Grid Basics - Grid and Cloud Computing - page 22

The main functionality of each layer can be summarized as follows (Foster and
Kesselman 2004):
• The Fabric layer comprises the physical resources which are shared within the
Grid. According to Foster and Kesselman (2004), this includes computational
resources, storage systems, network resources, catalogues, software modules,
sensors and other system resources.
• The Connectivity layer “ contains the core communication and authentica-
tion protocols required for a Grid-specific network transaction ” (Foster and
Kesselman 2004). Communication protocols enable the exchange of data
between the resources of the fabric layer. The most important functionalities at
the connectivity layer include: transport, routing and naming as well as support
for a secure communication. According to Foster and Kesselman (2004), the
most important requirements for security support involve: support for single
sign on, support for delegation so that a program can run and access resources to
which the user has access, support for interoperability with local security solu-
tions and rules.
• The Resource layer uses the communication and security protocols (defined
by the connectivity layer) to control secure negotiation, initiation, monitoring,
accounting, and payment for the sharing of functions of individual resources. It
comprises mainly information and management protocols. Information proto-
cols are used to obtain information about the structure and state of available
resources. Management protocols are used to negotiate access to resources and
serve as a “policy application point” by ensuring that the usage of the resources
is consistent with the policy under which the resource is to be shared.
• The Collective layer is responsible for all global resource management and for
interaction with collections of resources (Foster and Kesselman 2004). Collective
layer protocols implement a wide variety of sharing behaviours. The most impor-
tant functionalities of this layer are: directory services, coallocation, scheduling
and brokering services, monitoring and diagnostics services and data replication
services. The services of the collective layer are usually invoked by program-
ming models and tools: Grid-enabled programming systems, workflow systems,
software discovery services and collaboration services. This layer also addresses
community authorization together with accounting and payment services.
• The Application layer involves the user applications that are deployed on the
Grid. It is important to note that not any user application can be deployed on
a Grid. Only a Grid-enabled or gridified application, i.e. an application that is
designed or adjusted to run in parallel and use multiple processors of a Grid
setting or that can be executed on different heterogeneous machines (Berstis
2002), can take advantage of a Grid infrastructure.
The five layers of Grid Computing are interrelated and depend on each other. Each
subsequent layer uses the interfaces of the underlying layer. Together they create the
Grid middleware and provide a comprehensive set of functionalities necessary for
enabling secure, reliable and efficient sharing of resources (computers, data) among
independent entities. This functionality includes low-level services such as security,