PON- Passive Optical Network, EPON vs GPON

Starting in 1995, formed by major telecommunications service providers and system vendors. The International Telecommunications Union (ITU) did further work, and standardized on two generations of PON. The older ITU-T G.983 standard was based on Asynchronous Transfer Mode (ATM), and has therefore been referred to as APON (ATM PON). Further improvements to the original APON standard – as well as the gradual falling out of favor of ATM as a protocol – led to the full, final version of ITU-T G.983 being referred to more often as broadband PON, or BPON. A typical APON/BPON provides 622 megabits per second (Mbit/s) (OC-12) of downstream bandwidth and 155 Mbit/s (OC-3) of upstream traffic, although the standard accommodates higher rates.

Passive Optical Networks (PON) are point-to-multipoint optical networks with no active elements in the signals’ path from source to destination. The only interior elements used in such networks are passive combiners, couplers, and splitters. It starts from the optical line terminal (OLT) in the central office and ends at the optical network (ONU) at the customer’s home

Types

APON (ATM Passive Optical Network) first Passive optical network standard. It was used for business applications, and based on ATM.

BPON (Broadband PON) is commonly offered at 622 Mbps downstream and 155 Mbps upstream. Its ATM structure and bandwidth limits make it less than ideal for video. Development has stopped on BPON. BPON networks will over time be converted to EPON or GPON. There are approximately 2 million BPON users worldwide.

EPON (Ethernet PON) generally delivers 1 Gbit/s symmetrical bandwidth.Employs a single Layer 2 network that uses Internet Protocol (IP) to carry data, voice, and video, generally delivers 1 Gbit/s symmetrical bandwidth. Costs of EPON equipment are approximately 10 percent of the costs of GPON equipment because it does not require multi-protocol conversions, and the result is a lower cost of silicon. In GPON, there are three management systems for the three Layer protocols. EPON equipment is rapidly becoming cost competitive with VDSL.

GE-PON (for Gigabit Ethernet PON) has a higher installed volume than all other PON technologies combined. EPON is found widely in Asia.

GPON (Gigabit Ethernet PON) provides three Layer 2 networks: ATM for voice, Ethernet for data and proprietary encapsulation for voice. Promises 1.25 Gbit/s or 2.5 Gbit/s downstream and upstream bandwidths scalable from 155 Mbit/s to 2.5 Gbit/s. GPON does not support multi-cast services. This makes support for IP video more bandwidth-consuming.

PON technology is getting more and more attention by the telecommunication industry as the “last mile” solution. Advantages of using a PON for local access networks are numerous:

• A PON allows for longer distances between central offices and customer premises. While with the Digital Subscriber Line (DSL) the maximum distance between the central office and the customer is only 18000 feet (approximately 5.5 km), a PON local loop can operate at distances of over 20 km. A PON minimizes fiber deployment in both the local exchange and the local loop.
• A PON provides higher bandwidth due to deeper fiber penetration. While the fiber-tothe-building (FTTB), fiber-to-the-home (FTTH), or even fiber-to-the-PC (FTTPC) solutions have the ultimate goal of fiber reaching all the way to customer premises, fiber-tothe-curb (FTTC) may be the most economical deployment today.
• As a point-to-multipoint network, a PON allows for downstream video broadcasting. A PON eliminates the necessity of installing multiplexers and demultiplexers in the splitting locations. A PON allows easy upgrades to higher bit rates or additional wavelengths.

PON Topologies

(a) Tree topology (c) Ring topology

(b) Bus topology (d) Tree with redundant trunk

Conclusion:

Difficult to say GPON is better than EPON, or vice verse. They have their +- When we talk about IP/Ethernet services, EPON is more suitable and cost effective. While GPON has its own benefits in higher bandwidth, faster transmission rate and supporting triple-play services. I can say EPON is still the mainstream of PON, especially in the Asian countries, but GPON is expanding in a nice way.