The Operations System Functions (OSF) block initiates management operations and receives notifications. In terms of the manager-agent model, the OSF may be seen as the manager specific functions. An OSF communicates with the NEF over a q 3 reference point (Figure 7).
The initial 1988 version of M.30 defined three different q reference points: q 1 , q 2 and q 3 . The q 3 reference point is used whenever management information should be exchanged via an application layer management protocol, such as the Common Management Information Protocol (CMIP ) of OSI. The two other reference points were intended for cases in which management information should be exchanged via lower layer (e.g. data link) management protocols. After some time it appeared however that it was impossible to make a distinction between q 1 and q 2 ; these two reference points were therefore replaced by the generic q x reference point.
Figure 8 shows the relation between OSF, NEF and q 3 , expressed in terms of the OSI service and protocol concepts. The service provided at the q 3 reference point is generally the Common Management Information Service (CMIS ).
Within a single TMN (operated by a single administration) multiple OSFs may be defined. If necessary, these OSFs can communicate with each other over q 3 reference points. It is also possible that OSFs in different TMNs (operated by different administrations) communicate with each other; in this case communication takes place over a x reference points.