ication facility to con- nect different parts (that is called the DCC: Data Communication Channel) and of a spe- cialized control plane to use this facility correctly. Frequently, the capacity designed for the overhead of the various layers is also used to implement the DCC. The most common solution is to exploit the Dx bytes embedded into the SDH/SONET MS overhead. Another, less used, possibility to implement the DCC if WDM is present, is using a part of the capacity of the service channel that WDM systems provide on a wavelength on the edge of the standard WDM comb. However, these are not the only possible solutions, and even a completely separated data network can function as DCC. The DCC is managed by an OSI-like control plane that is called Q3 and that is optimized to interface TMN objects. Taking into account all the elements we have mentioned, a possible scheme of a TMN is represented in Figure 3.46 where the operating system (OS), the user interface (UI), and management information base (MIB) represents respectively the operating system of TMN workstation, its User interface and the TMN database, while NE represents the net- work element, Qx a simpler protocol stack with respect to Q3, and Qa is the adaptation function for the connection of elements that does not present a TMN standard interface [55,56]. In this very brief description, we have considered the standard ITU-T architecture of the TMN, but this is not the only used technology. Different vendors can apply other technology solutions, deviating from the standard. Examples of this type are the Simple Network Management Protocol (SNMP)-based man- agers that are constructed around the SNMP that have been quite a success in the United States. Networks Fundamentals and Present Architectures 3.2.9 Central Management in IP Networks In its intention, the TMN standard is defined to be applicable to every kind of network. If TMN is to be applied to a data network based on the Internet model, a few of its function- alities have to be disabled, since they ar