FTTH Network Basis: GPON vs EPON Technology
Author Aiyden
Date 03/15/2022
In a previous post, we mention that the optical distribution frame (ODF) is one of the components in the optical distribution network (ODN), and ODN is one part of the passive optical network (PON) system. PON is the key technology to realize FTTx and provide point-to-multipoint (P2MP) optical fiber access. Then what is GPON EPON? What are the differences between EPON and GPON? To have a clear picture of the two, let's go further to talk about GPON vs EPON technology in the FTTH network.
What is PON?
PON (Passive Optical Network) is the fundamental technology of FTTx. It is an optical fiber communication network that provides broadband network access to end-users. This passive fiber optic network features splitting the signal without the need for electrical power. It is composed of OLT (Optical line terminal), ONU (optical network unit), and ODN. PON utilizes a P2MP topology. Compared to other optical fiber access network solutions such as point-to-point (P2P) and Fibre to the Curb (FTTC) switch, PON architecture is a win-win solution for cutting transmission costs and lowering the failure rate on the access side.
What is GPON vs EPON?
Both Ethernet Passive Optical Network (EPON) and Gigabit Passive Optical Network (GPON) are variations of PON. They are derivatives of different needs in different times for supplying optical fiber broadband access networks with P2MP topology.
EPON is an Ethernet-based PON technology that complies with IEEE 802.3 standard. IEEE published the initial version in 2004, which adopts PON technology in the physical layer (layer 1) and Ethernet protocol in the data link layer (layer 2), realizing Ethernet access by PON topology and offering multiple services over Ethernet. It combines Ethernet and PON tech in one and inherits the benefits of the two.
Ethernet PON uses WDM (Wavelength Division Multiplexing) technology to achieve bidirectional transmission via a single fiber. Downstream data uses broadband technology while upstream data adopts Time Division Multiplex Access (TDMA) technology.
GPON, a gigabit PON technology, is based at ITU-TG.984.x. It is the latest standard to access broadband passive optical fiber. GPON owns the pros of higher broadband, high efficiency, broad coverage, and user access interface diversity, wherefore carrier-grade users treat it as the optimal solution to bring broadband into access network business and realize a comprehensive transformation.
What is the Difference Between EPON and GPON?
GPON vs EPON — Origin Background
The advent of EPON is to break through the bottleneck of the previous generation PON. Its older brother (BPON) uses ATM as layer 2 technology and can only provide 600Mbit/s bandwidth as the limit. Ethernet PON brings Ethernet to the optical fiber broadband access network, offering two times the speed of Broadband PON. It inherits the advantages of Ethernet's low cost, protocol flexibility, and technology maturity. Hence EPON has a wide range of markets and compatibility.
GPON draws lessons from its two older brothers, develops the BPON triple-play services, makes up for EPON's deficiencies in versatility and capacity. It is targeted at the telecom industry, catering to the needs of multi-service, QoS guaranteed full-service access. It is striving for an optimal, full-service, and most efficient solution.
GPON vs EPON — Bandwidth
In brief, the maximum data rate of GPON is two times the EPON, and the difference lies in downstream speed, dissymmetrical data rate, and multiple rates option.
EPON offers a max downstream data rate of 1.25 Gbit/s, the same as its upstream speed. However, GPON supports three data rate modes options: a data rate in parallel of 622 Mbp/s in upstream and downstream, a data rate in parallel of 1.25Gbit/s in both streams, and a dissymmetrical data rate of 2.488 Gbit/s in downstream and 1.25Gbit/s in upstream. First, three-speed provides a flexible solution for a specific business. Second, GPON offers twice the bandwidth of EPON, bringing an unprecedented high bandwidth to the PON technology - downstream up to 2.488 Gbit/s. Besides, the asymmetric feature makes it more ideal for broadband data service.
GPON vs EPON — Optical Split Ratios
Split ratios specify how many ONUs an OLT can carry. The larger the denominator, the more terminals accessed with a fixed number of OLTs. In general, the standard split ratio of EPON is 1:32. Of course, it can support a lower or higher splitter ratio of 1:16, 1:64, or 1:128. GPON supports a typical split ratio of 1:32 or 1:64, and 1:128 is available in some systems.
So, is the higher the split ratio the better? No, an excessive split ratio raises the optical module costs and decreases the performance (transmission distance typically). Say, a GPON SFP is more expensive than an EPON SFP. The more branch users served, the more the optical attenuation of PON insertion loss. For instance, when the split ratio is 1:16, the max transmission distance is 20 km; when the split ratio is 1:32, it can only reach up to 10 km.
GPON vs EPON — Architecture Layering
EPON has a simple networking architecture. It directly uses an Ethernet frame to transmit data, voice, and video. Or IP-based data into Ethernet frame and then forward via PON.
GPON has three "layer 2". First, TDM and Ethernet frames are wrapped into GEM frames. Second, ATM cells and GEM frames are encapsulated into the GTC frame and delivered via PON.
GPON vs EPON — Versatility
Multi-Service
GPON complies with G.984.X standard, which supports triple-play — data, voice, video, meeting the needs of carrier-grade full service.
Quality of Service (QoS)
GPON has inherent QoS full service, while EPON requires the extra cost for manually configuring the VLAN label to enable QoS.
OAM Security Management
GPON specifies management in various layers: OAM, PLOAM (Physical Layer OAM), and OMCI (ONT Management and Control Interface). Each message control channel performs its duties to achieve full OAM security management.
EPON only has simple OAM functions, such as FEF (far-end fault), loopback, and monitoring.
GPON vs EPON — Cost
To compare GPON vs EPON cost, first, we should understand the network component cost. OLT, ONU, and ODN are three necessary units to compose GPON and EPON. ODN elements include fibers, ODF, optical splitter, optical connector, etc. If the user numbers are the same, the cost in the ODN may not be much different. However, optical modules and application-specific integrated circuits deployed in OLT and ONU make a big difference. The FPGA-based IC chip of GPON is much more expensive than the ASIC-based chipset of EPON.
Here, you might blurt out:" EPON is cheaper than GPON." Wait, don't jump to conclusions. Besides the equipment cost, there is subscriber cost. Given that GPON is performance optimized for a higher split ratio, higher bandwidth, and transmission efficiency, one can save a fortune by OLT number reduction. This also leads to a reduction in lifecycle costs.
For a quick read, the table below summarizes the main differences.
GPON vs EPON: Which is Better?
GPON vs EPON, which is better? A hot topic on the Internet that aroused intense discussion. However, there is no certain either/or conclusion. As both two have their advantages and limitations. And the option is based on your current situations and business needs, such as networking budget, fiber access cost, end-user numbers, advanced requirements such as QoS and security management.
Here are the pros and cons of EPON vs GPON listed for your reference.
EPON Advantages:
simple networking architecture
lower component cost
support encryption in both streams
GPON Advantages:
the highest bandwidth of 2.48Gbit/s in downstream
multi-service support
more end-users coverage up to 128 ONU
high transmission efficiency
support encryption in downstream
cost-efficient for large telecom users
EPON Limitations:
quality of service (QoS)
OAM management
security
GPON Limitations:
complex networking technology
expensive GPON components such as GPON optics
Conclusion
After comparing FTTH GPON vs EPON and listing their strengths and weaknesses. Here is a brief point for friends who need a quick read to get buying guide.
GPON is favored by carrier-grade users who require high bandwidth, high-density access, triple play multi-service, and advanced features such as QoS, security, and ATM as the backbone.
EPON is user-friendly for residential and SMBs who are sensitive to networking complexity, cost-efficiency and have no high requirements for advanced features such as security, QoS and ATM.
Looking back on the PON development history, the access network sees momentum in the adoption of optical fiber transmission for higher bandwidth and versatility. For current FTTH, EPON and GPON are the mainstream technologies. Moving forward, 10G EPON and 10G GPON have seen their market in FTTB (fiber to the building) to provide a higher data rate over a longer reach while carrying more users. It can be expected that shortly, the high-speed and long-haul 25G/40G/100G passive optical network may become the next newborn.
Related Article:
What is Optical Distribution Frame (ODF)?
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