If an ONT fails to register with the OLT, this does not automatically mean that the ONT is faulty. The cause may lie at various levels: with the fibre optic cable and the optical signal level, with the assignment to the correct PON, with ONT authentication, or in the network configuration. Systematic troubleshooting therefore begins at the physical layer and then works its way up to registration and the IP connection.
Is the PON optical level sufficient?
A selective or filtered PON power metre can measure the relevant GPON and XGS-PON wavelengths separately. This makes it possible to determine whether the respective optical signal is present at the connection and what the signal level is.
If the level is abnormal, the optical link should first be investigated further. If, on the other hand, the optical layer appears normal, troubleshooting can continue at the next level.
Am I connected to the correct PON?
A sufficient optical level alone does not necessarily mean that the connection is assigned to the intended PON branch.
The PON ID can be used to verify the assignment to the PON. Particularly in installations with many fibres or central distribution points, this allows incorrect fibre or port assignments to be detected at an early stage.
Why isn’t the ONT registering?
If the fibre, signal level and PON assignment are all normal, the registration process itself can be investigated.
Possible causes may then lie, for example, with the authentication, configuration or activation of the connection. At this stage, it is helpful to distinguish the customer’s ONT as a possible source of error from the network side.
How does an ONT simulation help with troubleshooting?
In an ONT simulation, the tester takes on the role of the ONT and attempts to establish a connection with the OLT itself. This allows you to check whether the connection can be established independently of the customer’s ONT.
If the tester registers successfully, this indicates that the optical link and the network side are functioning correctly in principle, and that the cause may lie with the customer’s ONT or its configuration.
If the ONT simulation also fails, troubleshooting can be focused on authentication, OLT configuration or network activation.
Are the IP connection and services working?
A successful ONT registration does not automatically mean that the connection is fully operational. Once a connection has been successfully established, tests at higher protocol levels can therefore be carried out.
Depending on the specific scenario, the following functions can be checked:
- IP connection
- Upload and download
- Ping
- Internet access
- IPTV
- VoIP
This allows the diagnostic process to be carried out from the physical fibre-optic connection, through PON registration, right through to the actual services.
How do ARGUS testers assist with PON troubleshooting?
Using the relevant ARGUS measurement functions, several steps of PON diagnostics can be combined within a single tester: fibre inspection, selective level measurement, PON ID, ONT simulation, as well as IP and performance tests.
This enables the technician to narrow down the cause of the fault step by step, rather than simply stating: ‘The ONT is not registering.’
The crucial question is rather: Does the cause lie in the fibre-optic link, the PON mapping, the ONT, or on the network side?
