# 7.2.3. Flow-of-Control

Describe how allocation requests are flowed to the scheduler, scheduler attachment upon startup of either side, where response to allocation requests are returned and how they get back to the requestor, where session controls are received for allocation instantiation and how that is done, where session control is called to indicate all jobs complete in session.

Probably best to start with an overview of how things flow and then drill down into the respective steps.

Allocation requests have to be serviced by the scheduler. Since a requestor could attach directly to the scheduler (e.g., in the case of a tool submitting a session request) or to a daemon within the RM (who must then relay it to its system controller for forwarding to the scheduler), the scheduler must inform the RM of the allocation via the `PMIx_Session_control` API - i.e., the RM cannot guarantee its ability to intercept and process an allocation response to learn of a session that needs to be instantiated.

PRRTE’s role in the `PMIx_Allocation_request` flow is simply to pass the request on to the scheduler, and transport the reply back to the requestor.

PRRTE only creates a session object as a result of a call from the scheduler via `PMIx_Session_control`.