What is GEPON?

The 10 Gbit/s Ethernet Passive Optical Network standard, better known as 10G-EPON allows computer network connections over telecommunication provider infrastructure. The standard supports two configurations: symmetric, operating at 10 Gbit/s data rate in both directions, and asymmetric, operating at 10 Gbit/s in the downstream (provider to customer) direction and 1 Gbit/s in the upstream direction. It was ratified as IEEE 802.3av standard in 2009.
Standardization

The Ethernet in the first mile task force of the Institute of Electrical and Electronics Engineers (IEEE) 802.3 standards committeee published standards that included a passive optical network (PON) variant in 2004. In March 2006, the IEEE 802.3 held a call for interest for a 10 Gbit/s Ethernet PON study group. According to the CFI materials, representatives from the following companies supported the formation of the study group: Advance/Newhouse Communications, Aeluros, Agilent, Allied Telesyn, Alloptic, Ample Communications, Astar-ODSM, Broadcom, Centillium Communications, China Netcom, China Telecom, Chunghwa Telecom, Cisco Systems, ClariPhy Communications, Conexant Systems, Corecess, Corning, Delta Electronics, ETRI, Fiberxon, FOTEK Optoelectronics, ImmenStar, Infinera, ITRI, KDDI R&D Labs., K-Opticom, Korea Telecom, NEC, OpNext, Picolight, Quake Technologies, Salira Systems, Samsung Electronics, Softbank BB, Teknovus, Teranetics, Texas Instruments, Telecom Malaysia, TranSwitch, UNH IOL, UTStarcom, Vitesse.
By September 2006, IEEE 802.3 formed the 802.3av task force to produce a draft standard. In September 2009, the IEEE 802 Plenary ratified an amendment to 802.3 to make 802.3av-2009 a standard.
Major milestones:

 Architecture

Symmetric (10/10G-EPON)
Symmetric-rate 10/10G-EPON supports transmit and receive data paths operating at 10 Gbit/s. The main driver for 10/10G-EPON was to provide adequate downstream and upstream bandwidth to support multi-family residential building (known in the standard as Multi Dwelling Unit or MDU) customers. When deployed in the MDU configuration, one EPON ONU may be connected to up to a thousand subscribers.
The 10/10G-EPON employs a number of functions that are common to other point-to-point Ethernet standards. For example, such functions as 64B/66B line coding, self-synchronizing scrambler, or gearbox are also used in optical fiber types of 10 Gigabit Ethernet links.
Asymmetric (10/1G-EPON)
The asymmetric 10/1G-EPON appear less challenging than the symmetric option, as this specification relies on fairly mature technologies. The upstream transmission is identical to that of the 1G-EPON (as specified in IEEE standard 802.3ah), using deployed burst-mode optical transceivers. The downstream transmission, which uses continuous-mode optics, will rely on the maturity of 10 Gbit/s point-to-point Ethernet devices.
Power budgets
The 802.3av defines several power budgets, denoted either PR or PRX. PRX power budget describes asymmetric–rate PHY for PON operating at 10 Gbit/s downstream and 1 Gbit/s upstream. PR power budget describes symmetric–rate PHY for PON operating at 10 Gbit/s downstream and 10 Gbit/s upstream. Each power budget is further identified with a numeric representation of its class, where value of 10 represents low power budget, value of 20 represents medium power budget, and value of 30 represents high power budget. The 802.3av draft standard defines the following power budgets:

Forward error correction
The 10G-EPON employs a stream-based forward error correction (FEC) mechanism based on Reed-Solomon(255, 223). The FEC is mandatory for all channels operating at 10 Gbit/s rate, i.e., both downstream and upstream channels in symmetric 10 Gbit/s EPON and the downstream channel in the 10/1 Gbit/s asymmetric EPON. Upstream channel in the asymmetric EPON is the same as in 1 Gbit/s EPON, an optional frame-based FEC using Reed-Solomon(255, 239).
Backward compatibility

The 10G-EPON standard defines a new physical layer, keeping the MAC, MAC Control and all the layers above unchanged to the greatest extent possible. This means that users of 10G-EPON can expect backward compatibility of network management system (NMS), PON-layer operations, administrations, and maintenance (OAM) system, DBA and scheduling, and so on.
Coexistence with 1G-EPON
The 802.3av standard places significant emphasis on enabling simultaneous operation of 1 Gbit/s and 10 Gbit/s EPON systems on the same outside plant. In the downstream direction, the 1 Gbit/s and 10 Gbit/s channels are separated in the wavelength domain, with 1 Gbit/s transmission limited to 1480-1500 nm band and 10 Gbit/s transmission using 1575-1580 nm band.
In the upstream direction, the 1 Gbit/s and 10 Gbit/s bands overlap. 1 Gbit/s band spreads from 1260 to 1360 nm; 10 Gbit/s band uses 1260 to 1280 nm band. This allows both upstream channels to share spectrum region characterized by low chromatic disperson, but requires the 1 Gbit/s and 10 Gbit/s channels to be separated in time domain. Since burst transmissions from different ONUs now may have different line rates, this method is termed dual-rate TDMA.
Various OLT implementations may support 1 Gbit/s and 10 Gbit/s transmissions only downstream direction, only upstream direction, or in both downstream and upstream directions. The following table illustrates which ONU types are simultaneously supported by various OLT implementations:

 Related standard

Another standards body, the International Telecommunications Union has a similar standard in the ITU-T sector, recommendation number G.987. Known as 10G-PON, it has 10 Gbit/s downstream and 2.5 Gbit/s upstream, and is intended to coexist with ITU-IT's G.984 standard known as GPON instead of the IEEE standards.