What Is PON?

Passive Optical Network (PON) is a point-to-multipoint optical access technology. It uses only optical fibers to transmit data, voice, and video services.
A PON network consists exclusively of passive optical components. This prevents electromagnetic interference from external devices and lightning strikes, reduces the failure rate of lines and external devices, and simplifies power supply configuration and network management. It also improves system reliability and reduces maintenance costs. Theoretically, a PON network can transmit signals of any format, at any rate.

Contents

How Does PON Work?

On the network shown in the following figure, a PON network consists of the optical line terminal (OLT), optical distribution network (ODN), and optical network unit (ONU).

The OLT is an aggregation device that terminates PON protocol packets at the central office (CO).
The ODN is a passive device that connects the OLT and ONU. It distributes downstream data and centralizes upstream data, and is highly reliable.
The ONU is a user-side terminal that provides various interfaces for users.

PON network components

Downstream and Upstream Data Transmission on a PON Interface

On a PON network, the downstream direction refers to data transmission from an OLT to an ONU, and the upstream direction refers to data transmission from an ONU to an OLT. The following describes the principles of downstream and upstream data transmission:

Downstream: An OLT broadcasts IP data, voice, and video services to all ONUs through a 1:N passive optical splitter (POS). When an ONU receives a data frame, it checks the logical identifier of the data frame at the physical layer. If the logical identifier is the same as that allocated by the OLT, the ONU accepts the data frame; otherwise, the ONU discards the data frame.
Upstream: A 1:N POS uses the time division multiple access (TDMA) function to couple the signals of various services from multiple ONUs to one optical fiber, and sends the signals to the OLT. Signals of different services do not interfere with each other during transmission.

AR routers are typically deployed as ONUs. Therefore, PON interfaces on AR routers are also called PON uplink interfaces.

GPON vs. EPON

Gigabit passive optical network (GPON) is a PON technology standardized by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) in the G.984.x series Recommendations. GPON provides powerful operations, administration, and maintenance (OAM) functions, and has advantages in high rate and multi-service support.

Ethernet passive optical network (EPON) is also a PON technology. It was proposed by the Ethernet in the First Mile (EFM) workgroup established in November 2000, and standardized in the Institute of Electrical and Electronics Engineers (IEEE) 802.3ah. EPON technology complies with IEEE Ethernet standards, and is a good choice for transitioning to an all-IP network.

Table 1-1 GPON vs. EPON

Item	GPON	EPON
Standard	ITU-T G.984.x series	IEEE 802.3ah
Downlink rate	1.25 Gbit/s, 2.5 Gbit/s	1.25 Gbit/s
Uplink rate	155 Mbit/s, 622 Mbit/s, 1.25 Gbit/s, 2.5 Gbit/s	1.25 Gbit/s
Split ratio	Depending on the optical power budget	Depending on the optical power budget
Maximum transmission distance	20 km	10 km/20 km
Data link layer protocol	GEM	Ethernet
Encapsulation efficiency	Higher	High
Costs	High	Low
Typical applications	Best suited for business users and enterprise-level applications that require high bandwidth, high reliability, and multi-service support.	Best suited for small enterprises and families with limited budgets and technical capabilities and providing cost-effective solutions.

PON Application Scenarios

Network access of homes and small enterprises
PON has been widely used in network access of homes and small enterprises to provide high-speed and high-quality broadband services. It ensures a smooth user experience for various high-bandwidth and high-quality network applications, such as web browsing, online video, and cloud gaming.
Network access of businesses and enterprises
PON is also suitable for network access of businesses and enterprises. It provides high-speed and high-bandwidth network connections to meet the requirements of services such as video conferencing, remote office, and data backup.
Network access of industrial and logistics sectors
In the industrial and logistics sectors, PON ensures high-speed and stable network connections, and supports applications such as remote monitoring and remote control.
Network access of education and healthcare sectors
In the education and healthcare sectors, PON provides high-speed and secure network connections to support online education and telemedicine services.
Network access in cities
PON is applicable to urban network access, providing high-speed and high-bandwidth network connections to support various applications of smart cities. Examples include smart transportation, smart security, and smart environment protection.
Network access in rural areas
PON also provides high-speed and stable network connections in rural areas. It supports services such as rural e-commerce, telemedicine, and online education, helping promote digitalization and informatization in rural areas.

PON Technology Evolution

PON technology is evolving as digitalization requirements increase. The following figure shows the PON technology evolution roadmap.

PON technology evolution roadmap

PON Technology Evolution Under ITU-T Standards

The ITU-T is the Telecommunication Standardization Sector of the ITU, and is responsible for establishing global communication technology standards. In the field of PON technology, the ITU-T defines GPON and its subsequent evolution versions through the G.98x series standards.

XG(S)-PON, also known as 10G-PON, is the next-generation GPON technology. It includes XG-PON and XGS-PON. XG-PON provides asymmetric transmission rates (10 Gbit/s downstream and 2.5 Gbit/s upstream), while XGS-PON provides symmetric transmission rates (10 Gbit/s upstream and downstream).
50G-PON is a next-generation PON technology promoted by the ITU-T. It is designed to meet the requirements for high-bandwidth, low-latency, and large-scale connections in the future. Compared with 10G-PON, 50G-PON will increase the bandwidth by five times, provide a cutting-edge service experience, and create more new applications and services. Its typical application requirements will be in smart homes, the digital transformation of industries, and digital city infrastructure in the 10G era.

PON Technology Evolution Under IEEE Standards

The IEEE, also known as the Institute of Electrical and Electronics Engineers, is responsible for developing Ethernet standards. In the field of PON technology, the IEEE defines EPON and its subsequent evolution versions through the 802.3 series standards.

10G-EPON is the next-generation EPON technology. 10G-EPON provides symmetric upstream and downstream rates of 10 Gbit/s, which are higher than those of traditional EPON.
Next-generation EPON (NG-EPON) is promoted by the IEEE to further improve the performance of EPON and 10G-EPON. NG-EPON can implement 25/50G-EPON to meet future network requirements for high bandwidth and low latency.

References

1PON Interface Configuration (NetEngine AR Routers)

2NetEngine AR5700, AR6700, and AR8000 Hardware Description

3NetEngine AR600, AR6100, AR6200, and AR6300 Hardware Description

4ITU-T Standards