9.1 Downstream Alarm/Errors
9.1.1 LOS
LOS
means 1490nm Loss of Signal is detected. In an active GPON network, the 1490nm DS is always transmitting.
LOS Troubleshooting
1. Verify GPON fiber is inserted in the To OLT test port.
2. Check the optical fiber.
If the optical fiber is not connected properly, clean/inspect/reconnect the optical fiber again and make sure the fiber is
connected correctly and securely. You should not be able to pull the connector out of the coupler with a gentle pull on
the cable itself.
Make sure the mated connector types match. Do not mate a blue color connector with a green connector.
If the optical fiber is aged, bent, or damaged: replace the optical fiber.
If the connector of the optical fiber is not clean, clean the optical fiber.
If the connector of the optical fiber is scratched or pitted, replace connector.
9.1.2 LOF
LOF
means 1490nm DS Loss of Frame occurred.
9.1.3 LCDG
LCDG
means Loss of Channel Delineation for GEM detected previously but not anymore. The System generates this alarm when
delimitation of the GEM frame header is incorrect. The OLT detects HEC check errors of the GEM header in consecutive frames.
LCDG IMPACT
: Loss of frame (LOF) in the system, and the ONT goes offline.
Possible LCDG Causes
: Optical fiber is faulty or ONT is faulty.
LCDG Troubleshooting:
1. Check the optical fiber.
If the optical fiber is not connected properly, clean/inspect/reconnect the optical fiber again and make sure the fiber is
connected correctly and securely. You should not be able to pull connector out of the coupler with gentle pull on cable
itself.
If the optical fiber is aged, bent, or damaged: replace the optical fiber.
If the connector of the optical fiber is not clean, clean the optical fiber.
If the connector of the optical fiber is scratched or pitted, replace connector.
2. If the ONT is abnormal, reset or replace the ONT.
9.1.4 BIP- Bit Interleaved Parity
Each GPON Transmission Convergence (GTC) frame contains Physical Control Block downstream
(PCBd) and payload:
PCBd contains sync, OAM, DBA info, etc.
Payload has GEM partitions (ATM partitions removed from standard) but some vendors continue to include either one or both
types of partitions.
Downlink frame fixed 125
μ
s frequency is 8000Hz and size is 38,880 bytes at 2.488Gbps rate.
GTC payload can have 2 sections:
GEM partition (current standard)
ATM partition
Looking at the Downstream and Up Stream Frame Structures below, BIP - SONET/SDH-style Bit
Interleaved Parity of all bytes since last BIP (1 Byte) is visible.
MTTplus-420_User_Manual_RevC00
Page 47 of 75
