Separating the management network from the telecommunication network prevents potential problems with fault management: even in the case of a failure in the telecommunication network, management will still be able to access the failing components. TMN has thus better fault management capabilities than management approaches like OSI and SNMP. Unfortunately, the separate management network requires additional equipment and transmission systems. Costs are thus higher. However, failures can also take place in the management network and therefore it will be necessary to manage the management network too (meta management). This introduces additional costs.
There is also another reason to introduce a separate network for management. Telecommunication networks, like the one for telephony, provide an isochronous type of service. Such type of service does not correspond to the asynchronous (packet oriented) type of service that is required to transfer management information. A separate management network must thus be introduced to manage the telephone network. The better fault management capabilities of the separation are in such case only a secondary consideration.
As opposed to TMN, OSI and SNMP are particularly aimed at management of datacommunication networks. The type of service provided by such networks is usually the same as the type of service required for the exchange of management information. With datacommunication networks, and thus in case of OSI and SNMP, a serious consideration is needed whether the advantages of a DCN outweigh its costs.