XG-PON and XGS-PON both belong to the GPON series, and XGS-PON is the technical evolution of XG-PON from the technical roadmap.

In ECOC 2023, C-light OLT and ONU optical modules for telecommunications operations and other fields were demonstrated on site.

XG-PON and XGS-PON are both 10G PON, the main difference is: XG-PON is an asymmetric PON, and the up-and-down speed of the PON port is 2.5G/10G; XGS-PON is a symmetric PON, and the up/down speed of the PON port is 10G/10G.

The main PON technologies in use today are GPON and XG-PON, both of which are asymmetric PON. As the user's uplink/downlink data is generally asymmetric, taking a first-tier city as an example, in the uplink traffic of OLT, the average uplink traffic is only 22% of the downlink traffic, so the technical characteristics of asymmetric PON are basically matched with the user's needs. More importantly, the uplink rate of asymmetric PON is lower, the cost of sending components such as lasers in ONU is lower, and the device price is correspondingly lower.

However, the needs of users are diverse, with the rise of live broadcast, video surveillance and other services, users are more and more concerned about the upstream bandwidth of the scene, and the call line needs to provide up/down symmetrical circuits. These businesses are driving the demand for XGS-PON.

Coexistence of XGS-PON with XG-PON and GPON

XGS-PON is a technical evolution of GPON and XG-PON, and supports the hybrid access of GPON, XG-PON, and XGS-PON ONUs.

1  Coexistence of XGS-PON and XG-PON

Like XG-PON, XGS-PON uses broadcast for downlink and TDMA for uplink.

Since XGS-PON and XG-PON have the same downlink wavelength and downlink rate, the downlink of XGS-PON does not distinguish between XGS-PON ONUs and XG-PON ONUs, and the optical splitters broadcast the downlink optical signal to each XG(S)-PON (XG-PON and XGS-PON) ONUs in the same ODN link. Each ONU chooses to receive its own signal and discard the other signals.

The uplink of the XGS-PON transmits data according to the time slot, and the ONU sends data within the time slot permitted by the OLT. OLT depends on the traffic requirements of the ONU and the type of ONU (is it XG-PON or XGS-PON?). Allocate time slots dynamically. In the time slot assigned to the XG-PON ONU, the data transmission rate is 2.5Gbps; In the time slot assigned to the XGS-PON ONU, the data transfer rate is 10Gbps.

It can be seen that XGS-PON naturally supports hybrid access with both XG-PON and XGS-PON ONUs.

2  Coexistence of XGS-PON and GPON

XGS-PON uses a Combo scheme to share ODN with GPON because the up-downlink wavelength is different from GPON's. For details about the principles of the Combo solution, see Discussion on Improving Resource Utilization of the Combo User Board XG-PON.

The XGS-PON Combo optical module integrates the GPON optical module, XGS-PON optical module, and WDM wave synthesiser.

In the uplink direction, after the optical signal enters the XGS-PON Combo port, the WDM filters the GPON signal and XGS-PON signal according to the wavelength, and then sends the signal to different channels.

In the downlink direction, the signals from GPON channel and XGS-PON channel are multiplexed through WDM, and the mixed signals are downlink to ONU through ODN. Because the wavelength is different, different types of ONU receive the signal by selecting the wavelength they need through the internal filter.

Since XGS-PON naturally supports coexistence with XG-PON, the XGS-PON Combo solution supports the mixed access of GPON, XG-PON, and XGS-PON ONUs. The XGS-PON Combo optical module is also called a three-mode Combo optical module. The XG-PON Combo optical module is called a two-mode Combo optical module because it supports the mixed access of GPON and XG-PON ONUs.

Write at the end

Due to the impact of equipment cost and equipment maturity, the current equipment price of XGS-PON is generally much higher than that of XG-PON. Among them, the unit price of OLT (including Combo user board) is about 20% higher, and the unit price of ONU is more than 50% higher.

Although the inbound line needs to provide an up/down symmetrical circuit, the actual traffic of most inbound lines is still dominated by the following lines. Although there are more and more scenarios in which users pay more attention to uplink bandwidth, there are almost no cases in which services cannot be accessed through XG-PON but must be accessed through XGS-PON.

C-light Products for FTTx Broadband, one of the realm the company focused on, were introduced In CIOE 2023

Due to the good compatibility of the XGS-PON Combo solution, the unit price of XGS-PON OLT (including Combo user board) is not much higher than that of XG-PON, and a small number of XGS-PON OLT devices can be deployed in first and second-tier cities and provincial capitals (the upstream traffic of the headquarters of the passenger line is usually higher). The XGS-PON ONU is configured according to the actual uplink bandwidth requirements of users.