e carried out via the IP suite in the control plane. For example, the TMN could implement off-line traffic engineering, but in normal condi- tion the routing is performed by the control plane. In practice however, due to the much simpler set of functionalities needed in IP-based networks, it is quite rare that TMN is chosen to implement the central management. The IETF, the Internet standardization consortium, has defined a much simpler standard for the network management, based on the SNMP [56,57]. Three versions of SNMP have been standardized, and to some extent all are in use in deployed networks. It is interesting to note the existence of the so-called bilingual SNMP that support both SNMPv1 and SNMPv2 features. As far as SNMPv3 is concerned, even if the IETF considers it the present version and calls the other versions "Historical," in practice it has not substituted SNMPv1 and SNMPv2. An SNMP-based management system is constituted by the following elements: Network elements. Agents. Managed object: A managed object is a characteristic of something that can be managed. For example, a list of currently active TCP circuits in a particular host computer is a managed object. Managed objects differ from variables, which are particular object instances. Using our example, an object instance is a single active TCP circuit in a particular host computer. Managed objects can be scalar (defining a single object instance) or tabular (defining multiple, related instances). MIB: An MIB is a collection of managed objects residing in a virtual information store. Collections of related managed objects are defined in specific MIB modules. Syntax notation: A syntax notation is a language used to describe a MIB's man- aged objects in a machine-independent format. Consistent use of a syntax notation allows different types of computers to share information. Internet management systems use a subset of the International Organization for Standardization's (ISO's) Open System Interconnection (OSI) Abstract Syntax Notation (ASN.1) to 