Functional representation of a GPON OLT. The New Access Network Systems and Enabling Technologies The ranging protocol needed for the correct synchronization of all the signals sent toward the splitting center is also part of the interface functionalities. Besides this transmission function, the core shell contains the so-called OLT Cross Connect. Originally, it was a digital cross connect since in the OLT, the SDH/SONET stan- dard was applied. In more modern OLTs, it is common for a carrier class switch to function as a cross con- nect inside the OLT. It has the role of grooming all the traffic coming from the user with lines that terminates in the OLT SO as to best exploit the backhauling lines of the OLT. The DBA is managed in this part of the OLT. The common shell includes all the management and maintenance functions, and from a hardware point of view, the power supply also belongs to this shell. Finally, all the functionalities related to data back hauling are located in the service shell. Among them, we can note the termination of the core network signaling and the interfaces with the backhauling lines. Also, the functional structure of the ONU, plotted in Figure 11.6, can be divided in the same shells, where now the service shell is toward the home network and the user appliances. The partition of the main ONU functions among the three shells is quite recent and is shown in Figure 11.6. Service Customer interface Transmission function service multiplex interface multiplex function function function Core shell Common shell Service interface Power function supply function function Service shell FIGURE 11.6 Functional representation of a GPON ONU. Telecommunication Networks 11.2.3 NG-PON Project and the GPON WDM Overlay One of the main targets of tier one carriers is to burst individual fruition of services with respect to broadcast fruition (that in the field of television means VoD with respect to Broadcast IpTV). This is because broadcast can also be done, even with a smaller bandwidth, by means of satelli