How an ISP Network Works: Complete FTTH Guide (OLT, GPON, Splitter, ONU)
NETWORK: OLT SYNCED · GPON ACTIVE · BGP ESTABLISHED
INTERNATIONAL BW400 Gbps
CORE ROUTERS4
ACTIVE PON PORTS1.2k
HOMES PASSED18.5k

How an ISP Network Works: Complete FTTH Guide (OLT, GPON, Splitter, ONU)

From core routers to your WiFi – a technician’s deep dive into fiber ISP infrastructure.

📑 Table of Contents

Speed Test Splitter Calculator Huawei Solutions BDCOM Guide

🌐 1. ISP Core Network

International bandwidth from Tier-1 upstreams enters ISP core routers (BGP/peering). Traffic flow:

🌍 Internet→ Core Router (BGP)→ Aggregation Router

🧩 2. Aggregation Network – Metro Ethernet

Aggregation switches use VLAN transport over fiber rings.

Core→ Aggregation Switch→ OLT

🧵 3. OLT (Optical Line Terminal)

Central office device controlling up to 64 ONUs per GPON port. Functions: registration, DBA, AES encryption.

OLT Features

• ONU management
• Bandwidth assignment
• VLAN tagging

GPON · XGS-PON

PON Interface

TX: +2 to +5 dBm
RX sensitivity: -27 dBm

SC/APC

🔀 4. Fiber Splitters & GPON Power Budget

Split RatioTypical Loss (dB)
1:23.5 dB
1:47.2 dB
1:810.5 dB
1:1613.5 dB
1:3217.0 dB
1:6420.1 dB

OLT TX: +2 to +5 dBm | ONU RX range: -8 to -27 dBm. Use Fiber Splitter Calculator for exact budgeting.

🏠 5. ONU / ONT at customer premises

Converts optical to Ethernet. Brands: Huawei HG8145, BDCOM P1501D, Nokia G-010G.

Fiber drop→ ONU→ WiFi Router→ Devices

⚡ 6. Bandwidth Management (PPPoE & MikroTik)

/interface pppoe-server server
add interface=vlan10 service-name=internet disabled=no

/ppp profile
add name=100M rate-limit=100M/100M

/ppp secret
add name=user1 password=123 profile=100M

BRAS or MikroTik applies queues per profile. Test your speed: Speed Test.

🛠 7. Real ISP problems & fixes

Fiber cut
Use OTDR to locate break
ONU offline
Check power & authentication
High loss
Clean connectors, check bends

📊 8. Complete ISP FTTH diagram

Internet↓ Core Router↓ Aggregation↓ OLT↓ Splitter↓ ONU↓ Router↓ Devices

ISP FTTH network diagram OLT splitter ONU

📡 9. Popular ISP Equipment

TypeModels
OLTHuawei MA5800, BDCOM GP3600, ZTE ZXA10
ONUHuawei HG8145, BDCOM P1501D, Nokia G-010G
RouterMikroTik CCR, Cisco ASR, Juniper MX

🔧 Fiber Installation Best Practices

  • Minimum bend radius: 30mm
  • Always clean connectors with fiber wipes
  • Check signal using optical power meter
  • Use OTDR for long fiber troubleshooting

🧰 10. Useful Tools for ISP Engineers

Fiber Loss Calculator Speed Test Optical Power Converter IPv4 Subnet Calc

❓ Frequently Asked Questions

What is OLT in ISP network?
OLT (Optical Line Terminal) is the central device in a GPON network that connects the ISP fiber infrastructure to customer ONUs.

How many users per GPON port?
Up to 64 ONUs depending on split ratio and bandwidth profile.

What is optical loss for 1:32 splitter?
Approximately 17 dB, ensure ONU RX > -27 dBm.

Speed Test Splitter Calculator Huawei BDCOM