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Passive optical network
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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 service providers (ISP) and their customers. In this use, a PON has a point-to-multipoint topology in which an ISP uses a single device to serve many end-user sites using a system such as 10G-PON or GPON. In this one-to-many topology, a single fiber serving many sites branches into multiple fibers through a passive splitter, and those fibers can each serve multiple sites through further splitters. The light from the ISP is divided through the splitters to reach all the customer sites, and light from the customer sites is combined into the single fiber. Many fiber ISPs prefer this system.
A passive optical network consists of an optical line terminal (OLT) at the service provider's central office (hub), passive (non-power-consuming) optical splitters, and a number of optical network units (ONUs) or optical network terminals (ONTs), which are near end users. There may be amplifiers between the OLT and the ONUs. Several fibers from an OLT can be carried in a single cable. A PON reduces the amount of fiber and central office equipment required compared with point-to-point architectures with dedicated connections for every user. A passive optical network is a form of fiber-optic access network. Bandwidth is commonly shared among users of a PON.
In most cases, downstream signals are broadcast to all premises sharing multiple fibers. Encryption can prevent eavesdropping.
Upstream signals are combined using a multiple access protocol, usually time-division multiple access (TDMA).
Passive optical networks were first proposed by British Telecommunications in 1987.
Two major standard groups, the Institute of Electrical and Electronics Engineers (IEEE) and the Telecommunication Standardization Sector of the International Telecommunication Union (ITU-T), develop standards along with a number of other industry organizations.
The Society of Cable Telecommunications Engineers (SCTE) also specified radio frequency over glass for carrying signals over a passive optical network. CableLabs has developed coherent PON (CPON) that runs at 100 Gbit/s symmetrically and supports split ratios of up to 1:512. Coherent means it only needs a single wavelength of light to operate.
Starting in 1995, work on fiber to the home architectures was done by the Full Service Access Network (FSAN) working group, formed by major telecommunications service providers and system vendors. The International Telecommunication Union (ITU) did further work, and standardized on two generations of PON. The older ITU-T G.983 standard was based on Asynchronous Transfer Mode (ATM), and has therefore been referred to as APON (ATM PON). Further improvements to the original APON standard – as well as the gradual falling out of favor of ATM as a protocol – led to the full, final version of ITU-T G.983 being referred to more often as broadband PON, or BPON. A typical APON/BPON provides 622 megabits per second (Mbit/s) (OC-12) of downstream bandwidth and 155 Mbit/s (OC-3) of upstream traffic, although the standard accommodates higher rates.
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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 service providers (ISP) and their customers. In this use, a PON has a point-to-multipoint topology in which an ISP uses a single device to serve many end-user sites using a system such as 10G-PON or GPON. In this one-to-many topology, a single fiber serving many sites branches into multiple fibers through a passive splitter, and those fibers can each serve multiple sites through further splitters. The light from the ISP is divided through the splitters to reach all the customer sites, and light from the customer sites is combined into the single fiber. Many fiber ISPs prefer this system.
A passive optical network consists of an optical line terminal (OLT) at the service provider's central office (hub), passive (non-power-consuming) optical splitters, and a number of optical network units (ONUs) or optical network terminals (ONTs), which are near end users. There may be amplifiers between the OLT and the ONUs. Several fibers from an OLT can be carried in a single cable. A PON reduces the amount of fiber and central office equipment required compared with point-to-point architectures with dedicated connections for every user. A passive optical network is a form of fiber-optic access network. Bandwidth is commonly shared among users of a PON.
In most cases, downstream signals are broadcast to all premises sharing multiple fibers. Encryption can prevent eavesdropping.
Upstream signals are combined using a multiple access protocol, usually time-division multiple access (TDMA).
Passive optical networks were first proposed by British Telecommunications in 1987.
Two major standard groups, the Institute of Electrical and Electronics Engineers (IEEE) and the Telecommunication Standardization Sector of the International Telecommunication Union (ITU-T), develop standards along with a number of other industry organizations.
The Society of Cable Telecommunications Engineers (SCTE) also specified radio frequency over glass for carrying signals over a passive optical network. CableLabs has developed coherent PON (CPON) that runs at 100 Gbit/s symmetrically and supports split ratios of up to 1:512. Coherent means it only needs a single wavelength of light to operate.
Starting in 1995, work on fiber to the home architectures was done by the Full Service Access Network (FSAN) working group, formed by major telecommunications service providers and system vendors. The International Telecommunication Union (ITU) did further work, and standardized on two generations of PON. The older ITU-T G.983 standard was based on Asynchronous Transfer Mode (ATM), and has therefore been referred to as APON (ATM PON). Further improvements to the original APON standard – as well as the gradual falling out of favor of ATM as a protocol – led to the full, final version of ITU-T G.983 being referred to more often as broadband PON, or BPON. A typical APON/BPON provides 622 megabits per second (Mbit/s) (OC-12) of downstream bandwidth and 155 Mbit/s (OC-3) of upstream traffic, although the standard accommodates higher rates.
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