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By goodvin | 07 November 2023 | 0 Comments

PON Network Testing and Maintenance

PON Network Testing and Maintenance
Passive Optical Networks (PON) have become a popular choice for broadband network access due to their high bandwidth, scalability, and cost-effectiveness. Proper installation, testing, and maintenance are crucial for ensuring optimal performance and reliability of PON networks. This article provides an overview of key aspects of PON network deployment, commissioning, bandwidth testing, and troubleshooting.
Main Contents of PON Installation and Commissioning
PON installation involves setting up the central office equipment, laying fiber optic cables, installing network terminals at customer premises, and system activation and testing. The main steps are:

1.Install Optical Line Terminal (OLT) at central office - The OLT acts as the master node communicating with multiple optical network units (ONUs). The OLT should be mounted, connected to backbone network, and configured with management software.
2.Lay fiber optic cables - Cables are laid underground or aerially from central office to cabinets near customer locations. High quality single-mode fibers with splits are used for PON construction. Proper cable installation procedures must be followed.
3.Install optical splitters - Splitters divide the incoming fiber into multiple outgoing fibers leading to different ONUs. Splitter ports must match planned number of users and be installed in protective enclosures.
4.Install ONUs at customer premises - ONUs act as slave nodes, communicating with OLT using assigned wavelengths. ONUs should be fixed at proper indoor locations with power supply.
5.Establish connectivity - Optical fibers leaving the splitter are patched to ONU ports. OLT and ONUs are configured for Internet access and services.
6.Activation and OLT-ONU synchronization - The OLT searches and communicates with ONUs to activate them. Encryption keys are exchanged for secure data transfer.
7.Performance testing - End-to-end testing is done to verify desired bandwidth, service levels, reliability, and Quality of Service (QoS) as per service level agreement.
Throughout the installation process, safety precautions, manufacturer’s guidelines, and industry best practices should be followed, along with proper documentation.
Bandwidth Testing of PON Network
PON bandwidth testing is essential to validate actual network performance versus design specifications. Following are key bandwidth tests conducted:
1.OLT port capacity testing - Test maximum capacity of OLT ports by generating traffic up to full port speed e.g. 1 Gbps. Verify OLT is performing as per port capacity without errors or frame loss.
2.ONU speed testing - Validate ONU interface capacity by performing speed tests between OLT and each connected ONU. Verify ONUs attain maximum designed interface speed.
3.End-to-end bandwidth verification - Test actual usable bandwidth between OLT and ONUs under different traffic conditions. Measure throughput, delay, jitter, frame loss.
4.Shared bandwidth testing - Generate multiple bandwidth loads across ONUs to simulate actual customer usage. Validate bandwidth allocation mechanism and QoS under heavy loads.
5.Service bandwidth testing - Test bandwidth per subscribed service like Internet, video, voice. Confirm service bandwidths match subscription plans across simultaneous users.
6.Layer 2/3 performance testing - Evaluate layer 2/3 metrics like switching capacity, routing throughput, multicast efficiency, broadcast containment etc.
7.Traffic shaping and policing - Verify configured traffic shaping and rate limiting mechanisms on OLT and ONUs are performing accurately under different loads.
8.Fault condition testing - Test bandwidth parameters when faults like fiber cuts, equipment failures or restarts occur. Analyze PON resilience under such scenarios.
A comprehensive testing plan should define test cases, expected results, metrics collection and tools required. All test results must be documented for future reference.
Maintenance and Troubleshooting of PON Network
To sustain optimal performance, PON networks require ongoing maintenance and troubleshooting to identify and resolve any issues proactively. This involves:
Preventive Maintenance:
.Regular inspection of cabling, splitters, enclosures for physical damage, bends, connections etc.
.Testing backup power supplies, alarms, monitoring systems.
.Cleaning and replacement of dirty/faulty optical connectors.
.Software/firmware upgrade on OLTs and ONUs.
.Performance monitoring for errors, anomalies.
Corrective Maintenance:
.Link attenuation - Identify excessive loss using Optical Time Domain Reflectometer (OTDR) and restore links.
.Equipment failure - Replace failed OLT/ONU cards, SFPs, power supplies.
.Fiber cut - Locate cuts using OTDR, replace damaged cable segments.
Troubleshooting steps:
1.Link connectivity check - Ping OLT-ONU interfaces to test reachability.
2.Link attenuation testing - Use OTDR to locate points of high loss.
3.OLT-ONU sync verification - Check ONU registration status on OLT. Reinitialize sync if needed.
4.Interface status check - Verify optical light levels, Tx/Rx power levels are optimal.
5.Log file analysis - Examine device logs to identify failure event causes like restarts, errors.
6.Bandwidth performance verification - Conduct speed and throughput tests between OLT and ONUs.
7.Splitter checks - Replace faulty splitters causing very high loss.
6.Layer 2/3 troubleshooting - Verify DNS, IP addressing, VLANs, STP, MPLS and other protocols.
Proactively handling maintenance and troubleshooting ensures continuous uptime and customer satisfaction.
PON deployment is multi-step process requiring careful installation, commissioning, testing and maintenance. Comprehensive bandwidth testing is vital for verifying network performance as per specifications. Ongoing preventive maintenance and troubleshooting ability also determines PON network reliability. With careful planning and execution, service providers can build robust and efficient PON architectures that deliver high-speed broadband access.
Q1. What are the main advantages of PON networks?
A1. Key advantages of PON networks include:
.High bandwidth – PON provides dedicated fiber connectivity enabling bandwidth up to 10 Gbps.
.Scalability – PON allows easy capacity expansion by adding splitters, fibers and ONUs without affecting existing users.
.Long reach – PON provides up to 60km reach between OLT and ONUs.
.Cost efficiency – Only one fiber needs to extend from OLT to the splitter which is shared by many ONUs, reducing fiber deployment cost.
.Security – Data transmission between OLT and ONUs is highly secure through encryption.
Q2. What types of tests are conducted during PON commissioning?
A2. Main PON commissioning and activation tests include:
.Physical layer testing – Optical power levels, link loss measurement using OTDR.
.OLT-ONU synchronization – Ranging, encryption key exchange.
.Service provisioning – Activating Ethernet, VoIP, video and Internet services on ONUs.
.ONU registration – Adding new ONUs, assigning PON ports.
.Bandwidth validation – Speed and throughput measurement between OLT and ONUs.
.Layer 2/3 testing – VLAN, QoS, Multicast, DHCP, Firewall etc.
.SLA compliance – Latency, jitter, error checking as per service contract.
.Long duration testing – Stress testing over 24-48 hours mimicking real-world use.
Q3. How can PON reach be extended beyond 20km?
A3. There are a few techniques to extend PON reach beyond standard 20km limit:
.Optical amplification – EDFA amplifiers boost optical signals allowing PON to reach 60km.
.Extended ONU transmit power – New optical modules provide higher ONU Tx power.
.Wavelength shifting – Shifting 1310nm upstream wavelength to 1550nm band reduces attenuation.
.Fiber Bragg gratings – Reflect specific wavelengths while passing others to extend reach.
.Raman amplification – Boosts signal strength by stimulating Raman scattering in the fiber.
.Higher split ratios – Lowers number of users per PON fiber minimizing splitting loss.
.Tunable lasers – ONUs can transmit at different wavelengths improving power budget.
Q4. What are common causes of high bit error rates in PON networks?
A4. Typical causes of high bit error rates in PON networks are:
.Faulty or dirty optical connectors resulting in signal loss and noise.
.Excessive splitting ratios overloading the PON fiber.
.Low optical power budget due to long reach or high splits.
.External fiber damage from dig-ups or cable cuts.
.Equipment issues like faulty optical modules, drivers.
.Electronic noise from bad splicing, connectors, cross-talk.
.Attenuation from bend losses in fiber cable.
.Software bugs causing encoding/decoding errors.
.Adverse environmental factors like electromagnetic interference.
Q5. How to troubleshoot service disruptions in PON networks?
A5. Steps to troubleshoot service disruptions in PON:
.Check OLT-ONU link status and reconnect if needed.
.Verify optical power levels are within acceptable range.
.Inspect fiber connectors and splices for damage, replace if needed.
.Check ONU registration status on OLT, reinitialize ONU if not registered.
.Analyze PON port statistics for errors, discards, cyclic redundancy check (CRC) failures etc.
.Verify OLT and ONU configurations like VLAN tagging, QoS, DHCP, match on both ends.
.Test service throughput rate between OLT and ONU to identify bandwidth issues.
.Capture traffic and analyze for anomalies – high latency, jitter, packet loss.
.Verify multicast traffic replication if service disruption affects multiple users.
.Check power supply status and replace faulty units.
.Capture log files and identify issues during outage - ONU/port resets, fiber alarms etc.
.Upgrade OLT/ONU software, FPGA, drivers if bug fix available.
.If problem persists, replace the suspected faulty OLT or ONU hardware.
Key is systematic layered troubleshooting isolating issues to specific segments. Follow root cause analysis to pinpoint and fix problems.
Keywords: PON, FTTH, OLT, ONU, Installation, Commissioning, Bandwidth Testing, Maintenance, Troubleshooting, Fiber Optic Networks.

Recommended Reading: PON Network Standardization Work: Driving Interoperability and Global Connectivity

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