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G.984[1], commonly known as GPON (Gigabit-capable Passive Optical Network), is a standard for passive optical networks (PON) published by the ITU-T. It is commonly used to implement the last kilometre of Fibre To The Premises (FTTP) services[2][3].

GPON puts requirements on the optical medium and the hardware used to access it, and defines the manner in which ethernet frames are converted to an optical signal, as well as the parameters of that signal. The bandwidth of the single connection between the OLT and the ONTs is 2.4 Gb/s down, 1.2 Gb/s up[1], shared between up to 128 ONTs using a Time Division Multiple Access (TDMA) protocol, which the standard defines[4]. GPON specifies protocols for error correction (Reed-Solomon) and encryption (AES), and defines a protocol for authentication (OHCI).

Though implementations of GPON share a lot of common features, many features were left undefined, thus in practice, there is little compatibility between the various implementations[5]. Specifically, the exact kind of fibre cable and connectors to use is undefined[6].

The standards[edit]

The first version of GPON was ratified in 2003[1]. Since then, it has been expanded upon and revised several times. Work on the standard continues. As of July 2018, G.984.5 is currently being revised[7]. The most recent version comprises seven parts:

  • G.984.1 : General characteristics, 2008, with amendment 1 (2009) and 2 (2012)[1]
  • G.984.2 : Physical Media Dependent (PMD) layer specification, 2003, with amendment 1 (2006) and 2 (2008)[6]
  • G.984.3 : Transmission convergence layer specification, 2008, with amendments 1 (2009), 2 (2009), 3 (2012) and erratum 1 (2010)[4]
  • G.984.4 : ONT management and control interface (OMCI) specification, 2008, with amendments 1 (2009), 2 (2009), 3 (2010), erratum 1 (2009), corrigendum 1 (2010), and an implementer's guide (2009)[8]
  • G.984.5 : Enhancement Band, 2014, Coexistence with future WDM PON technology on the same medium[7]
  • G.984.6 : Reach extension (2008), with amendments 1 (2009) and 2 (2012)[9]
  • G.984.7 : Long reach (2010)[10]

The GPON OMCI recommendation G.984.4 draws on G.983.2, which defines the BPON management model. However, G.984.4 removed all references to ATM. G.988 is a stand-alone OMCI recommendation and supersedes G.984.4 except for G-PON specifics that are not defined in G.988. Future work on the PON management model is expected to appear only in the GPON space.