When a user accesses and makes use of the Grid, (s)he will be making use of a large number of separate applications running on various servers located at several different sites. Each individual application must be running correctly as must the interfaces between each application in order for the user's particular operation to be completed successfully. Additionally, in a typical user operation, only a small subset of all the applications running on the grid will need to be used.
Thus, from an end user's viewpoint, simply monitoring and reporting the status of each individual grid application in some cases provides too little information on whether the system as a whole is working, and in some cases too much information.
Service level monitoring provides a view of the system as a whole and measures whether (and how) it is providing service to end users. For the monitoring being displayed in these web pages, this is done simply by emulating an end user's typical operation (queue matching, job submission, write to local SE, job output collection).