OC Decode

The Optical Control (OC) field is part of the downstream Physical Layer OAM (PLOAM) channel defined in ITU-T standards. It is the initial downstream control information an ONT receives from the OLT. It carries broadcast control information that every ONT must decode before it can synchronize to the PON and monitor upstream/downstream power levels.

Use the OC Decode screen to interpret PLOAM messaging context and assist in reading the PON analyzer's core input before chasing upstream issues. Color-coded for visibility, it is broken down by PON-ID Type, PON ID, Reserved, TX Optical Level Reference, and Transmit Optical Level.

To see the OC Decode screen, select Tools and then select OC Decode.

OC Decode screen

 

• PON-ID Type: Flag that tells the ONT how to interpret the PON-ID that follows. It's used to ensure the ONT decodes the correct format e.g. GPON, XG(S)-PON.

• PON-ID: Unique identifier for PON segment used to confirm connection to the correct OLT and accept downstream information from it, while ignoring information from foreign OLTs.

• Reserved: Reserved bits are defined by standard and should be ignored by ONTs unless explicitly supported.

• C (TX Optical Level Reference): Part of the ONT initial ranging process, it is a flag that provides a downstream power reference that the ONT uses when calculating its upstream launch power during activation and power leveling.

• TOL (Transmit Optical Level): Important Flag for maintaining upstream stability. It tells the ONT the target upstream launch power it should use to ensure proper burst reception at the OLT, maintaining receiver dynamic range and upstream stability.