Consolidated ONT Video Overload

Description

The Consolidated ONT Video Overload alarm is used to indicate when an ONT has detected that the signal level of the 1550nm optical wavelength associated with RF video transmission on the PON is above the configured upper threshold. This typically results in poorer video quality as the video receiver on the ONT is typically saturated by the signals levels from the EDFA or Video head end. There is a separate alarm for the downstream GPON signal overload. Signal overload can often cause distortion of the signal at the transmitter and/or saturation of the receiver at the ONT.

If the optical level grossly exceeds the maximum threshold at the ONT, it is possible the set-top-box (STB) is unable to display the video. The optical network budget should be engineered to ensure the proper video signal levels at the ONT. Since with video the optical launch power is known and amplifiers for the 1550nm optical signal may appear at various points in the network. If the optical power of the video signal is high it may be necessary to place an optical attenuation pad of 5 to 10dBm in the optical path, somewhere prior to insertion into the PON. Inserting attenuation into the GPON splitter network would affect the 1310/1490nm wavelengths and so it is better to insert the attenuation prior to the splitter/combiner to the PON. Engineering of the video head-end optical budget is outside the scope of this procedure and must be performed per local practices.

Laser Safety

Warning! Personnel handling fiber optic cables must be trained for laser safety.

Warning! Optical Fibers emit invisible laser radiation. Avoid direct exposure to the beam. Never look into the end of a Fiber or into a Fiber connector on a cable or a device. Permanent eye damage or blindness can occur quickly from laser radiation.

Trouble Clearing

1. Video Injection Level Too High on Multiple ONTs - The Erbium-Doped Fiber Amplifier (EDFA) or video head end is launching the signal with too much power into the PON fiber. If this is happening on multiple ONTs, it is likely that the launch power is the issue. Several solutions exist to this. The optical receive power at the input to the ONT for the 1550nm wavelength must be in the range of +1 to -5dBm (for ONT702/ONT703).
   • Insert a 5 or 10dB pad into the fiber at, or prior to, the splitter/combiner that is used to inject the video signal into the PON to attenuate the video signal. If the pad is placed on the GPON network, rather than the Video network, ensure that the final power levels for the GPON 1490nm downstream and 1310nm upstream levels are still within specification (all signals are attenuated by the pad).
   • Reduce the launch power of the laser from the video head end or the EDFA. Note that this affects all ONTs served by this EDFA/head end.
   • Insert a larger splitter, or more splits, to introduce more attenuation.
2. Video Injection Level to High on Single ONT - If a single ONT is signaling this alarm, and other video customers on the same PON are not, it is possible that the ONT was improperly calibrated at the factory or has a hardware defect.
   • Add Attenuation: If this ONT is a short loop and the other ONTs are long loop, it is possible that a 5 or 10dB pad needs to be added to the path. When doing this, ensure that the final power for the GPON 1490nm downstream and 1310nm upstream levels are still within specification (all signals are attenuated by the attenuator).
   • Replace the ONT (refer to the applicable ONT Description and Installation User’s Guide). If this does not resolve the problem, contact Tellabs Technical Assistance Center (refer to Contacting Technical Support.
3. Video Threshold Too Low  - It is possible that the signal level is fine, but the ONT video threshold is set too low for the ONT and video load head end being used. It may be necessary to modify the threshold for proper operation. Raise the video overload threshold level in the EMS for this ONT. The threshold is found on the ONT Properties dialog, on the RF Video Tab, as shown below.
   
   
    
4. Bad ONT: It is possible that the ONT may be improperly detecting a video overload. If the signal level is within specifications for the video signal, the threshold is set properly and the ONT is still alarming, replace the ONT.

  |  Next