The SAP .Net Connector processes a call from a .Net application, converts it into the RFC format and sends it via the RFC protocol to an SAP system (and vice versa). The SAP .Net Connector also retrieves the required metadata from the SAP system. The connector uses the SAP .Net Class Library to map .Net data and RFC data.
SAP.Net Connector: Architecture - Overview
SAP.Net Connector: Runtime Architecture