DCOM provides the most direct approach to communication, requiring no additional runtime applications on the server. 

DCOM provides the only approach that lets you use security services when writing a transactional data module. These security services are based on assigning roles to the callers of transactional objects. When using DCOM, DCOM identifies the caller to the system that calls your application server (COM+ or MTS). Therefore, it is possible to accurately determine the role of the caller. When using other protocols, however, there is a runtime executable, separate from the application server, that receives client calls. This runtime executable makes COM calls into the application server on behalf of the client. Because of this, it is impossible to assign roles to separate clients: The runtime executable is, effectively, the only client.