5 Key Facts about PON and the evolution of GPON technology to 10G PON & XGS PON

In our first article on Passive Optical Networking we looked at some of the key foundations of PON, to get an understanding of what Passive Optical Networking (PON) is, how PON works, along with the core key benefits and some definitions of some of the key terms you will come across. We also took a look at the history of PON and where it is headed in the future.

In this article we’ll take a more in-depth look at GPON technology, including the latest 10G PON standards (XG-PON and XGS PON) and NG-PON2. We’ll also look at GPON transceivers, the criteria you need to consider for selection and PLC splitters that do the hard work of splitting fiber connections.

But, first of all a quick reminder of what GPON is…

What is GPON?

Just to recap a little, GPON is used predominantly in FTTH (Fiber to the Home), FTTB (Fiber to the Building) and FTTP (Fiber to Premises) networks. GPON is the standard that enables a single fiber connection, sent from the central office, to be split using fiber optical splitters into multiple fiber connects to serve the needs of multiple end customers. GPON makes more efficient use of the physical fiber network being deployed than point-to-point fiber. Gigabit Passive Optical Networking (GPON) was the first ITU standard enabling 1Gbps communications.

1) ITU PON Transmission Standards – GPON, XG-PON, XGS-PON and NG-PON2

In our first blog we covered the evolution of the ITU PON standards. Here we take a closer look at the specifications for each of the latest standards.

2) GPON vs XG-PON vs XGS-PON vs NG-PON2 – What is the difference?

GPON technology has been the most widely used PON standard in FTTH networks.  The ITU standard has been updated to handle higher transmission speeds, which resulted in the development of XG-PON (in 2010) and XGS-PON (in 2017), which can handle bitrates of up to 10Gbps.

NG-PON2 – In between the development of XG-PON and XGS-PON, NG-PON2 was standardized in 2013.  NG-PON2 uses TWDM (Time and Wavelength Division Multiplexing) to handle both asymmetrical (10Gbps/2.5Gbps) and symmetrical transmission  (10Gbps/10Gbps) over multiple channels and across tunable wavelengths.

XG-PON vs XGS-PON– As mentioned earlier, XG-PON was standardized in 2010 and provides asymmetric bandwidths of 10Gbps downstream and 2.5Gbps upstream. However, XGS-PON is not a development of XG-PON, as its name might suggest, but is an adaptation of TWDM-PON used in NG-PON2 without multi-channels and tunable wavelengths.  Therefore, XGS-PON can provide both asymmetrical transmission at 10G/2.5G or symmetrical transmission at 10G/10G versus XG-PON which is only able to provide asymmetrical 10G/2.5G. 

XGS-PON and NG-PON2 – With enhanced speeds over GPON, both offer the opportunity of advanced services for FTTH, support mission-critical business applications and underpin 5G mobile.  The key difference between XGS-PON and NG-PON2 is the multiple  tunable wavelengths supported by NG-PON2, versus the fixed wavelengths supported by XGS-PON.

3) GPON, XGS-PON and NG-PON2 Wavelengths for Service Flexibility

Because XGS-PON and NG-PON2 were designed to co-exist with GPON, the standards use different wavelengths on the same fiber, which enable different portions of the optical distribution network (ODN) to be used to provide different levels of service for different purposes and applications. For example, service providers are able to increase the bandwidth capacities of existing FTTH GPON networks, reduce deployment costs, enable more customers to share the same fiber and even enable multiple operators to share the same network.

The diagram above shows each Transmission Standard and the wavelength range used, along with the potential upload and download speeds.

4) Selecting the Right PON Transceiver

Transceivers are an essential part of any Passive Optical Network and are needed at both the central optical line terminal (OLT) and subscriber optical network unit (ONU). PON transceivers are specifically designed for use in passive optical networking and use different wavelengths to transmit and receive signals between the OLT and ONU.

When selecting the right PON transceiver there are several selection criteria to consider:

• OLT or ONU – to determine where the transceiver will be used
• Form Factor – different form factors are available depending on the PON standard being used. For example, SFP (Single Form Factor Pluggable), SFP+ (Enhanced Small Form-Factor Pluggable), XFP (10 Gigabit Small Form Factor Pluggable).  The table below shows the form factors for each of the PON standards.
• GPON SFP transceivers are available in two classes – Class B+ and C+. The main differences between the classes being:
  • the amount of power transmission (Tx) and reception (Rx) they can support, along with
  • the number of connections they can support. Class B+ support up to 32 ONUs and Class C+ supports up to 64 end-user ONU connections.

5) Selecting PLC Splitters used in Passive Optical Networks

A PLC splitter (PLC stands for Planar Lightwave Circuit) is the device at the heart of the PON used to split light beams received from the OLT into multiple light beams to be transmitted to ONUs.  The PLC splitter also receives light beams back from multiple ONUs and combines them back into one light beam.  Usually positioned at a central office or at distribution points within the passive optical network. 

Split ratios – GPON technology can typically handle up to a 1:128 split ratio. Newer 10G GPON technologies can handle up to a split ratio of 1:256 (or 2:128). 

Find out more about Pro Optix PLC Splitters >