GPON equipment, as an emerging optical access device, is now used on a large scale in many areas. In order to ensure the stable and healthy operation of the equipment, it is necessary to pay attention to the standardization of daily routine maintenance work, and to keep abreast of the equipment operation through routine maintenance in order to discover and solve various hidden problems in GPON network in time.

GPON network is composed of OLT, ONU and ODN.

OLT provides the interface between the network side and the core network for the access network, and connects with each ONU through ODN. As the core functional device of PON system, OLT has the functions of centralized bandwidth allocation, control of each ONU, real-time monitoring, operation and maintenance management of PON system. The following aspects are to be focused on in GPON network maintenance work.

Daily maintenance of OLT and ONU devices in GPON networks

(1) Check the operating status of the single-board, and timely find the abnormal state of the single-board to avoid abnormal service for a long time. If the single-board status is abnormal, check whether the single-board is in the specified slot at this time; if it is not in the specified slot then it may be that the single-board is unplugged but not removed from the system; if the single-board is in the specified slot, then you can test and determine whether the single-board is faulty by re-plugging the single-board, replacing the slot, replacing the single-board, etc.

(2) Check the system log information, you can timely find the operations that have serious impact on the stable operation of the system (such as Reboot, Rollback, Load and other commands). If abnormal operations are found, the person operating and the reason for the operation need to be verified. If illegal user login is found then it is necessary to readjust the access control list of the device and modify the login password regularly.

(3) Check the system alarm information to keep abreast of the equipment alarm status, and perform necessary maintenance on the system according to the alarms to prevent failures and accidents.

(4) Check the status of the uplink interface. uplink interface of GPON equipment is very important, used as the system uplink, daily maintenance to pay close attention to the status of the uplink interface. Under normal circumstances the working mode of the docking port should be consistent. If the result of port self-negotiation is half-duplex status, it is necessary to confirm whether the working mode of the ports on both sides of the docking is the same. If there is an increase in CRC error messages, it is necessary to check the working mode of the line and the ports on both sides.

(5) Check the status of the PON port. the PON port as the interface to the ONU, the status is very important, the daily maintenance should pay close attention to the state of the PON port. Under normal circumstances PON port status is ON, CRC error messages are not increased. If the port status OFF state appears, it is necessary to confirm whether the docked ONU is normal. If there is an increase in CRC error messages, it is necessary to check whether the optical path and splitter, etc. are normal.

(6) Check the fan status to confirm that the equipment can dissipate heat normally to avoid abnormal system operation due to high temperature. If the fan status is found to be abnormal, it may be a fan monitoring configuration error or fan hardware failure. It can be reconfigured. If the failure persists after reconfiguration, the fan operation status should be checked on site.

(7) Check the environment of the machine room. The environment of the server room has a significant impact on the stable operation of the equipment. Daily maintenance should pay attention to the changes in the environment of the server room to ensure that the environmental indicators meet the requirements for the stable operation of the equipment for a long time. Room temperature: 15℃～30℃, room humidity: 40%～65%, power supply voltage: -38.4V～-57.6V.

Routine maintenance of ODN in GPON network

ODN passive optical network is the physical connection part from OLT end to ONU end, the failure of fiber optic cable, splitter or skin fiber cable will cause the failure of users at ONU end. Therefore, you should pay attention to the maintenance of ODN network in general.

(1) Splitter maintenance: regularly test and record the redundant ports of splitters, and mark the problematic ports.

(2) Skin cable maintenance: do a good job in the building skin cable maintenance management, regular inspection of the building, timely detection of hidden problems and deal with them, to prevent the occurrence of obstacles caused by construction or rodent bites and other reasons.

Daily maintenance of network management system in GPON network

Network management system is an important and effective technical support means in GPON network maintenance. Under normal circumstances the network management server must not be shut down at will to prevent infection of computer viruses and to conduct virus checks regularly. It is not allowed to perform operations on the network management server that are not related to maintenance, or to use tapes, CDs and USB drives that are not related to maintenance. At the same time, the network management system must strictly implement the password confidentiality system. Regularly check the setting of system operation authority, including password information. Network management personnel need to periodically inspect the operation of the manufacturer’s network element management system, including the normal communication between the network element and the monitoring system, the normal configuration of the network element data, and record the use of the network element management system login.

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Daily maintenance of outdoor equipment in GPON network

For outdoor cabinets, maintenance personnel must conduct regular inspections, and should arrange inspections immediately after bad weather. The outdoor inspection mainly includes the following: the appearance of the chassis, rustproof paint, danger notices and other markings are complete, the inlet and outlet are sealed tightly, the box is free of debris, keep the box clean and tidy, the grounding cable is in good contact, the lightning protection switch is in normal condition, the box has good heat dissipation, power lines, subscriber lines, fiber optic wiring is neat and standardized, etc.

GPON network common fault analysis

Optical network layer common faults in the GPON network, optical network layer faults mainly include fiber / optical cable line failure, OLT / ONU optical module failure and abnormal light-emitting ONU failure, etc.

(1) fiber/optical cable line failure. Common optical fiber / optical cable line failure can be divided into the following three categories: fiber failure, such as broken fiber, bending, etc.; fiber attenuation abnormalities caused by fiber aging; fiber connection abnormalities, including connector off, connector loose / contaminated, fusion point damage, splice box into the water, etc.

(2) OLT/ONU optical module failure. OLT/ONU optical module failure that OLT/ONU optical transceiver failure, OLT/ONU transceiver common failures can be divided into four categories: abnormal transmit optical power; bias current abnormal; abnormal operating temperature; abnormal operating voltage, etc.

(3) abnormal light-emitting ONU failure. Abnormal light-emitting ONU, that is, those in the GPON system in the time slot not authorized by the OLT light-emitting ONU, is a typical fault in the GPON system. Abnormal light-emitting ONU can be divided into two categories: abnormal emission but normal reception, known as controllable light source, that is, the OLT can turn off the laser by giving specific instructions to ONU to stop the light, so as to achieve a certain degree of fault troubleshooting; emission and reception are abnormal, such ONU is called uncontrollable light source, can not be troubleshooting through remote diagnostic means in the GPON system, in general, requires manual on-site troubleshooting. Due to the topological characteristics of PON with multi-point access, abnormal light-emitting ONU will lead to a significant reduction in system reliability and network congestion, and in serious cases, even the entire PON system can be paralyzed. Therefore, the troubleshooting of abnormal light-emitting ONU is particularly important for PON systems.

Service application layer common faults

GPON system has full service access capability for data, voice and video, and can provide broadband Internet access, IP telephony, HD video and other broadband and narrowband services to end users. When the service is opened, the service upstream and downstream bandwidth, QoS parameters, VLAN parameters, multicast service parameters, etc. need to be configured on the GPON system, and these parameters should match with the upstream BRAS parameters and the parameters of the downstream home gateway equipment or enterprise switch equipment to ensure normal service. In GPON system, service application layer failures include but not limited to the following aspects: incorrect configuration of upstream and downstream service bandwidth parameters; incorrect configuration of QoS parameters; incorrect configuration of VLAN parameters or mismatch with BRAS configuration; incorrect configuration of service parameters; incorrect configuration of ACL; service failures caused by security policy; incorrect configuration of upstream and downstream interface parameters, such as full-duplex/half-duplex mode, LACP protocol parameters, etc.

Other common faults of GPON

In the PON network, in addition to optical network layer faults and service application layer faults, there may also be some faults caused by the working environment, power supply or software and hardware, which are commonly found in the following cases: faults caused by power supply, including insufficient power supply and unstable voltage; faults caused by high or low ambient temperature; faults caused by mismatched software and hardware versions; faults caused by electromagnetic interference. From the GPON network application problems that have been found so far, the faults in GPON network in networking applications mainly come from the optical network layer (i.e. optical link) and the service application layer.

Extended Reading: Understand GPON Technology – Cisco