What is XGS-PON? How does XGS-PON coexist with GPON and XG-PON?

XGS-PON

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1. What is XGS-PON?

Both XG-PON and XGS-PON belong to the GPON series. From the technical roadmap, XGS-PON is the technological evolution of XG-PON.

Both XG-PON and XGS-PON are 10G PONs. The main difference is: XG-PON is an asymmetric PON, and the uplink/downlink rate of the PON port is 2.5G/10G; XGS-PON is a symmetrical PON, and the uplink/downlink rate of the PON port is 10G/10G.

GPON XG-PON XGS-PON

Technology GPON XG-PON XGS-PON
Technical standard G.984 G.987 G.9807.1
Line rate (Mbps) Downlink 2488 9953 9953
Uplink 1244 2488 9953
Maximum split ratio 128 256 256
Maximum transmission distance (km) 20 40 40
Data packaging GEM XGEM XGEM
Available broadband (Mbps) Downlink 2200 8500 8500
Uplink 1000 2000 8500
Working center wavelength (nm) Downlink 1490 1577
Uplink 1310 1270

The main PON technologies currently used are GPON and XG-PON, both of which are asymmetric PONs. Since the user’s uplink/downlink data is generally asymmetric, taking a city as an example, among the upstream traffic of OLT, the average upstream traffic is only 22% of the downstream traffic. Therefore, the technical characteristics of the asymmetric PON basically match the needs of users. More importantly, the upstream rate of an asymmetric PON is low, the cost of transmitting components such as lasers in the ONU is low, and the equipment price is correspondingly low.

pon

However, the needs of users are diverse. With the rise of services such as live broadcast and video surveillance, there are more and more scenarios where users pay more attention to the upstream bandwidth, while the private line for inbound customers needs to provide symmetrical upstream/downstream circuits. These services promote the demand for XGS-PON.

2. Coexistence of XGS-PON, XG-PON and GPON

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

2.1 Coexistence of XGS-PON and XG-PON

Like XG-PON, the downlink of XGS-PON adopts broadcast mode, and the uplink adopts TDMA mode.

Since the downstream wavelength and downstream rate of XGS-PON and XG-PON are the same, the downstream of XGS-PON does not distinguish between XGS-PON ONU and XG-PON ONU. The optical splitter broadcasts the downlink optical signal to each XG(S)-PON (XG-PON and XGS-PON) ONU in the same ODN link. Each ONU chooses to receive its own signal and discards other signals.

GPON XG-PON XGS-PON-1

The upstream of the XGS-PON transmits data according to the time slot, and the ONU sends the data in the time slot permitted by the OLT. The OLT dynamically allocates time slots according to the traffic requirements of different ONUs and the type of ONUs (either XG-PON or XGS-PON). In the time slot allocated to the XG-PON ONU, the data transmission rate is 2.5Gbps; in the time slot allocated to the XGS-PON ONU, the data transmission rate is 10Gbps.

GPON XG-PON XGS-PON-2

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

2.2 Coexistence of XGS-PON and GPON

Since the uplink/downlink wavelengths are different from GPON, XGS-PON adopts the Combo solution to share ODN with GPON.

The Combo optical module of XGS-PON integrates GPON optical module, XGS-PON optical module and WDM combiner.

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

GPON XG-PON XGS-PON-3

In the downstream direction, the signals from the GPON channel and the XGS-PON channel are multiplexed through WDM, and the mixed signal is downstream to the ONU through the ODN. Due to the different wavelengths, different types of ONUs select the required wavelength through the internal filter to receive the signal.

GPON XG-PON XGS-PON-4

Since XGS-PON supports coexistence with XG-PON, the Combo solution of XGS-PON supports the mixed access of three types of ONUs, namely GPON, XG-PON and XGS-PON. The Combo optical module of XGS-PON is also called 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).

3. At the end

Affected by equipment cost and equipment maturity, currently, the 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 private line needs to provide symmetrical uplink/downlink circuits, the actual traffic of the vast majority of inbound private lines is still dominated by downlinks.  Although there are more and more scenarios where users pay more attention to the upstream bandwidth, there is almost no service that cannot be accessed through XG-PON and must be accessed through XGS-PON.

Due to the good compatibility of the XGS-PON Combo solution, the unit price of the XGS-PON OLT (including the Combo user board) is not much higher than that of the XG-PON, and a small amount can be deployed in large cities (where the upstream traffic of the headquarters of the passenger dedicated line is usually high). XGS-PON OLT equipment and XGS-PON ONU are equipped according to the actual online bandwidth requirements of users.

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