A Comparison of FTTH technology- GPON or EPON

Fiber to the home (FTTH) is the delivery of a communications signal over optical fiber from the Telco or Internet Service Provider’s switching equipment all the way to a home or business, thereby replacing existing copper infrastructure such as telephone wires and coaxial cable.

Fiber to the home is a relatively new and fast growing method of providing vastly higher bandwidth to consumers and businesses, and thereby enabling more robust video, internet and voice services.        

Connecting homes directly to fiber optic cable enables enormous improvements in the bandwidth that can be provided to consumers. Current fiber optic technology can provide two-way transmission speeds of up to upto Gigabits per second. Ongoing improvements in fiber optic equipment are constantly increasing available bandwidth without having to change the fiber. That’s why fiber networks are “future proof.”

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. The main disadvantage is a shorter range of coverage limited by signal strength. While an active optical network (AON) can cover a range to about 100 km (62 miles), a PON is typically limited to fiber cable runs of up to 20 km (12 miles). PONs also are called fiber to the home (FTTH) networks.

PON has primarily 2 technology variants

 GPON

Gigabit PON is standard ITU-T as the G.984.x standards–an addition to ITU-T recommendation, G.983, which details broadband PON (BPON). GPON uses optical wavelength division multiplexing (WDM) so a single fiber can be used for both downstream and upstream data. A laser on a wavelength (λ) of 1490 nm transmits downstream data. Upstream data transmits on a wavelength of 1310 nm. If TV is being distributed, a wavelength of 1550 nm is used.

·        GPON supports 2.5 Gbit/s downstream and 1.25 Gbit/s upstream

·        Each GPON Ports up to 128 users. The typical split of a single fiber is 1:32 or 1:64. That means each fiber can serve up to 32 or 64 subscribers. Split ratios up to 1:128 are possible in GPON systems

 The latest version of GPON is a 10-Gigabit version called XGPON, or 10G-PON. As the demand for video and over the top (OTT) TV services has increased, there is an increasing need to boost line rates to handle the massive data of high-definition video. XGPON serves this purpose. The ITU standard is G.987.

XGPON’s maximum rate is 10 Gbits/s (9.95328) downstream and 2.5 Gbits/s (2.48832) upstream. Different WDM wavelengths are used, 1577 nm downstream and 1270 nm upstream. This allows 10-Gbit/s service to coexist on the same fiber with standard GPON. Optical split is 1:128, and data formatting is the same as GPON. Maximum range is still 20 km.

EPON

The Institute of Electrical and Electronic Engineers (IEEE) developed another newer PON standard. Based on the Ethernet standard 802.3, EPON 802.3ah specifies a similar passive network with a range of up to 20 km. It uses WDM with the same optical frequencies as GPON and TDMA. The raw line data rate is 1.25 Gbits/s in both the downstream and upstream directions. You will sometimes hear the network referred to as Gigabit Ethernet PON or GEPON.

There is also a 10-Gbit/s Ethernet version designated 802.3av. The actual line rate is 10.3125 Gbits/s. The primary mode is 10 Gbits/s upstream as well as downstream. A variation uses 10 Gbits/s downstream and 1 Gbit/s upstream. The 10-Gbit/s versions use different optical wavelengths on the fiber, 1575 to 1580 nm downstream and 1260 to 1280 nm upstream so the 10-Gbit/s system can be wavelength multiplexed on the same fiber as a standard 1-Gbit/s system.

Figure : Typical PON Network Architecture

GPON is well deployed & adopted technology worldwide while EPON is popular primarily in China, Japan and some other Asian countries but dominated by Ecosystems of OEM’s and vendors from China. Followings are comparision on specific parameters;-

1.      Security: EPON system, the OLT broadcasts downstream data to all ONU. Therefore, downstream data may be received by unauthorized ONUs, causing security risks. the GPON system uses the AES-128 encryption algorithm to encrypt plain text data packets and broadcasts them in ciphertext. AES-128 algorithm uses a key to change a 128-bit plaintext data into another 128-bit ciphertext data for broadcasting by using a series of mathematical operations. GPON is a secured Technology however EPON relies on Ethernet protocols for security. Security has been a major reason for wide adoption of GPON worldwide.

2.      Split Ratio: GPON supports 1:128 Split ratios while EPON Systems support 1:32 Split ratio.  in practical field scenario. Hence GPON Port can cater to 128 Subscribers while EPON port serves only 32 subscribers. Hence 8 Port GPON OLT device can cater upto 1000 Subscribers while 8 Port GEPON OLT device can provide connectivity to 256 Subscribers.

3.      Bandwidth: GPON supports 2.5Gbps downlink while EPON supports 1.25GPON downlink. Moreover, there is a huge overhead on EPON packets hence giving only 1 Gbps bandwidth available only towards downlink. In case, 32 Customers are getting catered by 1 EPON port, the best possible bandwidth available during peak time would be around 30 Mbps (1Gbps/32) which is much lower than envisaged national average 50 Mbps. In the case of GPON, the bandwidth availability per Customer would be 78 Mbps. Hence GPON has become a de-facto national technology of most of the countries.

4.      QOS & OAM:  GPON is defined by ITU-T standardization taking in cognizance all transport level requirements for trouble-shooting the faults, defining protection schemes, well thought-out Traffic containers for different types of traffic ensuring the desired Quality of services as per the Service requirements.

GPON standard ITU-T G.984 defines PLOAM (Physical Layer OAM) at the physical layer, OMCI (ONT Management and Control Interface) at the upper layer, and OAM management at multiple levels. PLOAM enables data encryption, status detection, error monitoring and other functions. The OMCI channel protocol is used to manage the services defined by the upper layer, including the ONU function parameter set, the type and quantity of T-CONT services, QoS parameters, configuration information and performance statistics. OMCI channel automatically notifies the system of running events, Troubleshooting, performance and safety management.

EPON, on the other hand, has no such well-defined OAM parameters for managing, configuring the services. There is no dedicated OAM channel defined by IEEE standard hence the mechanism of managing the ONUs relies on Ethernet OAM regulated by IEEE 802.3ah which is a relatively slow protocol. It simply defines the ONT far-end fault indication, loopback, and link monitoring. Hence EPON has very limited OAM for the deployment of such a large scale and hence not being adopted. QOS has been one of the major pressing issues for EPON . There has been some algorithm like Full Priority Scheduling /Interval priority scheduling for assigning the Bandwidth however it has been relative slow, adds overheads & introduces latency hence making it unfit for deployment of technology which has its major used case of Quality of Service.

5.      Eco-System: Countrywide/Statewide operators (Airtel, JIO, Verizon, Bharatnet States, BSNL & etc) have adopted GPON while EPON being available at very cheap prices are being deployed by Cable Service Providers, BSNL partners & CSC entrepreneur. The cost competiveness of EPON equipment are driven majorly by following factors.

a.      Chinese/Taiwan/Korean Companies manufacturing EPON devices at a large scale. Almost all of the Chinese EPON companies(V-sol, C-Data & etc) are using ZTE chipsets & its design to produce these devices with backdoors in its software.

b.      EPON follows IEEE standards and hence Ethernet Switches chipsets are widely available in the market hence providing them advantage of Economy of Scale and hence driving the cost down

Vast eco-system is available for GPON with OEMs and operators from India, US, Korea and Europe focusing on it because of its advantages, robustness and secureness over EPON. Major OEMs for GPON are Tejas, Alphion (India) , ITI, Nokia(Finland), DASAN (South Korea),Calix(US), Genexis (Sweden), ADTRAN(US) & etc. However in order to ensure to come down to the pricing levels of EPON market, there is required to be focused R&D effort on components, software & the chipsets with market projections of lacks of devices reaping the economy of scale advantage.

Major Differences for GPON & EPON technologies are tabulated below:

Conclusion

There are advantages to using both GPON and EPON systems. In comparison, it would be fair to conclude that GPON performs better than EPON overall, however EPON would be preferable in terms of cost and time saving. GPON has more vendor ecosystems and it has better Management and security features than EPON.

Author, Pradeep Mishra ([email protected])

(Author is a telecom and IT Professional with experience of more than 25 years. Views and analysis are in personal nature. All IPR’s belongs to the respective organizations and their reference is only for understanding)

Reference and Credits

1.      https://www.electronicdesign.com/unused/article/21799542/whats-the-difference-between-epon-and-gpon-optical-fiber-networks

2.      https://www.heavyreading.com/document.asp?doc_id=209412#:~:text=Vendors%20with%20EPON%20optical%20transceiver,OPLK)%20and%20Source%20Photonics%20Inc.

3.      https://www.carritech.com/news/epon-vs-gpon/

4.      https://www.zte.com.cn/global/about/magazine/zte-technologies/2007/5/en_90/161787.html

5.      https://www.fujitsu.com/us/Images/EPONvsGPON.pdf

6.      Consultation with Industry experts