Service Users for Internal Communication 
These service users are used for internal communication between PI components, which is usually triggered by the interaction of dialog users. The service user provide dialog-free access to the involved PI components.
For an overview of the internal communication within a PI landscape (Advanced Adapter Engine Extended), see Communication.
The following general principles apply for internal communication:
Each PI component that communicates with other PI components identifies itself by means of a dedicated service user. Therefore, each required service user must be created in each target component.
This service user has all the necessary authorizations to access the required services on the addressed PI components.
Example
The Enterprise Services Repository is associated with service user PIREP<SID> (where <SID> is the system ID). Since the Enterprise Services Repository needs to communicate with the Integration Directory (for the cache refresh mechanism) and the System Landscape Directory (to obtain physical channel data), the user PIREP<SID> needs to be known by each of these components.
For each component, service user representing the respective components are created with the appropriate roles in the target components during basic configuration. The passwords of the service user have to be defined during the basic configuration process.