The History of PON

Many people have questions about the relationship between EPON, GPON, 10G PON, XG-PON, and NG-PON 2. Today, through this article, Yingda will provide a detailed introduction, hoping to help you.

EPON and GPON

Let’s begins with the origin of PON.

In the 1980s, with the rise of computer and multimedia technology, more and more people began to own computers, and also began to contact the network (LAN or Internet). So, data communication services began to rise, and the demand for internet access emerged.

In the early days, the internet services provided by telecom operators were mainly through copper cables such as telephone lines, twisted pair cables (Ethernet cables), and coaxial cables. Technologies include ADSL (Asymmetric Digital User Line) and ISDN dedicated line (Integrated Services Digital Network).

These methods either have slow speeds or high costs, and cannot meet the needs of users. So, OPTICAL FIBER, as a new type of communication medium, began to enter people’s field of vision.

Since Mr. Gao Kun, a Chinese scientist, laid the theoretical foundation for fiber optic communication through a paper in 1966, this technology has entered a stage of rapid development. The fiber optic manufacturing process is constantly maturing, and the industry chain is also increasingly taking shape.

In the late 1980s, in order to apply fiber optics to broadband access services, manufacturers gradually introduced their own narrowband PON technology. At that time, the speed of this technology was very low, not exceeding 2Mbps. Moreover, because manufacturers are fighting on their own, there has never been a unified standard and specification.

In 1995, seven network operators including BELLSOOTH, BT, and France Telecom jointly initiated the establishment of the Full Service Access Network Alliance (FSAN), hoping to propose a unified optical access network equipment standard.

Not long after, in 1997, based on the recommendations of FSAN, ITU-T (International Telecommunication Union Telecommunication Standardization Branch) launched the APON technology system, also known as the G.983.1 standard.

APON is ATM PON. ATM is not an automatic teller machine, it stands for Asynchronous Transfer Mode. The essence of ATM is a transmission protocol. The older generation of communicators must be familiar with ATM, which was once a competitor to IP protocol and was very popular.

In 2001, FSAN and ITU-T upgraded and revised the APON specification, and renamed it BPON (Broadband PON, Broadband Passive Optical Network). The main reason for the name change is that they do not want APON to be misunderstood as only providing ATM services.

In order to further improve the speed standards of PON, FSAN launched a new project in 2002 to standardize PON networks above 1Gbps.

In March 2003, based on the recommendations of FSAN, ITU-T issued the G.984 standard, also known as GPON (Gigabit portable PON).

While FSAN and ITU-T are thriving, another standardization organization is also busy tinkering with PON technology. It is the equally renowned IEEE (Institute of Electrical and Electronics Engineers).

IEEE is the creator and major supporter of the Ethernet standard.

After IEEE released the Gigabit Ethernet standard in 1998, it sought to develop an Ethernet based PON standard.

In 2000, IEEE established the EFM Working Group and officially launched related standardization work. The full name of the EFM working group is interesting, called the Ethernet for the First Mile, belonging to the IEEE 802.3 group that developed Ethernet standards.

In April 2004, the EFM working group achieved great success and officially launched the IEEE 802.3ah standard, also known as EPON (Ethernet PON) based on Ethernet.

Over time, ATM gradually lost its position and declined in competition with IP. APON (BPON) has also been abandoned by operators and withdrawn from the historical stage due to cost, efficiency, and other reasons.

The following focuses on EPON and GPON, which had already become mainstream in the industry at that time.

EPON and GPON are different technology systems introduced by different standard organizations. There is no upgrading, evolution or substitution relationship between the two, which can be considered as parallel development.

The key difference between EPON and GPON lies in the second layer (i.e. data link layer):

EPON, On the second layer, is to replace ATM with Ethernet;

GPON adopts a newly defined encapsulation structure GEM (GPON Encapsulation Mode) in the second layer, which encapsulates and maps various services such as Ethernet, TDM, ATM, etc.

Let’s make a simple comparison through the following table:

In short, EPON and GPON each have their own advantages and disadvantages. Simply put, GPON has a larger bandwidth, more users, and higher efficiency, but it is also more complex to implement, resulting in higher costs.

From the perspective of domestic market share, EPON was widely adopted by China Telecom at that time, while GPON was more popular among China Unicom and China Mobile.

10G-EPON and XGS-PON

EPON and GPON are both PON at the 1Gbps level. Note that this 1Gbps is not the speed on the user side. EPON and GPON can only provide users with a speed of 100Mbps.

Obviously, with the development of the times, this rate cannot meet the needs of both household and business users. So PON began to evolve towards the 10Gbps level.

In 2006, IEEE initiated the development of a 10Gbit/s EPON system standard, which later became IEEE 802.3av, 10G-EPON.

In this standard, 10G EPON is divided into two types: one is asymmetric mode, with a downlink rate of 10 Gbps and an uplink rate of 1 Gbps; The other is a symmetrical approach, where both uplink and downlink rates are 10 Gbps.

The GPON of ITU-T is also evolving.

In 2008, ITU initiated research on the next generation GPON standard. In 2010, the XG-PON standard was born, which is the ITU-T G.987 series.

At the beginning, XG-PON also had two ways, one was asymmetric XG-PON1, with a downlink rate of 10 Gbps and an uplink rate of 2.5 Gbps; Another method is the symmetrical XG-PON2, with both uplink and downlink speeds of 10 Gbps.

Later, around 2013, it was suggested to cancel the XG-PON2 symmetric scheme because it was difficult to implement. XG-PON1 was directly renamed as XG-PON.

Later in 2015, the symmetric scheme was restarted with a new name, XGS-PON (S stands for symmetric).

In 2017, ITU officially adopted the G.9807 XGS-PON international standard.

By looking at the following picture, you should see it more clearly:

Another Combo PON worth mentioning is that the operator has also conducted centralized procurement.

Combo PON is a three in one optical module that integrates GPON optical module, 10G PON optical module, and WDM1r multiplexer internally. In this way, whether the user side is connected to GPON ONT or 10G PON ONT, it can work normally, which is conducive to the upgrade transition.

After 2010, Internet applications such as video and games have developed rapidly, and users have a strong demand for network bandwidth. This further stimulates the maturity of the 10G PON industry chain.

Since 2013, domestic operators have carried out large-scale centralized procurement and batch deployment of 10G PON. In recent years, with the promotion and popularization of “gigabit broadband”, the centralized procurement of 10G PON has reached its peak.

There are also some differences in the upgrade strategies of domestic operators for 10G PON. Mainly China Telecom. Due to the large stock of EPON in the past, Telecom inevitably adopted the 10G EPON solution for upgrading and replacement, but the newly built ones have basically switched to GPON.

From a technical perspective, upgrading and replacing 10G PON is actually very convenient, as it can be directly upgraded on the basis of existing hardware architecture.

Among the three major parts of OLT, ODN, and ONU, ODN (Optical Distribution Network) is almost completely unchanged, anyway it is also passive, just a pipeline, and it is estimated to have no problem for decades. For the OLT equipment in the central office, the original GPON/EPON platform can remain unchanged, and only the high-capacity interface board needs to be upgraded and replaced. User side ONU replacement is relatively simple, and can be gradually phased out and replaced according to user needs (when changing broadband packages).

The Future of PON

For standard organizations, 10G PON is not the end of PON technology, and 25G/50G/100G PON has already been put on the agenda.

Let’s take a look at FSAN and ITU-T first.

After the completion of the XG-PON standard, FSAN initiated research on the NG-PON2 standard (NG-PON1 is the previous 10G PON, including 10G GPON and 10G EPON). The key requirements of NG-PON 2 are mainly 40G downlink and 40G/10G uplink, achieving a transmission distance of 20km and 1:64 splitting.

At that time, the mainstream alternative technology solutions for NG-PON 2 included high-speed TDMA-PON, TWDM PON, OFDM-PON, and WDM-PON. After analysis and comparison, in April 2012, FSAN decided to adopt TWDM PON technology as the implementation solution for NG-PON 2 and initiated the development of the G.989. x series standards, which were finally completed in 2015.

TWDM PON adopts a 4/8 wavelength superposition method, with a single wavelength of 10G TDM.

Let’s take a look at IEEE again.

In 2013, IEEE initiated research on NG-EPON and established IEEE ICCOM to analyze market demand and technical solutions for NG-EPON. In March 2015, IEEE released a white paper on NG-EPON technology. In July 2015, the development of the 100G-EPON standard was initiated and named IEEE 802.3ca. According to the latest information, it may be released in August 2020.

Also below picture for better understanding:

On the basis of 10G TDM, ITU-T experts are also considering further enhancing single wave capacity, with a focus on 25G, 50G, and 100G.

Among them, the difference between 25G and 10G is too small, while 100G is too difficult. So, 50G is generally considered a more suitable direction for evolution.

In February 2018, the domestic optical access network industry successfully promoted the establishment of the 50G TDM-PON standard, marking a crucial step for ITU-T in the research field of next-generation PON standards and further clarifying the future technological evolution path of PON (at least in China).

However, IEEE has not accepted the proposal for a single wave 50G PON. They have significant differences with ITU-T in choosing the next generation PON technology roadmap and cannot reach a consensus in the short term.

In summary, 10G PON can provide 100M~1G bandwidth per user, while 25G/50G/100G PON can provide 1G~10Gbps bandwidth for users. The large-scale deployment of broadband access platforms usually takes about 7-8 years to complete. From 2016 to 2018, we entered the period of large-scale deployment of 10G PON.

That is to say, it is expected that by 2025, we will usher in the large-scale deployment of 5Gbps and 10Gbps fiber optic access broadband.

Fusion of PON Schools

In addition to researching next-generation PON technology, the industry is also closely monitoring an important issue, which is the integration of the ITU-T and IEEE technology schools.

Since the birth of EPON and GPON, the two factions have coexisted for a long time, which is actually very unfavorable for the industry.

On the one hand, it brings difficulties to the technical decision-making of operators and equipment (multiple-choice questions are difficult to solve), and on the other hand, it also increases the cost of the industrial chain (industrial chain enterprises need to invest in two lines).

For the huge optical access network market in China, the impact of the differentiation of PON technology factions is even greater, and there is also more waste of resources. So, Chinese operators and industry chains have a strong desire for PON integration and have done a lot of promotion work.

Under the active promotion of the domestic and international industry, ITU-T and IEEE have also made some positive “gestures”, including issuing joint statements, forming working groups, and establishing contact letter mechanisms. However, to truly achieve the ultimate integration, it still takes a long time at present.