The top-level entities (and the layers to which they correspond) are:

    application                   _DNS_Clerk
                                 |_DNS_Server
                                 |_DTSS
                                 |_Event_Dispatcher
                                 |_Alias (OpenVMS)
                                 |_Loopback_Application
                                 |_X25_Client (OpenVMS)
                                 |_X25_Access
                                 |_X25_Relay (Alpha)
                                 |_X25_Server
                                 |_DSA
    session                      |_Session_Control
                                 |_OSAK
    transport                    |_NSP
                          Node---|_OSI_Transport
    network                      |_Routing
                                 |_X25_Protocol
    datalink                     |_XOT (OpenVMS Alpha)
                                 |_LAPB
                                 |_CSMA-CD
                                 |_LLC2
                                 |_MOP
                                 |_HDLC
                                 |_DDCMP (OpenVMS VAX)
                                 |_FDDI
                                 |_Modem_Connect
                                 |_Device
                                 |_Frame (OpenVMS)
                                 |_Token_Ring (Tru64 UNIX)

    Select an entity listed below for a description of that particular
    module and a listing of its subentities.  Or to quickly view the
    subentities beneath a particular module while at the NCL> prompt,
    type HELP ENTITY <module_name> SUBENTITIES.