an work with high frame efficiency but only in tandem with a suitable upper layer and in conditions of high traffic. The greater framing efficiency for every client speed compatible with a core network is realized by GFP with VCAT. In this case, there is the greater frame flexibility and high Telecommunication Networks TABLE 3.7 Comparison among the Frame Efficiency of Different Adaptation Layers between the IP Network and the Physical Layer Next Generation SONET Efficiency Efficiency Mapping Mapping Ethernet 10 Mbit/s VC-12-5v Fast Ethernet 100 Mbit/s VC-3-2v 1.25 Gbit/s VC-4-16c VC-4-7v 10GbE (WAN PHY) 9.953 Gbit/s VC-4-64c VC-4-64v Digital video 270 Mbit/s VC-4-4c VC-4-2v Serial digital HDTV 1.485 Gbit/s VC-4-16c VC-4-10v SDH STM-16 2.488 Gbit/s VC-4-17v SDH STM-64 9.953 Gbit/s VC-4-68v efficiency is reached even in the absence of efficient multiplexing and grooming in the upper layer. The efficiency of POS, next generation SONET, and OTN are summarized in Table 3.7 [66] in different conditions. 3.4.1.2 Network Scalability: Core Network The ability of a network to expand its capacity in pace with an increasing demand without the need of drastically changing its architecture is called network scalability. There are essentially two ways of scaling a network: adding traffic on the same topology or adding nodes and/or transmission systems, thus modifying the topology [67]. From the scaling point of view, SONET-based architectures have a not SO good perfor- mance. As a matter of fact, adding new traffic on existing links in SONET-based architec- tures can easily bring the need of installing new SONET equipment due to the saturation of the elements already present. This could be mandatory, for example, when a new wave- length is to be turned on. As far as the addition of new topology elements is concerned, while the increase of traf- fic can cause the need of using unused fibers present in cables to deploy new transmission systems, the addition of a completely new core node is not a frequent event. Exception in this