 the SONET layer with a void load that has to be transported in any case. Moreover, this strategy makes it impossible to use at best SONET grooming capabilities that are embedded into SONET DXC and ADM. For these reasons, a more effective adaptation layer has been defined between IP and a lower TDM physical layer that could be SONET or even OTN: the General Framing Protocol. Telecommunication Networks Client SONET ADM Router Router-router virtual connection POS path SONET ring 1 SONET- ring 2 SONET SONET SONET SONET SONET SONET SONET Transit router router router FIGURE 3.48 Representative topology and layering of an IP over POS network. 3.3.2 IP over Next Generation SONET/SDH To overcome the limitations related to the use of Packet over SONET while maintain- ing the familiar SONET performances, an important group of carriers mainly in North America are pushing toward a new generation of SONET/SDH equipment, more suitable for delivering data-based services [62,63]. These equipment should be based on two main technologies: a new and very efficient packet encapsulation procedure (the general framing procedure [GFP]) and an embed- ded mechanism to manage the transmission bandwidth in a dynamic way to increase the exploitation efficiency of the physical layer resources. 3.3.2.1 General Framing Procedure GFP is a powerful way to multiplex different packet-oriented formats on the same TDM frame. Differently from POS, GFP does not rely only on the use of monolithic SONET frames, but defines a complex adaptation that is sufficiently flexible to allow both efficient multi- plexing and effective grooming to exploit at best the transport platform. GFP is conceived for application in high-capacity networks and for transport of a plural- ity of data formats, some of them datagram based such as IP, others frame based such as Ethernet or other datacom oriented formats such as the Fiber Channel. A first consequence is that WDM is assumed to exist as transmission facility. Networks Fundamentals and Present Architectures 100 Mbit/s