Ethernet passive optical network

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Ethernet passive optical network (EPON) and Gigabit Ethernet passive optical network (GEPON) are standard (IEEE 802.3ah) implementations of Ethernet in the first mile (EFM) over fiber. The technology was introduced as EPON with speeds of up to 100 Mbps. When the 1 Gbps rates were possible the GEPON designation was accepted. The standards do not differentiate between EPON and GEPON.

GEPON uses the existing 802.3 MAC and frame structure and adds a reconciliation layer below the MAC to adapt to the point-to-multipoint nature of the PON. The reconciliation layer makes the point-to-multipoint Physical Layer look like a series of point-to-point links and the headend look like an Ethernet switch. The Multipoint Control Protocol (MPCP) is used to control access to a point-to-multipoint facility for upstream transmissions. In the MPCP the headend grants permits to one subscriber at a time for transmission. The scheme is time division multiple access (TDMA) between the stations. The headend can “pause” a station from transmitting.

The Physical Layer speeds of the GEPONs are 1.25 Gbps with a throughput of 1 Gbps. The standard can extend to 10 Gbps in the future. The upstream (1310 nm) and downstream (1490 nm) transmissions are wavelength division multiplexed (WDM) on the same fiber.