Hi everybody!
Today, I will explain the main problems with connecting ONU on OLT. OLT correctly works, problems are part of ODN (drop optical cable) and ONU.
Problem:
ONU can not connect on OLT. The most common problem is the optical line (part of ODN – drop optical cable) or ONU.
Reasons:
Problem is on OLT, ODN or ONU.
Mostly, the problem is not with OLT. If we have customers on the same PON PORT, the problem is on part of ODN or ONU. There are many problems with ODN and ONU. Now, I will explain the problem with connecting ONU on OLT when we have users on the same PON PORT.
Procedure:
The first step, we have to check optical power on ONU. To measure optical power we use PON power meter. Min optical power on ONT is -28dBm and max optical power is -8 dBm, because ONU has B+ optical module. It is not good for the optical power to be at the limits of the range. In practice, the range of optical power is about -15 to -25 dBm for stable and correct work (depends on the splitters and distance from the OLT). If optical power in this range, ONU receives the correct optical power for connection.
Otherwise, we have to check the optical line – from ONU to the optical splitter. I will shortly explain how we can fix the problem with part of ODN (drop optical cable). For this check, we can use PON optical meter, VFL (visual fault locator) and OTDR. With PON optical meter we will check optical power on the output port of the optical splitter and determine if it is a problem in drop optical cable, optical connectors or optical splitter. The most common problems are: damaged or bent drop optical cable, dirty optical connectors, problems with bigger optical attenuation from default values of the optical splitter, etc. Instrument VFL can show us possible problems with drop optical cable (damage or bent drop optical cable, or bad splice). OTDR is a very important and useful instrument in every optical network. There are many different models. With this instrument, we can check and see all optical lines (on display instrument show graphics and table). When we fix the problem with the optical line. Optical power will be in recommand range and ONU will be connected.
If there is a problem with ONU (OLT and ODN are correct), we have to check:
Is ONU powered on? Does adapter for power supply work correct?
Is there an authentication conflict for ONU?
Is problem with hardware (e.g. optical module)?
Thank you!
