w TCP/IP Works in a Modern Network, Morgan Kaufmann Series in Networking, Burlington, MA, s.l., 2008, ISBN-13: 978-0123745415. Networks Fundamentals and Present Architectures 3.1 Network Infrastructure Architecture The telecommunication network is perhaps the most complex infrastructure deployed by humankind. It is pervasive, reaching almost all parts of the world, and exploits a wide set of different technologies. In this chapter, we will depict the current situation of the most advanced networks, con- sidering only wire-line access. Wireless access is another important part of the telecom- munication network, but it is out of the scope of this book. Not all the carriers reach the same level of technology. Some carriers are not able to invest the required capital expenditure (CAPEX) to be technology updated in all parts of the network; others simply do not experiment a push from their own market toward the use of the most advanced technology. In describing the present day's situation, we will also review some fundamentals of the telecommunication networks theory to give the reader all the needed elements to become acquainted with the object of this chapter. 3.1.1 Network Topology A telecommunication network spans a wide geographical area and is composed of differ- ent types of equipment. The basic infrastructure is composed of fiber cables or, in the access area, of copper pair cables. It is no mean task to arrange thousands of kilometers of optical fibers in an under- ground or submarine cable SO that it resists both environmental erosion and shocks due to accidents like civil works near the cable location. A detailed discussion of cable technol- ogy is reported in the following bibliographies [1-3] and some information on fiber optics cables is contained in Chapter 4. All the other equipment composing the network has some degree of onboard intelli- gence, generally provided by an equipment control card. This intelligence is needed to perform remote monitoring and configuration of the equipment via the network 