Windows 95 Dial-Up Networking provides four built-in Session Management Modules (SMMs):
However, in some Dial-Up environments, extra steps may be required to set up the dial-up session. Windows 95 Dial-Up Networking allows a third-party developer to provide these steps in a separate Session Management Module, referred to as Session Management Module Overlay, in addition to the default or other Session Management Modules, referred to as Overlaid Session Management Modules.
An overlaying Session Management Module is implemented and installed as a stand-alone SMM Dynamic-Linked Library. (See section 3 of this document for installation details). Dial-Up Networking and users see it as an additional SMM (or Dial-Up Server type) and associate it with the connection. However, when Dial-Up Networking requests the overlaying SMM to configure and manage the session, it may choose to perform additional steps or fail the configuration before handing off the control to the overlaid SMM. Once the hand-off occurs, the overlaying SMM will no longer control the session. All the interactions will occur directly between Dial-Up Networking and the overlaid SMM.