A joint team of researchers from the Mathematics and Computer Science Division of the Argonne National Laboratory and from the University of Southern California's Information Sciences Institute is developing a basic software infrastructure for high performance computing which integrates all sorts of geographically distributed computational and information resources. The scientists, involved in the project, refer to this framework of interlinked virtual supercomputers as the Globus metacomputing toolkit. Large-scale testbeds are deployed to evaluate the performance and functionality of the various tools and to figure out how to construct applications that can exploit the distributed resources available on a computational grid. In this regard, the researchers have discovered how the modular Globus toolkit components are able to provide the indispensable low level mechanisms for the specific requirements and higher level services in a telemedical environment.
Within the Globus metacomputing toolkit, each module defines an interface and also provides an implementation. Six of these identified modules are able to offer vital services in a telemedical framework where the physician, the patient, as well as the medical equipment are typically spread over different locations. The resource location and allocation function involves the expression of application resource requirements, their identification and subsequent scheduling to start the processing or the data access. The communications mechanisms allow to use a variety of methods, including message passing, remote procedure call, multicast or distributed shared memory while taking in account factors such as latency and bandwidth. The user is supplied with real time information about the metasystem's status and structure by means of the unified resource information service.
The authentication interface regulates the security services with regard to sensitive data like electronic patient records. Applied mechanisms include validation of user and resource identity, authorization and protection of data. After resource location and allocation, process creation has to be activated to start the computational task, integrate the action into the rest of the computation and monitor termination and process shutdown. High speed remote access to extended databases or file storage resources is managed by the data access module via CORBA or the Common Object Request Broker Architecture. The Globus toolkit modules constitute the defining building blocks of one single virtual machine, which is able to perform telemedical tasks on distributed and heterogeneous collections of resources which have been unified in the supercomputing environment.
In addition, the Globus team has defined a universal access mechanism to retrieve information at each imaginable level. The metacomputing directory service (MDS) consists of a framework in which data can be represented in all kinds of distributed computing applications via the lightweight directory access protocol (LDAP). MDS allows the patient information to be stored as a hybrid data object with open as well as closed parts. Via the open part, the patient participates in the telemedical framework as a resource while via the closed part, an object identifier can track down the secure and sensitive patient information. In this configuration, each administrative domain has to be responsible for its own LDAP server. The Globus project team thus makes use of the World Wide Web to assign computations to idle compute servers or to rarely available unique compute resources.
The components of the Globus metacomputing toolkit already have been demonstrated in the Globus Ubiquitous Supercomputing Testbed, referred to as GUSTO. The extensive testing of the modules will lead the research team for the next two years at least, to further refinement of the components in order to design and build quality implementations for higher level services in various application domains. In this regard, telemedicine is lending itself perfectly to the computational framework of the Globus project. For a comprehensive report on the implementation of the Globus metacomputing toolkit in a telemedical environment, we refer to Future Generation Computer Systems, Volume 14, June 1998, Numbers 1-2, pp. 109-123. General information about the Globus concept is to be found at the Globus project Web site.