represented, that from A to Z is shown). The additional signal path created by the drop and continue capability of the ADM belonging to ring 1 located in node X is represented with a dashed line. In the working mode, the signal passes in node X from ring 1 to ring 2, but if the connection between the two ADM in node X fails, the signal is also sent to node Y, where it is passed from ring 1 and ring 2 to be sent again to node X along the ring 2 fiber. Up to now we have described the features of a standard SDH/SONET ADM. This kind of machines is more and more substituted, especially in north American net- works, by the so-called Next Generation SONET equipment (also called Multi Service Platforms MSPP) [56,66]. Telecommunication Networks First ring First ring OC192 line OC192 line interface interface OC192 line OC192 line interface STS 3 interface OC192 line switch OC192 line interface fabric interface OC192 line OC192 line interface interface Second ring POS or GFP adaptation Second ring SONET drops Embedded carrier STS 3, , STS 1 Ethernet switch Ethernet clients SONET clients FIGURE 7.51 Functional scheme of an OC-192 four fiber MSPP. An MSPP ADM has all the features of a standard ADM, plus a set of completely new functionalities that put it apart as a machine performing both circuit and packet switching on the same platform. There is quite a variety of design for MSPP ADM on the market, just for a reference an example is reported in Figure 7.51. Two main differences are immediately evident between the ADMs in Figures 7.49 and 7.51: 1. The MSPP ADM has a switch fabric with all the typical DXC characteristics that allows more than one ring to be managed both independently and, if it is benefi- cial, consolidating and grooming the traffic among different rings. 2. The MSPP ADM incorporate besides traditional SONET drop interfaces also a packet over sonet (POS) or a generic framing procedure (GFP) adaptation inter- face and a small capacity Ethernet switch that allows it to be directly interfaced with carrier class 