What is the difference between GPON and EPON?

GPON offers higher downstream bandwidth and better QoS. EPON provides symmetric bandwidth at lower cost. GPON supports split ratios up to 1:128 for wider coverage.

Which ONU/ONT is compatible with my OLT?

Our L880G and L801 series ONUs support XPON dual-mode and work with Huawei, ZTE, FiberHome and other major OLT brands. Contact support to confirm compatibility.

What is the difference between SC/APC and SC/UPC connectors?

SC/APC (Angled Physical Contact) and SC/UPC (Ultra Physical Contact) are two common fiber optic connector polish types. The key difference is the end-face angle.SC/UPC: Flat end-face with slight curve, return loss ≥50dB. Used for general-purpose data transmission. Blue color.SC/APC: 8° angled end-face, return loss ≥60dB. Used for RF video transmission (CATV) and PON networks. Green color.They are NOT interchangeable — mixing them can damage the connector end-face.

How do I choose the right fiber optic splitter for my network?

Choosing the right fiber optic splitter depends on several factors:Type: PLC splitters offer better performance for FTTx; FBT splitters suit smaller setupsRatio: Common ratios: 1×2, 1×4, 1×8, 1×16, 1×32, 1×64Package: ABS box (indoor), Mini steel tube (tight spaces), LGX cassette (rack mount)Connector: SC/APC for CATV, SC/UPC for dataFor GPON/EPON FTTH deployments, a 1×8 or 1×16 PLC splitter with SC/APC connectors is recommended.

What is the maximum distance for fiber optic transmission?

Fiber optic transmission distance depends on fiber type and equipment:Single-mode fiber (OS2): Up to 40km+ without amplificationMulti-mode fiber (OM1-OM5): 300m to 550m at 10GbpsGPON: Typically 20km reachEPON: Typically 20kmXGS-PON: Up to 40km1550nm wavelength has lower attenuation (≈0.2dB/km) vs 1310nm (≈0.35dB/km). For standard GPON FTTH, 20km is typical from OLT to ONU.

How do I configure an ONU/ONT for my fiber network?

Configuring an ONU/ONT involves these steps:Connect: Plug fiber cable into PON port, Ethernet to your router/PCPower on: Wait for PON LED to turn solid (optical signal received)Access web: Set PC to same subnet (192.168.1.x), open ONU IP (usually 192.168.1.1)Configure WAN: Set connection type (PPPoE, DHCP, or Static IP) per ISP requirementsRegister: Some ISPs require registration via serial number, LOID password, or MAC address

What is XGS-PON and how is it different from GPON?

XGS-PON (10 Gigabit Symmetric PON) is the next-generation PON technology offering 10Gbps symmetric bandwidth. Key differences from GPON:Speed: GPON = 2.5Gbps down / 1.25Gbps up. XGS-PON = 10Gbps both directionsWavelength: XGS-PON uses 1577nm down / 1270nm up (different from GPON's 1490nm/1310nm)Coexistence: XGS-PON can share the same fiber with GPON via WDMXGS-PON ONUs work with dual-mode OLTs but need an XGS-PON port for 10G speeds. Ideal for 4K/8K streaming, cloud computing, and enterprise use.

How Many Homes Can One OLT Port Serve?

In GPON networks, one OLT port typically serves 32 to 128 homes, depending on the split ratio. A 1:32 splitter is most common for FTTH deployments. With XGS-PON, one port can serve 256+ subscribers. Actual capacity depends on bandwidth per user — if each user needs 100Mbps, a GPON port (2.5Gbps down) handles ~25 users at peak. For our 2-port EPON OLT (L202), each port supports up to 64 ONUs, giving a total of 128 homes per device.

How Is GPON Data Secured on Fiber Optic Networks?

GPON uses AES-128 encryption to secure downstream data. Each ONU receives only its own data — the OLT encrypts traffic with a unique key per ONU. Upstream data is inherently secure because each ONU transmits in its assigned time slot. AES encryption is enabled by default in most OLTs like our EPON/GPON models. For additional security, MAC address filtering and ONU authentication are supported.

Is Fiber Optic Cheaper Than Copper in the Long Run?

Yes. While fiber optic cabling costs 20-30% more upfront, its total cost of ownership (TCO) over 10 years is 40-60% lower than copper. Fiber supports 40Gbps+ bandwidth vs copper's 10Gbps limit, has 25+ year lifespan (copper: 5-10 years), and needs no signal repeaters for up to 40km. For ISPs, the breakeven point is typically 2-3 years. Our single-mode fiber patch cables and splitters provide reliable long-term infrastructure.

Fiber Optic Network Troubleshooting Guide

Fiber Optic Network Troubleshooting Guide: Common Issues and Solutions

29/04/2026 Langzhi Technology

A systematic guide to fiber optic network troubleshooting covering ONU offline issues, optical link failures, signal attenuation, connector contamination, and intermittent connectivity. Learn diagnostic methods and solutions for network engineers.

Common Fiber Optic Network Issues

Fiber optic networks can experience various issues affecting user broadband experience. Timely diagnosis and troubleshooting are essential skills for network运维 engineers.

Issue 1: ONU/ONT Cannot Register (Red Light)

Symptom: ONU PON/LOS LED shows red or flashing, device cannot register to OLT.

Causes & Checks:

Optical link interruption: Measure received power at ONU with power meter. No light or below -28dBm indicates link problem.
Loose connector: Check fiber patch cord is fully inserted with a click.
Contaminated end face: Inspect with fiber microscope, clean with fiber pen.
Fiber break: Use VFL to inject red light and locate leaks.
Splitter port issue: Try connecting to a different splitter port.

Issue 2: Abnormal Optical Power

Low Received Power

Diagnosis: GPON B+ ONU requires -8dBm to -28dBm. Below -28dBm causes failure.

Causes: Long fiber (>20km), high splice loss, tight bends, contaminated connectors. Use OTDR to locate high-loss events.

Excessive Received Power

Diagnosis: Above -8dBm may saturate ONU receiver.

Solution: Add optical attenuator (5dB or 10dB) before ONU.

Issue 3: Slow Speed or Packet Loss

Symptom: ONU registered but slow internet, video stuttering, high game latency.

Check: optical link quality, OLT uplink congestion, ONU configuration (bridge/router mode, QoS), home network (router, cable, WiFi), OLT DBA bandwidth profile.

Issue 4: Specific Service Failure (Voice/IPTV)

Voice: Check FXS port VoIP parameters (SIP server, account, password). Check ONU registration to voice server.

IPTV: Check VLAN configuration (IPTV uses dedicated VLAN). Enable IGMP multicast.

Issue 5: Intermittent Connectivity

Symptom: Network works intermittently, ONU shows red light periodically.

Causes: Loose connector (temperature/humidity changes), borderline optical power, loose splitter port.

Check: Measure power during fault, compare to normal. Log fault times for patterns.

Troubleshooting Flow Summary

Check LEDs: ONU status (PON, LOS, LAN)
Measure power: Optical power at ONU end
Inspect end faces: All connector cleanliness
Locate faults: VFL or OTDR for break/bend points
Verify config: OLT and ONU parameters
Swap test: Replace ONU, patch cord to isolate

Essential Tools

Optical Power Meter
Visual Fault Locator (VFL)
OTDR
Fiber Microscope/Inspector
Fiber Cleaning Pen

Conclusion

Effective fiber optic troubleshooting requires a systematic approach across optical links, device configuration, and environmental factors. Langzhi Technology offers complete fiber optic network equipment with comprehensive technical support.