Further remarks

Besides the function blocks and reference points, the TMN functional architecture introduces some additional concepts. These concepts are:

• TMN's Data Communication Function
• TMN's functional components

According to recommendation M.3010, "TMN's Data Communication Function (DCF) will be used by the function blocks for exchanging information. The DCF provides layers 1 to 3 of the OSI RM".

The definition of the DCF concept has historical reasons: in initial drafts of TMN the DCF was modelled as a function block; it was therefore part of TMN's functional architecture. At present the DCF is no longer modelled as a function block; the text that describes the DCF remained, however.

Each of TMN's function blocks is itself composed of a number of functional components. The following functional components are defined:

• Management Application Function.
• Management Information Base.
• Information Conversion Function.
• Human Machine Adaptation.
• Presentation Function.
• Message Communication Function (MCF).

These functional components can be divided into two categories:

• The first five components belong to the first category. These components perform the actual management actions; they do not address problems related to the exchange of management information.
• The last component (MCF) belongs to the second category. This component is associated with all function blocks that require an underlying service for the exchange of their management information. "The MCF is composed of a protocol stack that allows connection of function blocks to DCFs". In many cases the MCF provides the end-to-end functions such as those found in OSI layers 4 to 7.

Recommendation M.3010 contains a picture (Figure 12) to illustrate the relation between function blocks, functional components, the MCF and the DCF.