The Ranging Problem

Abstract

The application of cell based transmission techniques over a passive optical network (PON) with a tree architecture, using intensity baseband modulation and regular time division multiplex techniques, will cause collisions in the network. Collisions occur when cells from different optical network units (ONUs), transmitted upstream, arrive at the same time, or partially overlapping in time, in the passive splitting/combining points of the optical network. These colhsions are caused by the differences in optical path lengths in the different branches. These collided cells are propagated further upstream until they arrive at the optical hne termination (OLT). The OLT cannot properly detect the bits of the collided cells, and a large number of bit errors and possibly cell loss will occur.