EPON Network

Ethernet Passive Optical Network (EPON)

What is EPON?

EPON stands for Ethernet-based Passive Optical Network, it is a new hotspot for broadband access developed after ATM Passive Optical Network (APON), and one of the efficient access solutions to solve the bottleneck problem of broadband access. Broadband access not only requires the ability to provide high-speed Internet access services, but also needs to be able to provide multiple services and meet its QoS, and the price can be affordable. EPON, which utilizes the existing fiber optic network of cable TV through wavelength division multiplexing architecture, is such a cost-effective broadband access solution.

A typical EPON system consists of three parts: OLT (Optical Line Terminal), ONU (Optical Network Unit), and POS (Passive Splitter). The OLT is placed in the central computer room, and the ONU is placed near or integrated with the network interface unit. POS is a passive device that connects OLT and multiple ONUs. In the EPON system, OLT is a switch or router that provides an interface to the metropolitan area network (WAN) upwards and an interface to connect to the PON downwards. In order to support IP, ATM, FR, and even traditional TDM voice services and T1/E1 services, OLT can provide Gigabit Ethernet interface, ATM interface, SDH/SONET, and even WDM interface, respectively. OLT not only has the functions of network centralization and access, but also supports bandwidth allocation, QoS/SLA, network security, and other functions.


ONU receives optical signals from OLT and provides various application interfaces (such as 10/100 Mbit/s Ethernet interface) downwards to support data, voice, and video services. It is also responsible for transmitting uplink data to OLT. In addition, ONU also provides switching functionality for Ethernet Layer 2 and Layer 3, enabling internal routing selection. POS is a simple passive device used to connect OLT and multiple ONUs, and for optical power distribution. It does not require power and can be placed in an all-weather environment. A typical POS has a branching rate of 8, 16, or 32, and can be connected at multiple levels. In a 1:16 or even 1:32 EPON system, the design distance between OLT and all ONUs can reach a maximum of 10 km (or even 20 km, depending on product performance and network structure).


EPON uses a wavelength division multiplexing technology combining 1550 nm downstream and 1310 nm upstream on a single fiber, transmitting data in a point-to-point manner. In an EPON system, downlink data is transmitted to each ONU through broadcast, where the ONU only receives packets with the destination MAC address as its own address and switches them down to each port. The data transmission in the uplink direction adopts time division multiplexing technology, where each ONU sends data in sequence within the time slot allocated to it by the OLT, and the data in the POS is uniformly transmitted to the OLT. In order to avoid collisions and achieve signal synchronization, automatic ranging should be implemented between OLT and ONU, and bandwidth and time slot allocation should be based on the Service Level Agreement (SLA) of each user.

What are the advantages of EPON?

EPON adopts a point-to-point structure and passive fiber optic transmission method, providing multiple services over Ethernet. EPON technology integrates low-cost, high bandwidth Ethernet devices and low-cost fiber optic network technology, and has unique advantages compared to other access technologies, mainly reflected in the following four aspects:


Good compatibility

EPON adopts Ethernet technology, which is the most successful and mature LAN technology to date, and can be said to be the mainstream of user LAN technology. Due to EPON being only based on the existing IEEE 802.3 protocol, with minor modifications and additions, it is basically compatible with Ethernet technology for transmitting Ethernet frames in user access networks. Using Ethernet as the access network not only has low cost, but also good universality, avoiding complex transmission protocols and format conversion, high efficiency, and simple management.


Low construction and maintenance costs

The EPON system significantly reduces the number of optical fibers, optical transceiver modules, and central office equipment. Due to the continuous decrease in the cost of optoelectronic devices, the cost of each line of equipment in EPON can be compared to ADSL and CM, especially with the current lower price of fiber optics compared to cables. These conditions have become the foundation for the development of FTTH. Meanwhile, the foundation of EPON is Ethernet, and the related components and equipment of Ethernet have the lowest prices. Using EPON as an access network has low cost, good universality, eliminates the protocol and format conversion of IP data transmission, high efficiency, and simple management. In addition, there are only passive optical devices such as optical fibers and splitters between the office end (OLT) and the user (ONU), which do not require renting a computer room, equipping power supplies, or active equipment maintenance personnel. Therefore, it can effectively save operation and maintenance costs.


High bandwidth

The current downlink transmission rate that EPON can provide is 1 25 Gb/s, with a single wavelength uplink rate of 125Mb/s, and can be upgraded to 1GB/s with the development of Ethernet technology. This is much higher than the current access methods and can meet the bandwidth requirements of various businesses such as broadband internet access, video on demand, online games, video calls, digital high-definition televisions, etc. It fully meets the bandwidth needs of access network customers and can conveniently and flexibly dynamically allocate bandwidth according to changes in user requirements, making it the ultimate access method for users.


High reliability of access

Fiber optic has low loss, wide bandwidth, and a transmission distance of up to 20 km, avoiding the distance bottleneck problem of traditional transmission media (such as twisted pair, Category 5 lines, cables, etc.); The entire optical transmission channel consists of optical fibers and passive optical devices, which can effectively avoid electromagnetic interference and lightning effects, ensuring the quality of signal transmission; Adopting passive fiber optic line design with fewer fault points, replacing copper cables with optical cables can also solve the problem of overcrowding in urban underground communication pipelines.

EPON Applications

Broadband access has gradually become a new business growth point in the telecommunications industry. Due to its good compatibility with Ethernet, high bandwidth, long transmission distance, no active devices between devices, and low cost, EPON can be used as a good broadband access method. According to different user needs, EPON can have the following application modes [2]:


Fiber to the roadside mode (FTTCab)

The passive splitter is located outdoors, and the ONU is located on the roadside. This mode is mainly applied to ordinary residential communities. A set of OLT can cover a large number of users, and use layer 2 switches or VDSL devices to share bandwidth under the ONU, thereby reducing the access cost for each user. Because the EPON system can be smoothly upgraded, it is conducive to deploying nodes according to the actual needs of users, thereby protecting the initial investment of operators.


Fiber to the building mode (FTTB)

The passive splitter is located outdoors, and the ONU is located inside the building. In some high-end office buildings where it is inconvenient to lay out network cables, EPON+VDSL systems can be used to provide customers with broadband access and PSTN services through ONU+VDSL equipment and existing telephone lines in the building.


Fiber to the floor mode

The passive splitter is located inside the building, and the ONU is located on the floor. This method can generally be used in high-end office buildings to provide reliable and high-speed broadband access for business users in commercial buildings. OLT can be placed in a central computer room, using a star shaped network structure and extending to multiple nearby buildings. Bandwidth can be directly allocated to multiple user terminals through the ONU, or a second layer Ethernet switch can be used to form a local area network under the ONU. To ensure the data security of commercial users, different VLANs can be set for them. In response to the high demand for service quality from commercial users, high priority and high bandwidth can be set to ensure that users still have a certain level of QoS guarantee when the system is busy.


Fiber to the Desktop Mode (FTTD)

The passive splitter is located inside the building, and the ONU is located on each user’s desktop. This mode is mainly used for high-end villas and residential areas to achieve Fiber to Home (FTTH), and users can enjoy 100 Mbit/s bandwidth access to the Internet. OLT can be placed in a central computer room, with a star shaped network structure extending to nearby high-end villas and communities, and ONU directly placed in the user’s home. This application mode requires the functionality of the ONU to be as simple as possible, providing users with 10/100 Mbit/s Ethernet access is sufficient. Considering the increasingly fierce competition in the real estate industry in some regions, fiber to the home can enhance the value of real estate and have advertising effects, so real estate developers may also share equipment investment.


In the above modes, the bandwidth available to users ranges from low to high, and the required cost also ranges from low to high. Operators can mix multiple modes according to the specific needs of users. EPON can also effectively solve the problems faced in the construction of ADSL and LAN access, in order to achieve sustainable development of broadband access. Compared with point-to-point structures, EPON systems can save optoelectronic converters and a large amount of optical fibers, thus having significant overall cost advantages. If EPON is combined with existing broadband technologies such as ADSL, LAN, VDSL, etc., the cost advantage of EPON can be fully utilized, thereby improving the coverage of broadband access in a more economical way. The only way to further develop ADSL in areas limited by output rates is to move down the DSLAM node. However, using other methods to move down will consume a significant amount of access network fiber optic cable resources. If EPON technology is used to move DSLAM down, it will greatly save on backbone optical cables. LAN access is mainly used for the construction of information technology communities (buildings). The LAN access structure requires Ethernet switches to be installed at the access layer of the metropolitan area network, the central data center of the park, buildings, and even floors, resulting in high equipment costs, complex management, and low installation rates. By adopting EPON technology, ONUs can be installed only in buildings or floors as needed, with passive splitters used throughout the middle, greatly reducing active equipment. It has the advantages of fewer types of equipment, flexible networking, and convenient management, which is also conducive to improving the actual installation rate of equipment.


Finally, using EPON technology can achieve FTTH in stages. In the initial stage of broadband access services, EPON combined with ADSL and VDSL technologies can achieve full coverage of ADSL and VDSL in the shortest possible time, meeting the simple broadband needs of ordinary users for high-speed internet access. It can also economically use ONU to directly connect commercial users to the broadband network, achieving FTTB and FTTO. With the maturity of 10 Gbit/s Ethernet technology, when device costs decrease and user demand for FTTH is strong, gigabit EPON systems can upgrade to 10 Gbit/s or increase bandwidth several times through wavelength division multiplexing, and smoothly transition to FTTH through EPON cascading.

What is the difference between Epon and Gpon?

GPON and EPON have different application ranges and overlapping application scenarios. Looking ahead to the future broadband access market, it may not be anyone who replaces each other, but rather coexistence and complementarity. For customers with high requirements for bandwidth, multi service, QoS and security, as well as ATM technology as the backbone network, GPON will be more suitable; For customer groups that are cost sensitive, have low requirements for QoS and security, EPON becomes the dominant player.


There will be overlap in the application of FTTB for residential users, which can meet the needs of broadband acceleration applications; In FTTH application scenarios, especially in full business operation scenarios, GPON has more advantages (higher bandwidth capacity: 2 00 times the downlink bandwidth of EPON and 1.37 times the uplink bandwidth of EPON; Higher spectral ratio (1:128) and lower networking cost compared to EPON.


In fact, there is not much difference in the construction mode between GPON and EPON during the process of network construction and networking, it is just a technological choice faced by operators in broadband access. From the current perspective, GPON’s business improvement capability is basically consistent with EPON, and there is currently no business access that GPON can do but EPON cannot.


Due to different technical characteristics, EPON and GPON technologies are actually two different market applications. EPON technology is more suitable for the application type of Internet access, and GPON technology is more suitable for the application type of full service operation and three networks integration. From a business perspective, these are actually two segmented markets. However, from the perspective of end users, whether it is EPON or GPON, they are actually invisible to users, especially in the FTTB construction model. Users only see Ethernet interfaces and telephone interfaces in their home terminal devices, and there is no need to consider GPON and EPON.