ITU-T The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) is one of the three Sectors (branches) of the International Telecommunication Union (ITU). It is responsible for coordinating Standardization, standards fo ...

G.984 is the series of standards for implementing a gigabit-capable

passive optical network A passive optical network (PON) is a fiber-optic telecommunications network that uses only ''unpowered'' devices to carry signals, as opposed to electronic equipment. In practice, PONs are typically used for the '' last mile'' between Internet ...

(GPON). It is commonly used to implement the link to the customer (the ''last kilometre'', or ''last mile'') of fibre-to-the-premises ( FTTP) services. 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 ( optical line termination) and the ONTs ( optical network terminals) is 2.4Gbit/s down, 1.2Gbit/s up, or rarely symmetric 2.4Gbit/s, shared between up to 128 ONTs using a

time-division multiple access Time-division multiple access (TDMA) is a channel access method for shared-medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, ...

(TDMA) protocol, which the standard defines. GPON specifies protocols for error correction ( Reed–Solomon) and encryption ( AES), and defines a protocol for line control ( OMCI) which includes authentication (GPON serial number and/or PLOAM password). Unlike the previous EPON standard, which has a much simpler topology, GPON encapsulates Ethernet packets into virtual GEM ports, TCONT queues and VLANIDs via OMCI. The exact kind of fibre cable and connectors to use is undefined but is broadly using SC/APC connectors. The primary optical transmitter, known as the optical line terminal (OLT), is housed within the central office of the telecommunications operator. A laser in the OLT injects photons from the central office into a glass-and-plastic fiber-optic cable that terminates at a passive optical splitter. The splitter divides the single signal from the central office into many signals that can be sent to up to 64 consumers. The number of consumers serviced by a single laser is determined by the operator's engineering criteria; operators may opt to reduce the number to 32 consumers. Furthermore, the operator may choose to divide the signal twice, for example, once into eight and again farther down the line. The maximum distance between the central office and the site can be 20 kilometers, however operators will normally limit it to 16 kilometers in order to maintain a high level of service. In contrast to

ADSL Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over Copper wire, copper telephone lines than a conventional voiceband modem ...

technology, which deteriorates as the distance between the central office and the household rises, with severe signal loss beyond 3km, all customers may enjoy high-speed network access within the 16km range of a fibre central office.

The standards

The first version of GPON was ratified in 2003. 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. The most recent version comprises seven parts: * G.984.1 : General characteristics, 2008, with amendment 1 (2009) and 2 (2012) * G.984.2 : Physical Media Dependent (PMD) layer specification, 2003, with amendment 1 (2006) and 2 (2008) * G.984.3 : Transmission convergence layer specification, 2008, with amendments 1 (2009), 2 (2009), 3 (2012) and erratum 1 (2010) * 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) * G.984.5 : Enhancement Band, 2014, Coexistence with future WDM PON technology on the same medium * G.984.6 : Reach extension (2008), with amendments 1 (2009) and 2 (2012) * G.984.7 : Long reach (2010) 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 GPON specifics that are not defined in G.988. Future work on the PON management model is expected to appear only in the GPON space.

Security

Security issues in the G.984 standard series include the possibility of eavesdropping on upstream traffic, replay attacks, PLOAM messages that are not integrity protected and

denial of service In computing, a denial-of-service attack (DoS attack) is a cyberattack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host co ...

to other subscribers on the same link.

References

{{reflist ITU-T recommendations ITU-T G Series Recommendations Telecommunication protocols

The standards

Security

See also

Further reading

References