You need a different point of view with regards to GPON FTTP compared to FTTC/ADSL…the total bandwidth is around 2.5Gb download ( ignoring upload for now ) , downstream ‘data’ is broadcast to all ONT’s on the PON from the OLT , so your ONT ‘receives ’ every downstream data packet , as does every other ONT on the PON ,this aggregated data maxes out at 2.5Gb if the demand is such , if no one is consuming data ( so at ‘idle’ so to speak ) then it’s not 2.5Gb but whatever the demand is at that particular instant in time , your ONT is only interested in the data addressed to it , ignoring everyone else’s ‘data’ , if you ran a speed test on a 500Mb profile , and the total aggregate demand, including your speed test were less than 2.5Gb then your speed test result would be ( near enough ) your profile speed , this is the normal state .
Your ONT is set to a profile ( say 500Mb ) next door could be 150Mb , the data ‘hitting’ both your ONTs is identical, in content and speed , your ONT provides the limit , in this example the neighbour is limited to 150Mb by the ONT , you 500Mb by your ONT , even if you are the only two ONT connected to the PON , this 2.5Gb is shared , regardless if there being one ONT or 30 ONT’s , if there were 30 ONT connected and each were simultaneously downloading multi Gb files ( not very likely ) that is less than 84Mb each ( ignoring dynamic bandwidth allocation for now ) , so a speed test in these conditions, the speed to hub ( what you call the line speed ) won’t show the profile speed , it will show the actual rate data is being received, but generally 2.5Gb is more than sufficient so in all but extreme conditions a speed test will be the profile speed less any Ethernet overheads , so on a 500Mb profile, around 480Mb .
Because the chances are there will be many fewer than 30 ONT on the PON , and the majority will be ticking over consuming (relatively) tiny amount of bandwidth, and the ‘bursting’ nature of data transmission, 2.5Gb is more than plentiful, so that a 900Mb customer can be guaranteed 700Mb .
TBH , in your case , I would suggest you need to either borrow someone else’s equipment that doesn’t have an issue on their own FTTP service , or take your kit to an address with OR FTTP and ‘prove’ it performs correctly, (or confirms the problem moves with your kit) as stated earlier your issue seems virtually identical to a recent post on another forum , even to the point of using the same manufacturer of equipment.
I think the least likely problem will be with the PON itself as every user would suffer the same problem as you , it’s conceivable that your ONT is faulty , and if you have reported a fault , a change of ONT would be useful if simply to eliminate it as the cause.
