d, but is not very helpful when it comes to specifying distributed applications. TMN has been upgraded today and is no longer restricted to rely on the OSI upper layer architecture alone. TMN has incorporated SNMP and CORBA connec- tivity structures as realizations of mpCP network interfaces as well (see ITU-T Q.811 and Q.812). Since SNMP runs in the very network it manages (an IP network), it relies sim- ply on an TCP/UDP/IP stratum. The nodes of the SNMP management system run on TCP/UDP port number 161. SNMP does not make any distinction between actors and agents, SO there is nothing similar to CMIS/CMIP in SNMP (which partly explains its popularity over TMN). Thus, an SNMP element is a single layer element that includes an element state machine (ESM) of either the AF or OSF type, that handles SNMP-MOs. The CORBA platform, being a general platform for communication between dis- tributed objects, is designed to be possible to run on different types of connectivity strata. The connectivity structure for an mpCP realized in CORBA is therefore somewhat more complex then for SNMP (see Fig. 5.8). AF-CORBA CORBA SAGGIOP object CORBA Standardized Other Other layer interface adapt. adapt. Other TCP/UDP TCP/UDP Other strata strata Fig. 5.8 Realizing the mpCP by a CORBA connectivity structure The structure is well-aligned with the AMLn view: The CORBA layer is sepa- rated into an agent layer defined as GIOP ("general inter-ORB protocol"), where CORBA applications 6 are connected over GIOP-SAGs. The GIOP layer includes all the functions that in OSI/TMN are associated to ACSE, ROSE and CMIS/ A CORBA application consists of user defined objects and a number of CORBA defined objects and services that are available to all user defined objects. For example, user defined objects do not know in which CORBA system they exist (in this case either in an AF or in an OSF). The CORBA platform (including GIOP and IIOP) makes object distribution transparent to user defined objects. 5.3 The Management Plane Control Point (mpCP) CMIP. Alth