FOA Guide


Migration from GPON to XG(S)-PON

Vladimir Grozdanovic

Today, FTTx PONs are the most popular access networks. They have gained great popularity in the last ten years due to the great demands of subscribers for high data rates and the low cost of passive optical networking equipment.

In general, PON networks offer a reliable, high-quality, and economical solution. Comparing PON and access networks implemented with copper cables (HFC, xDSL, etc.), there are a number of advantages. The most important advantages are lower attenuation, high bandwidth, immunity to interference, and low cost of passive optical equipment.


The historical development of the ITU PON standard started with APON (ATM-PON), after that BPON, then today's current standards GPON, XG(S)-PON, and NG-PON2. The next generations of ITU PON standards are 50G-PON and 100G-PON. At the same time, the international organization IEEE is developing its PON standards: EPON, 10G-EPON, 25G-EPON, etc.

The architecture of the PON system consists of three segments. The OLT (Optical Line Terminal) is the main element of the system that enables the connection of ONUs to MAN/WAN networks. The next segment is ODN (Optical Distribution Network) - the fiber optic cable plnt. This is the biggest and the most expensive element of this system. The task of the ODN is to connect the ONUs (Optical Network Unit) to the OLT. The final segment is ONU.

There are different FTTx PON scenarios: FTTC (w/DSL), FTTB, FTTH, and FTTR. It depends on the ONU location. FTTH GPON is the most widespread technology, however, due to the great demands of subscribers; today the migration from GPON to XG(S)-PON FTTH is underway or nearing completion.

GPON enables a max 2.5Gbps/1.25 Gbps per PON port. These are enough data rates for most residential users when used with a maximum spit of 32. However, some services such as business applications and consumer online gaming, AR/VR, telemedicine, 3D web scenes, holo chat applications, 4K and 8K video, free viewpoint, etc. require higher data rates in both directions. That is why the standards for migration from GPON to XGPON or XGS-PON started.

XG(S)-PON enables higher data rates and lower latency compared to GPON. Max data rates per PON port is 10/2.5 Gbps (XG-PON) or 10/10 Gbps (XGS-PON). This standard is intended for all residential users and small and medium enterprises. There are several different 10G PON technologies (10G EPON, XG-PON, and XGS-PON), but telecommunications operators generally use XGS-PON. A small of number telecommunications operators introduced NG-PON2 or 25G-PON due to the demands of large enterprises (large companies, factories, and 5G mobile operators). 100G PONs are also in development.

Migration from GPON to XG(S)-PON

Telecommunications operators want an easy and safe migration to the new PON standard. They want to save the most expensive part of the system - the cable plant, ODN. GPON and XG(S)-PON use different wavelengths, which enables the coexistence of two PON standards in the same ODN. GPON uses 1490 nm for downstream and 1310 nm for upstream, and XG(S)-PON uses 1577 nm for downstream and 1270 nm for upstream.

GPON Wavelengths

Modern OLTs generally support GPON and XG(S)-PON boards. Because of that, migration from GPON to XG(S)-PON can be realized using XG(S)-PON service boards (hybrid solution) or combo/flex PON service boards.

Hybrid solution

A hybrid solution is a solution where GPON and XG(S)-PON service boards are combined in the same OLT or in two or more independent OLTs. The parallel operation of two PON standards in the same ODN is enabled by using the WDM module (mux/demux). In this way, subscribers can use GPON or XG(S)-PON.

GPON hybrid 1+10GPON
This solution maintains the existing GPON boards, however, this solution also introduces new component - WDM mux/demux. These WDM modules require reorganization in headends (HE) or central offices (CO). In addition, WDM modules increase IL (Insertion Loss) by about 1 to 1.5 dB. Sometimes updating the OLT software or replacing the control boards is required.

Combo or flex PON boards

The second and last solution is the solution with combo or flex PON boards with both GPON and 10GPON on the board with one port. These boards are installed in the existing OLT. This means that the existing GPON service boards are uninstalled. Combo or flex boards have slots for SFP optical modules that combine GPON and XG(S)-PON, and have built-in WDM mux/demux.

Combon 1+10GPON
This solution does not introduce new elements and does not require reorganization in HE or CO. Very rarely, updating the OLT software or replacing the control boards is required. The main disadvantage of this solution is the uninstallation of existing GPON boards.

Future development

The next steps are the mass introduction of 25G-PON, and the testing of 50G-PON. The main drivers of PON development are large enterprises, factories, and 5G/6G mobile operators. Large telecommunications operators in the USA and Europe use NG-PON2 and 25G-PON. The 50G-PON standard is still in the testing phase. Commercial use of this PON standard is still a distant future.

Vladimir Grozdanovic is a graduate electrical engineer for telecommunications with more than 10 years of experience in access networks (HFC and FTTH) in large cable operators in Serbia (SBB and Jotel).

Technical Information on FTTX  From The FOA Online Guide
FTTH Introduction  
FTTH Architectures
FTTH in MDUs (Multiple Dwelling Units)  
FTTH PON Standards, Specifications and Protocols  
FTTH Design    
FTTH Installation 
FTTH Customer Premises Installation  
FTTH Network Testing  
FTTH Case Studies: Do-It-Yourself FTTH  
FTTH Project Management
Migration from GPON to XG(S)-PON  
Migration from CATV HFC To PON  

The Fiber Optic Association Fiber To The Home Handbook: For Planners, Managers, Designers, Installers And Operators Of FTTH - Fiber To The Home - Networks
FOA FTTH Handbook
The Fiber Optic Association Fiber To The Home Handbook
Available in paperback or as an eBook on the Amazon Kindle  Available direct from, local booksellers and other distributors.

Training & Certification
Fiber U Online FTTx Self Study Program (free)

FOA Certification Overview
FOA FTTx Certification Requirements
FOA-Approved Training Programs

 Table of Contents: The FOA Reference Guide To Fiber Optics


(C)2021, The Fiber Optic Association, Inc.