Remote Procedure Call (RPC)
This service enables the RPC endpoint mapper to support RPC connections to the server. This service also serves as the Component Object Model (COM).
RPCs and lightweight remote procedure calls (LRPCs) are important inter-process communication mechanisms. LRPCs are local versions of RPCs. LRPCs are used between the Exchange store and those server components that depend on MAPI and related APIs for communication, such as messaging connectors to non-Exchange messaging systems. Regular RPCs, however, are used when clients must communicate with server services over the network. Typical RPC clients are MAPI clients, such as Microsoft Outlook and Exchange System Manager, but internal components of System Attendant, such as DSProxy, are also RPC clients. To accept directory requests from MAPI clients and pass them to an address book provider, DSProxy must use RPCs to communicate with Active Directory through the name service provider interface (NSPI).
It is important to understand that RPCs are an application-layer communication mechanism, which means that RPCs use other network communication mechanisms, such as NetBIOS, named pipes, or Windows Sockets, to establish the communication path. To create a connection, the RPC endpoint mapper is required, because the client must first determine the endpoint that should be used. RPC server services use dynamic connection endpoints, by default. In a TCP/IP network, the client connects to the RPC endpoint mapper through TCP port 135, queries for the current TCP port of the desired service (for example, the Name Service Provider Interface (NSPI) port of Active Directory), obtains this TCP port from the endpoint mapper, and then uses this TCP port to establish the RPC connection to the actual RPC server. The following figure illustrates the role of the RPC endpoint mapper.