**3.1 Overview of Grid services**

The WLCG middleware is a complex suite of packages which includes (see also Figure 10):

Fig. 9. Grid Layers

• Information Services: **–** Accounting Service **–** Site Availability Monitor

**–** Service VO Agent Service

**–** Application Software Install Service

packages produced by other projects including, e.g.:

ARC, gLite, UNICORE and dCache

**–** Monitoring tools: experiment dashboards; site monitoring

The WLCG middleware has been built and further developed using and developing some

Grid Computing in High Energy Physics Experiments 191

• EMI (European Middleware Initiative) [26], combining the key middleware providers of

	- **–** Storage Element
	- **–** File Catalogue Service
	- **–** Grid file access tools
	- **–** File Transfer Service
	- **–** GridFTP service
	- **–** Database and DB Replication Services
	- **–** POOL Object Persistency Service
	- **–** Certificate Management Service
	- **–** Virtual Organization [25] Management Registration Service (VOMRS)
	- **–** Authentication and Authorization Service (the X509 infrastructure)
	- **–** Compute Element
	- **–** Workload Management

10 Will-be-set-by-IN-TECH

Currently, whether the data taking is going on or not, the network, especially the OPN, and the sites are under continuous checking: there are automatically generated test jobs periodically sent over the infrastructure to test the availability and functioning of the network and on-site

The WLCG integrates and operates resources distributed all over the world and its task is to make all these resources accessible and usable for the LHC experiments to distribute, archive and process the data produced by the LHC. This task is done using a specialized software called "middleware" because it sits between the operating systems of the computers at the WLCG sites and the Physics applications software used for the reconstruction, analysis and simulation of the LHC data (or any other application software layer). The middleware is a collection of protocols, agents and programs/services which we describe in the following

As we already mentioned, the Worldwide LHC Computing Grid is a distributed computing infrastructure that spans over five continents managing resources distributed across the world (due to funding, operability and access reasons). The resources operated by the WLCG belong either to the two main global grids, EGI [16] and OSG [17], or to other collaborating regional or national grids. To make this diverse variety of resources globally available for all the WLCG users, the WLCG has been developing its own middleware, a software layer that "brings all the resources together": a collection of programs, services and protocols to manage and

The WLCG middleware is a complex suite of packages which includes (see also Figure 10):

**–** Virtual Organization [25] Management Registration Service (VOMRS) **–** Authentication and Authorization Service (the X509 infrastructure)

operate the entire WLCG infrastructure (see Figure 9).

**–** Database and DB Replication Services **–** POOL Object Persistency Service

**–** Certificate Management Service

**3.1 Overview of Grid services**

• Data Management Services: **–** Storage Element **–** File Catalogue Service **–** Grid file access tools **–** File Transfer Service **–** GridFTP service

• Security Services:

• Job Management Services: **–** Compute Element **–** Workload Management

services.

section.

**3. Middleware**

**2.5 Concluding remarks**
