control software. Every equipment that is controlled by the network control software is called network element. As far as the geographical configuration is concerned, the network of a tier one carrier can be divided into three areas: access, metro and regional, and core. A high-level scheme of the telecommunication network is reported in Figure 3.1, while a topological scheme of the core network of a U.S. carrier is reported in Figure 3.2 to provide an example of continental core network, while the topology of a pan-European network can be found in Ref. [4]. The access network is the part of the network connecting the access central offices to the users' physical locations. This is the most branched part of the network, penetrating Telecommunication Networks Core network Metro core node Metro access node Residential users Service sources Management system Metro core FE/GbE Enterprise Metro access Data traffic FE/GbE Metro access B/E/GPON DSLAM access Residential Mobile users SDH/SONET business access FIGURE 3.1 Topological representation of metro and access networks. Metro network is composed of a two-level ring topology, while different technologies are used in the access area each with its own topology (PON, ADSL, point-to-point Ethernet, and even direct SDH access are depicted in the figure). Finally, a metro node host- ing content servers is shown: where VoD represents Video on Demand and ISP some other Internet Service Provider content server. Seattle Chicago Boston Kansas City New York City Sunnyvale Newark Denver Washington DC San Jose Atlanta- Los Angeles Dallas Houston Tampa FIGURE 3.2 Simplified scheme of the topology of a long haul North American carrier network. Networks Fundamentals and Present Architectures in metropolitan roads and reaching far into the countryside. The scope of the access net- work is one directional-to collect the signal generated from the end users and convey it to the peripheral network elements, located in the access central offices and in the other direction to deliver the si