Towards market-oriented Clouds

In the literature, Cloud computing is seen as an evolution of Grid computing, which itself is an evolution of distributed computing and supercomputing. The distinction between the Grid and Cloud concepts is not clearly defined, both of them referring to an externalization of the private data centres. Two main advantages are expected from these two approaches. Instead of investing in the installation and management of its own computing infrastructure, an enterprise may benefit from shared computing resources managed on a remote site by a third party. This third party is known as the Grid/Cloud service provider (GSP or CSP, respectively). This means that both capital expenditures and operational expenditures of the enterprise may be considerably reduced against a moderate increase in service expenditure. In the years 1990s, Grid computing was mainly developed in the perspective to provide affordable high-performance computing to small and medium enterprises. Circa 2000, Cloud Computing has been introduced by the service sector with the objective to extend the externalization of hardware resources to software resources. This distinction added to the fact that in 20 years, not only professionals but also residential users benefit from highspeed Internet access are at the origin of the Cloud computing concept. The economical models of Grid computing and of Cloud computing are quite different. Cloud computing enables the externalization of software resources at a very large scale for residential users; whereas; Grid computing mainly refers to the provisioning of externalized large computing facilities for professionals. Today, both types of services are accessible via simple Web portals. This evolution has motivated the emergence of numerous start-ups and companies specialized in service provisioning with an expected market size by 2011 around $95 billion in business and productivity applications (email, office, CRM, etc.) according to Merrill Lynch analysts. The fields of application of Cloud computing seems almost unlimited, all the sectors of our economy being concerned. Applications are ranging from distant medical diagnostic, collaborative image processing, scientific computation, financial operations, and industrial processes to radio astronomy already financially benefiting from advantages of Clouds or Grids. Two other criteria are also to be considered to distinguish between Grid and Cloud services. The consumers of Cloud services being in majority residential users, the mode of payment of the consumers is carried out on-the-fly with a duration-based charging. The consumers of Grid services being in majority enterprises, their first requirement is rather the availability of the computing resources than the price of the service itself. Resources are in that case reserved in advance for a longer period of time than in the case of Cloud services. A last distinction may be done between Grids and Clouds. In the case of Grids, heterogeneous computing resources managed by different entities may have to interoperate to provide the required service. This is not the case in the context of Clouds where comparatively, a smaller computing power is requested for a given service. Homogeneous hardware M. Gagnaire (*) Institut Telecom/Telecom ParisTech, Paris, France e-mail: gagnaire@telecom-paristech.fr