488 Mbps traffic and readily sup- ports frame relay, POS, and ATM networks. It offers low-voltage differential signaling (LVDS) inter- faces to the backplane for SONET/SDH ADM and crossconnect functions. It also supports either a synchronous or asynchronous generic microprocessor interface for control purposes. The TDAT is almost identical, but lacks the crossconnect and ADM functions of the full-featured TADM. The TADM among other things provides for the encapsulation and de-encapsulation of packet and ATM streams into and out of SONET/SDH payloads. It interfaces with the NPU-based line card using standard Universal Test and Operations PHY Interface for ATM (UTOPIA) or enhanced UTOPIA interfaces (the latter is dubbed PLATO by Agere). As shown in Figure 16.4, the TADM interfaces with the fiber optics either directly to a transceiver, in the case of OC3/12, or to a transponder, in the case of OC-48. For OC-12, the TADM can talk directly to four separate transceivers, interfacing with them with one differential pair for each optics at 622 MHz. For OC-3, the TADM can also talk directly to four separate transceivers, interfacing to them with one differential pair for each optic at 155 MHz. For OC-48, the TADM talks to the transponder with 16 bits operating at 155 MHz. The transponder then performs the serializer/deserializer functionality to interface to the 2.488 GHz optics. Incidentally, our switch/router designer has also noticed that MAC controllers are included in the Agere NPUs, which ultimately makes the board design work much easier. The approach just described based on the common use of the TADM chip is interesting as the com- munication will have to be handled properly at the midplane. The midplane will end up probably look- ing like a star and the backplane will need to contain serdes-based links that might run in the center height of the cards. At the same time, it seems obvious to our designer that the main physical chal- lenge with the system design around the switch fabric card(s) is not going to be so