fiber, multi-cavity Fabry-Perot (FP) configuration based on fiber Bragg gratings (FBG) are theoretically analyzed and modeled. The general transmission matrix function for the structure with any number of cavities is derived, and explicit expression of the power transmission coefficient for symmetrical two-cavity FP is presented. The general conditions for flat-top single resonant peak at the central wavelength in FBG stop band are derived and verified in the numerical simulation section. The transmission peaks of single-cavity and two-cavity FP structures are compared and discussed, and results show that compared to the single-cavity FP, flatness of the top and steepness at the edge of transmission peak can be improved by introducing one more cavity. The resonant transmission peak properties of two-cavity structure are investigated in detail for various values of cavity length and FBGs with different reflection characteristics, and the design guidelines for transmission-type filters are presented. The results show that the steepness of peak slope can be improved by increase of FBG reflectivities, and these kinds of filters can be used as narrow-band single-channel selectors and multi-channel wavelength de-multiplexing by properly choosing the length of cavities and reflectivities of FBGs.
1252893
A Configurable Web Service Performance Testing Framework
More and more softwares based on web service technologies are developed. Before their releases on the Internet, it is necessary to evaluate these systems' performance, especially their response time under different workload pressures. However, existing performance testing benchmarks and tools for web service applications are difficult to adapt to various user-specific testing purposes. This paper proposes a configurable web service performance testing framework which contains client module, application server module and database module. Client module, by using the network cooperation method that one central client drives several other clients, adapts to a great number of concurrent customers to request web services. Application server module contains web services under testing and external supporting web services, each of which is configured as a plug-in. The process to realize mixed ratio of web service interactions is similar to dealing cards and adapts to different commercial application characteristics. In database module, the data model including table and attribute dependence can be customized, and the data scale initialization can be resized according to the topology of above dependence. As such, this framework allows testers to dynamically define their data model, customize their scale of database, configure their transaction characteristics, deploy their application strategies and confirm their performance metrics..
2517026
On Dynamic and Concurrent Model of Web Service Components
The researches of Web service fasten on composition process, and are lack of the formalized description on dynamic attributes of service component itself. Aiming to these, a new dynamic and concurrent model of Web service component is presented. Firstly, this paper analyzes the process of state transition of service component under certain actions, and then depicts the dynamic transition process of service component with the state transition graph. At last, the physical representation method in memory and the algorithms to judge equivalence of state transition graph are given. Comparing with existing researches, the dynamic evolvement of service component under the actions is considered, and the algorithm to judge equivalence of service components provides an effective tool for model verification.