Fibre cut or power cut? How an ISP NOC can tell in minutes
Twenty ONTs on one PON go offline at the same moment. Is a cable cut somewhere, or did the electricity go off in that street? The answer decides whether you send a splicing team at night or simply wait. Getting it wrong costs either hours of outage or a wasted call-out.
What the OLT tells you
A GPON OLT records why each ONT went offline. The two causes that matter here are:
- Power fail (dying gasp): the ONT had time to report that it was losing power. Typical of power cuts and load-shedding.
- LOS (loss of signal): the ONT simply disappeared from the fibre. Typical of a cut, a broken connector or a bent cable.
Many ONTs going down with dying gasp at the same time almost always means a power problem in that area. Many ONTs going LOS together points to the fibre.
Why it's not that simple
Real networks are messy. Some ONTs don't report power loss at all, load-shedding repeats on a schedule, and when an OLT or its power goes down every PON looks broken at once. Reading all of this by hand at 2 a.m. is slow and error-prone. A good alarm system sorts it out for you, so the NOC sees one clear alarm instead of hundreds of red lines.
What the NOC really needs to know
- Is it a fibre problem or a power problem?
- Is it one PON, or the whole OLT?
- Roughly where is the cut, and which street should the team go to?
- Which customers are affected, so support can answer calls?
- When are customers back, so the team knows the repair worked?