Reference Counting
In the COM network protocol, remote reference counting is conducted on per-interface (per IPID), just as local reference counting is carried out on a per-interface basis.
The actual increment and decrement calls are carried out using (respectively) the RemAddRef and RemRelease methods in a COM interface known as IRemUnknown found on an object associated with the each OXID, the IPID of which is returned from the function IObjectExporter::GetStringBindings (see below). In contrast to their analogues in IUnknown, RemAddRef and RemRelease can in one call increment or decrement the reference count of many different IPIDs by an arbitrary amount; this allows for greater network efficiency.
In the interests of performance, client COM implementations typically do not immediately translate each local AddRef and Release into a remote RemAddRef and RemRelease. Rather, the actual remote release of all interfaces on an object is typically deferred until all local references to all interfaces on that object have been released. Further, one actual remote reference count may be used to service many local reference counts; that is, the client infrastructure may multiplex zero or more local references to an interface into zero or one remote references on the actual IPID.8.