Known Usage
(A)LPC is used heavily in communication between internal subsystems in Windows NT. The Win32 subsystem uses (A)LPC heavily for communication between client and the subsystem server (CSRSS). Quick LPC was introduced in version 3.51 of Windows NT to make these calls faster. This method was largely abandoned in version 4.0 in favor of moving the performance critical server portions into kernel mode (win32k.sys).
The Local Security Authority Subsystem Service (LSASS), Session Manager (SMSS), and Service Control Manager all use (A)LPC ports directly to communicate with client processes. Winlogon and the Security Reference Monitor use it to communicate with the LSASS process.
As mentioned, RPC can use (A)LPC as a transport when the client and server are both on the same machine. Many services that are designed to communicate only on the local computer use (A)LPC as the only transport through RPC. The implementation of remote OLE and DCOM in many cases uses (A)LPC for local communication as well.
Read more about this topic: Local Procedure Call
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