, carrier class Ethernet is currently considered as essen- tially a metro network technology, but in the metro area it is experimenting a strong push especially in Europe and in a few Far Eastern countries. 3.4 Comparison among Different Core Architectures In this section, we will try to compare the core network architectures we have considered both under a functional and from a CAPEX point of view. As all the similar exercises numerical results have to be considered in their qualitative meaning, depending on technology and also on the even more unstable market situation that strongly influences the economic part of the comparison. We will try to reduce these dependencies by using a set of countermeasures. First of all, we will work with network costs for the network vendor, thus eliminating the impact of the vendor margin that is strongly customer dependant. Moreover, all the results will be reported in a relative form, SO that in the absence of tech- nology breakthroughs, the market-related variation is partially compensated. As a matter of fact, in the absence of relevant technology changes, the price of products used for the same application varies almost in the same way. The next step is to recognize that in order to carry out a significant comparison, sin- gle equipment cannot be compared out of a network environment, but networks built from different technologies have to be compared looking at both their cost and their functionalities. 3.4.1 Architectures Functional Comparison Before the economic comparison, it is important to set clearly the relationship among the different architectures we have considered in terms of performances. A too-low-performing architecture would force the carrier to ask for the lacking per- formances from other segments of the network (e.g., the upper layers) SO that the CAPEX saving could be illusory if the whole network is considered. 3.4.1.1 Framing Efficiency The original reason why POS was introduced to substitute IP over ATM over SONET was the frame efficiency. As a matter 