I DONEIDAD DE LAS PRUEBAS

To be able to implement services, the research tried to study the facilities that have been used in literature. This subsection will concentrate on facilities required to build MODO services within grid environment. To build a reliable grid system, certain facilities are required. Major grid facilities for implementing grid services are

discussed below so that during design and implementation of DECGrid in chapters 5, 6 and 7, it will be easy to identify the components to be used.

2.9.1 Middleware

One of the main components of grid infrastructure is the middleware. Middleware is the software and hardware systems that enable interoperability among different platforms and users of the grid from distributed locations (Foster and Kesselman, 1999). For example, different users use different operating systems, communication protocols, databases, software, hardware, certificate authorities (CAs) and schedulers. For these different grid components to ‘talk’ to each other effectively, good middleware services are required. Globus Toolkit is one of the most popular grid middleware. MODO services need robust middleware to provide collaborative environment for professionals using different platforms.

2.9.2 Portals

Portals are the access points to grid resources. One of the efficient qualities of a grid service is the single sign-on method that allows a user to have access to any resource. Portals have GRAM (Grid Resource Allocation Management) job manager and gatekeeper that authenticate and authorise users before allowing them to have access to the grid. The proposed DECGrid uses portal for users to have access to resources that they have rights to access. This solves the problem of multiple authentication and access. However, this feature is sometimes criticised by industrial grid users (Surridge and Taylor, 2005). Companies do not want third parties to give access to other users on their behalf. They want to have autonomy over the rights to share data and information. This might be for competitive business issues.

2.9.3 Certificate authority

Trust and security is the key to a successful grid deployment that provides MODO services (Foster et al., 1998b). Managing cross-boundary trust among many users using different grid certificates requires the involvement of the certificate authorities. A certificate authority (CA) is a body or organisation that issues certificate for grid users. Examples of CAs are Globus and Science and Technology Facilities in the US and UK respectively. A certificate is the public key (encrypted) and information about its owner linked to the CA digital signature. Every resource, service or user has a certificate. A computing resource has a host certificate (hostcert) and host key

(hostkey). A user has a user certificate (usercert) and user key (userkey) and resource or service has resource certificate/key or service certificate/key. This pair (certificate and key) is called host credentials for computers, user credentials for users, resource credentials for resources and service credentials for services. There are public and private credentials. Proxy credentials are short-lived credentials. A user is identified by the certificate subject in the grid map file. A grid map file maps certificate subjects to local usernames. A CA signing policy is used to place strict compliance to the information one gives to a CA to bind to a key. There are different CA models. VOs find it difficult to manage different CAs and may soon adopt a common CA model (Johnston, 2003). The Globus Toolkit GSI uses Secured Shell (GSSH) for authenticating resources and services that need to be transferred from a distant site of a grid. CA defines both global and local authorisation and authentication of users and services to ensure a trustworthy grid infrastructure.

2.9.4 Schedulers

Schedulers ensure optimum utilisation of grid resources and services. Conventional scheduling systems such as Portable Batch Scheduling (PBS) and Sun Grid Engine (SGE) are used in conjunction with Globus GRAM to perform resource scheduling within VO. Condor is a dynamic scheduling software for the grid which works with GRAM to perform cycle stealing. Condor-G, as it is called, improves computing throughput by utilising the idle cycles of a company’s desktops when users are not using their systems. This has the economic advantage of reducing the amount of money and resources spent on supercomputers (Abbas, 2001). Different grid users have different requirements and priorities. Schedulers ensure that these different users are satisfied through appropriate allocation of resources to them.

2.9.5 Resource brokers

Resource brokers receive request from users and sends these to GIS. A GIS search for the resources or services requested for and sends feedback to users through resource brokers. Resource brokers are the negotiating ‘middle-men’ between grid resources and users. Nimrod-G and Gridbus are good examples of resource brokers (Buyya, 2002). Resource brokering is an integral part of the grid infrastructure. It ensures feedback loop to users on whether or not a resource or service is available. This feature plays a role in ensuring QoS to users.

2.9.6 Operating systems

Operating systems (OS) such as Linux, Mac OS, Sun Solaris, UNIX, MS Compute Cluster Server and Windows OS play major roles in grid deployments. Linux happens to be the most widely used OS among grid users. This is because of the open source philosophy of Linux, and grid infrastructures are based on open source standards. Linux, UNIX and some operating systems already have in-built security and file transfer protocols that enable large-scale computing. For example, transferring large files from one machine to another machine at a distance using the command ‘scp <source file> <destination file>’ in Linux provides encryption for the file on transit until it reaches its destination. This complements the Globus GSI. In addition, OS ensures stability and reliability of grid systems. Some OSs have Multiple Processing Interface (MPI) built in them. This makes parallel scheduling easy as users can choose which processor they want to send their jobs to rather than just a random allocation of jobs to processors. OSs occupy low-level resource layer in the grid architecture, signifying their importance as resources for communication among different grid users from geographically separated sites (Foster and Kesselman, 1999).

2.10 Gaps in literature

From Figure 2.2, the research shows that most grid optimisation research uses the grid for computational and data intensive purposes. This is basically to speed up computation or simulation of data. Literature does not report the requirements from grid environment for MODO. Though projects such as the Geodise and DAME used grid for optimisation, there is an absence of high-level grid service specification document for designers to support MODO. This document should include features that bind service providers and end users. The document usually seen is the use case diagram and class diagram for programmers to develop the services. There is a need to include at the beginning of the service specification a service level agreement between providers and end users. This will ensure that grid services comply with some level of quality of services provided.

Another research gap is the lack of precise process for providing services. This includes steps such as identification of service users, identification of type of suitable grid services for the users, definition of service requirements for the users and identification of the need for service level agreement and service implementation. By

providing such steps, it will be clear as to which type of grid services are suitable for a particular application. Again, the service specifications found in literature are mainly for the use of programmers and not for other users of the system. This research provides service specifications for MODO so that it can be used and referenced by both programmers and users. The design of the service and schema for quantitative and qualitative mathematical model building in the MODO is another gap in literature. The proposed interface provides an easy interface for designers when carrying out optimisation.

Literature highlights the need to develop a grid architecture to support the MODO service. Grids are meant for large-scale distributed applications. Initial grid implementation issues for scalability and collaboration are most of the time neglected. A campus grid could eventually grow into a national grid and so there is the need to put in place measures that will take care of such issues. This research provides a step by step road map to tackle this issue. The steps are shown as the process that a service provider needs to follow at the initial stage of creating MODO services.

2.11 Summary

This chapter reviews literature in grid computing, grid projects, MODO methods and problem solving environments. Web and grid service protocols, middleware and scheduling systems were also reviewed. Gaps in literature were identified. The next chapter will use these findings to provide the aim, objectives, research questions and methodology for the research.

Chapter 3 - Research Aim, Objectives and