Appendix A
Data Flow in a PON
Fig. A.1 represents data flow in any passive optical network (PON) or similar systems such as DOCSIS; it applies to just about any point-to-multipoint system. In the downstream direction, the optical line terminal (OLT) puts out continuous data with no gaps. In this simplified diagram, there are three optical network terminal (ONTs), each of which gets its downstream data during a time slot of variable length, depending on how much data is available for that ONT and how much bandwidth the subscriber is allowed. The data for each ONT are preceded by a header (not shown) embedded in its data, which identifies the ONT and usually the port on the ONT which is to receive the data. It is essential that the downstream data ...
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