Comparing EPON and GPON Technologies: A Comprehensive Analysis

Fiber is seeing wide adoption in the access network to expand capacity and versatility. With PON (Passive Optical Network ) technology gaining popularity and FTTH (Fiber to the Home) networks becoming the trend of future access network, two point-to-multipoint (P2MP) standards - Ethernet passive optical networking (EPON) and GPON (Gigabit Passive Optical Network) are both in active deployment. They are competitive and complementary with their own unique advantages. This tutorial will illustrate the EPON vs GPON comparison from different aspects.

PON Technology

A PON is a fiber network that only uses fiber and passive components like splitters and combiners rather than active components like amplifiers, repeaters, or shaping circuits. Such networks cost significantly less than those using active components. Passive Optical Network (PON) technology is a high-speed, cost-effective fiber-optic communication system designed for broadband access networks. PONs enable the efficient distribution of data, voice, and video services by using passive optical components, eliminating the need for active electronic devices in the network infrastructure.

In a PON, a single optical fiber is shared among multiple end-users through the use of passive splitters, reducing the amount of fiber and equipment needed. This technology is characterized by its simplicity, reliability, and scalability.

PON technology has evolved over the years, with various standards such as BPON (Broadband PON), EPON (Ethernet PON), and GPON (Gigabit PON), providing different levels of performance and capabilities. PONs play a crucial role in delivering reliable and high-speed broadband access to homes, businesses, and other end-users.

Introduction to EPON and GPON

EPON (Ethernet Passive Optical Network) and GPON (Gigabit Passive Optical Network) are variations of Passive Optical Network (PON) technology. A typical PON system includes an Optical Line Terminal (OLT) located at the service provider's Central Office (CO) and numerous Optical Network Units (ONUs) positioned near end-users. Optical splitters are employed to enable a single optical fiber to serve multiple premises.

While EPON and GPON share general concepts and architectures such as PON operation, Optical Distribution Network (ODN) framework, wavelength plan, and application scenarios, their operational mechanisms, data protocols, as well as the features and services they support, differ significantly.

Comparison between EPON and GPON

With their distinct advantages and drawbacks, EPON and GPON are complementary technologies that also compete against each other in certain aspects. In the following sections, we aim to provide a comprehensive comparison between EPON and GPON, shedding light on their respective strengths and limitations.

Data Rate

EPON is defined by the IEEE 802.3 standard, ratified as 802.3ah-2004 for a base rate of 1.25 Gbps (1.0 Gbps prior to 8B/10B coding), and the IEEE 802.3av standard introduces the 10Gbps variant known as 10G-EPON. Notably, the upstream and downstream data rates of EPON are symmetrical.

In contrast, GPON offers versatility in terms of bit rate options within the same protocol. It supports symmetrical data rates of 622 Mbps, 1.25 Gbps, and asymmetrical rates of 2.5 Gbps downstream and 1.25 Gbps upstream. This flexibility allows users to choose the upstream and downstream data rates according to their specific requirements, making GPON more adaptable than EPON.

Split Ratios

Split ratio refers to the number of users intended to be served by a specific PON, typically ranging from 32, optionally 16, 64, to even 128. This ratio is influenced by the performance of optical transceiver modules, as a larger split ratio significantly increases the cost of these modules and decreases the transmission distance. For instance, with a 1:16 split ratio, the maximum transmitting distance may be 20 km, whereas for a 1:32 ratio, the maximum distance is reduced to 10 km. EPON and GPON share similar characteristics in this regard.

EPON generally supports a minimum split ratio of 32 (i.e., 1:32), with the flexibility to define ratios of 1:64 or 1:128. Providers can tailor the split ratio to match the services and bandwidth they aim to support. In contrast, GPON imposes an upper limit on the split ratio, supporting up to 128 but typically being set at 64. Common split ratios for GPON include 1:32, 1:64, or 1:128. Although GPON offers a variety of split ratios, it does not provide a significant advantage in terms of cost considerations. EPON, on the other hand, can deploy more cost-effective optics at the Optical Network Unit (ONU) due to not requiring a split ratio as high as 128.

Layering & Access Service

The layering model and associated management services in both EPON and GPON are mapped directly over Ethernet or via IP. However, achieving the same in GPON involves two layers of encapsulation. First, Time Division Multiplexing (TDM) and Ethernet frames are wrapped into GTC Encapsulation Method (GEM) frames, which have a format resembling Generic Frame Procedure (GFP) derived from ITU G.7401. Subsequently, both ATM and GEM frames are encapsulated into GTC frames, which are then transported over the PON.

EPON presents a much simpler and more straightforward solution compared to GPON. The inclusion of ATM support and the double encapsulation process in GPON do not offer significant benefits over a pure Ethernet transport scheme. EPON is well-suited for data-only services, providing a native Ethernet solution that leverages the Ethernet protocol. On the other hand, GPON utilizes SONET/SDH and the Generic Framing Protocol (GFP) to transport Ethernet. Therefore, in terms of layering comparison, EPON is considered more straightforward than GPON, while for service support, GPON is preferable, especially for triple-play services.

QoS (Quality of Service)

The Ethernet protocol lacks inherent Quality of Service (QoS) capabilities. As QoS is essential for a viable Passive Optical Network (PON) system, most vendors address this in EPON by utilizing VLAN (Virtual Local Area Network) tags. While this effectively resolves the QoS challenge, it introduces higher costs. The manual provisioning of VLAN tags, as there is no automatic provisioning, further contributes to these elevated costs. In contrast, GPON incorporates integrated QoS handling, making it superior to EPON in terms of QoS. This is particularly advantageous as the QoS implementation in EPON tends to be more costly compared to the integrated QoS features in GPON. 

OAM (Operation Administration and Maintenance)

In GPON, three distinct types of control messages play crucial roles: OMCI (ONT Management and Control Interface), OAM (Operations, Administration, and Maintenance), and PLOAM (Physical Layer OAM). The table below illustrates their respective functions.

On the contrary, EPON employs IEEE 802.3ah OAM messages for provisioning, fault isolation, and performance monitoring. These functions are complemented by SNMP (Simple Network Management Protocol) sets and gets facilitated through IETF (Internet Engineering Task Force) and MIBs (Management Information Bases). Additionally, EPON utilizes MPCP (Multi-Point Control Protocol) GATEs/REPORTs for bandwidth granting, enhancing its control message capabilities.

Practical Solution

The EPON Solution provide high-speed transmission up to 1.25G/1.25G over 20KM, meeting growing bandwidth demands. Ensuring reliability, they support industrial temperatures and offer resistance to lightning and interference. Cost-effective with abundant fiber materials, EPON outperforms copper cables in speed and economic benefits within a 20km range.

While the GPON Solution GPON Solution stands out with its versatile business access capabilities, accommodating E1 circuit, Ethernet, and ATM services for comprehensive voice, data, and video applications. Offering efficient coverage with a 1:128 splitting ratio and a 20 km access layer radius, it combines scalability and easy expansion. Moreover, the network's reliability is underscored by its support for industrial temperatures and airtight TO packaging, making it adaptable to diverse environments, including edge computer rooms. Additionally, the GPON network can seamlessly upgrade to XGS-PON to meet increasing demands for higher bandwidth and faster data rates by replacing equipment.

Summary

Whether it is EPON vs GPON or GPON vs EPON，EPON and GPON each possess their own set of advantages and disadvantages. In terms of performance, GPON outperforms EPON, yet EPON excels in deployment time and cost-effectiveness. Currently, EPON maintains its position as the mainstream technology, with GPON catching up. Looking ahead in the broadband access market, coexistence and complementation seem likely. GPON is an ideal choice for users with demands for multi-service support, high Quality of Service (QoS), security needs, and an ATM backbone network. On the other hand, EPON may be preferable for users prioritizing cost efficiency and having less stringent security requirements.