External Sourcing for Purchase Requisitions 
In order to generate follow-on documents for purchase requisitions created in the SAP ERP system, you must assign a valid source of supply. If there are no valid sources of supply in SAP ERP, the purchaser can carry out external sourcing using the SAP SRM system.
There are two processing modes available for transferring purchase requisitions to the SAP SRM system:
Background mode
Purchase requisitions are transferred to SAP SRM automatically, and are created as external requirement documents in the SAP SRM system. Subsequently, the purchaser can process and convert the external requirement document into a follow-on document (for example, a purchase order, contract, RFx or auction) directly in the SAP SRM sourcing application.
Online mode
Purchasers transfer purchase requisitions manually using the Collaborative Processing of Purchase Requisition (CPPR) application. In online mode, purchasers can choose to either transfer purchase requisitions to SAP SRM by creating an external requirement document in SAP SRM, as in background mode, or create an RFx for the purchase requisition directly in SAP SRM. If the purchaser chooses to create an RFx directly in SAP SRM, no external requirement is generated for the purchase requisition.
Note
Before you configure this process, you must first configure the basic settings for the Plan-Driven Procurement with Plant Maintenance business scenario. You do this in SAP Solution Manager under .
The following business process runs in SAP SRM:
Start Collaborative Processing of Purchase Requisitions (CPPR) application
Create RFx from CPPR
Transfer purchase requisition to SAP SRM sourcing application