10.0 GPON Rogue ONU Detection
A GPON network comprises of an optical line terminal (OLT) that may typically interact with 32 optical network units (ONU) with a
maximum of 128 ONUs. The OLT manages upstream communication by assigning a time slot for each active ONU in order to
prevent transmission collision between active ONUs. In addition to unique ONU timeslots for transmission, each GEM frame also
contains a blank BWmap interval which can be used during the ONU activation process to allow the ONU S/N to be broadcast
without issue.
The two most common failure modes in any PON network are:
1. ONU failed to stop transmission at its expected BWmap stop time.
2. Time-related malfunctions or issues which are harder to detect and isolate.
GPON network data is transmitted using a scrambler without any redundancy. CRC only exists in the last frame field of any packet,
and packets can be spread over several grants (US transmission from a ONU). The ITU-T G.984 GPON standard does not provide
any specific method to detect a rogue ONU in the network. A rogue ONU is an ONU that goes out of control and works in the
continuous or irregular mode. Time related issues can include the following:
1. ONU failed to stop transmission at its expected BWmap stop time.
2. ONU begins transmission pre-maturely.
Current ONU Rogue status can be viewed in the OPM result display.
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