GPON / EPON

Passive Optical Network (PON) is an access technology by means of optical fiber. In these technologies, a point-to-multipoint architecture is created for the access (external plant), in which a 

Optical Line termination (OLT) device at the provider’s network is connected to several Optical Network Termination (ONT) devices. Passive optical splitters are used to distribute the signals between OLD and ONT and vice-versa. 

PON uses only passive elements in the external plant, it allows point to multipoint connections, it has a well-defined multiplexing scheme and it uses an unique OLT concentrator equipment. There are different PON schemes, among which Giga-capable PON (GPON) and Ethernet PON (EPON) are highlighted.

GPON was defined by the International Telecommunications Union (ITU) in its standard G.948 and it reaches a traffic rate of 2,488 Gbps (symmetrical or asymmetrical). It uses his own encapsulation method, GPON Encapsulation Method (GEM), which allows the transport of all the services (Ethernet, FR, etc.) directly, with no need to adapt preexisting equipment. GPON uses WDM technologies to differentiate the upstream traffic from the downstream traffic, and TDM to multiplex the traffic streams.

Ethernet PON (EPON) was defined as the standard by the Institute of Electrical and Electronics Engineers (IEEE) in the norm 802.3ah. Ethernet is used as transport technology and it reaches rates of 1250/1250 Mbps Upstream/Downstream. EPON uses the Multi Point Control Protocol (MPCP) to assign time slots, report the required bandwidth and negotiation of optical parameters, and it allows QoS in upstream and downstream traffic.

Both in GPON and EPON, upstream traffic is broadcast, which facilitates its use with multicast applications like broadcast TV.

Both norms have evolved and published their version of next generation, where transmission rates of 10 Gbps are reached. The new standards are called 10G-EPON (IEEE 802.3av) and 10-GPON (ITU G.987). The service can be offered symmetrically (10 Gbps of upload and 10 Gbps of download) or asymmetrically (10 Gbps of download, 1 Gbps of upload). 

Among the main advantages of the PON technologies, we can mention:

  • Greater bandwidth.
  • Longer distances central-subscriber.
  • Lower deployment of optic fiber.
  • Lower degradation of the signal due to electric noises immunity.
  • Repeaters or active elements are not used.
  • Lowering of investment costs, electrical and operational consumption. 

More information at: http://www.itu.int/  and http://standards.ieee.org/

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