GPON Architecture and What It Means

Gigabit Passive Optical Networks (GPON) is an Optical System for the Access Networks, based on ITU-T specifications G.984 series. It offers a 20 km reach with a 28dB optical budget using class B+ optics with a 1:32 split ratio. GPON offers point-to-multipoint access mechanism and can transport different traffic, including ATM, Ethernet, and TDM (PSTN, ISDN, E1, and E3) traffic. Compared to other types of computer networks, notably BPON and APON, GPON has higher bandwidths. This allows it to be used in several scenarios, notably in FTTx networks.

GPON technology can deliver voice, data, and IP video with sufficient stability, thus suitable for use in home (FTTH) transmission and small businesses. Here’s an in-depth look at GPON Architecture. 

GPON Architecture     

The main characteristic of GPON architecture is the use of passive splitters in the fiber distribution network, allowing one single feeding fiber from the provider's central office to serve multiple homes and small businesses.

GPON Architecture features a tree topology maximizing the coverage with minimum network splits therefore reducing optical power. The FTTH access network encompasses five areas: a core network area, a central office area, a feeder area, a distribution area, and a user area. 

Core Network 

The core network encompasses the internet service provider ISP equipment, cable TV provider equipment, and a PSTN (packet-switched or the legacy switched). 

Central Office 

The Central Office functions to host the OLT and ODF (optical distribution frames) and provide the necessary powering. It may sometimes include some of the components of the core network. An optical splitter is installed somewhere between the CO and the subscribers. Also, a GPON Optical Network Terminal (ONT) is installed at each subscriber's home; Voice, video, and data traffic is delivered across the single GPON downstream wavelength.

Feeder Network

The feeder area extends from ODF in the central office to the distribution points. The points are referred to as Fiber Disruption Frames FDT, where level-1 splitters are placed. The feeder cable is usually linked as ring topology starting from a GPON port and ending in another GPON port.  

Distribution Network 

The distribution cable connects the level-1 splitter found inside the FDT with the level-2 splitter. The level-2 splitter is usually hosted in the Fiber Access Terminal FAT, which is often placed at the neighborhood entrance. 

User Area 

In the user area, drop cables are used to connect the level-2 splitter inside the FAT to the subscriber premises. An aerial drop cable is usually terminated at the subscriber's home entrance with a Terminal Box TB. An indoor drop cable links the TB to an Access Terminal Box ATB which resides inside the home. The final link is between the ONT and ATB via a patch cord. 

Components of GPON FTTH Access Network 

A GPON FTTH access network consists of three main components: optical line terminal (OLT), optical splitters, and optical network terminal (ONT). 

Optical Line Terminal (OLT) 

OLT is a device that functions as the service provider endpoint of a passive optical network. It’s an active Ethernet aggregation device that is usually located in a data center or the main equipment room. OLT is the main driver of the FTTH system functioning to convert the optical signals to electric signals and relay them to a core Ethernet switch. OLT replaces multiple layer 2 switches at distribution points connected with backbone cabling or horizontal cabling via optical splitters.

ONT (Optical Network Terminal) 

ONT links to the OLT via optical fiber. In a GPON network, a transceiver in the ONT functions to link a customer premises to the central office OLT physically. 

Optical Splitter 

As the name implies, the optical splitter divides the signal's power into a given number of fibers leaving the splitter. Usually, three or more levels of fibers correspond to two or more levels of splitters. The passive optical splitter has some unique characteristics such as broad wavelength range, low insertion loss, and minimal dimensions.   

Conclusion on GPON Architecture

Gigabit Passive Optical Network (GPON) stands out among other passive optical networks thanks to its immense benefits. This network style's primary benefit is the use of passive splitters in the fiber distribution network allowing for a point-to-multipoint access mechanism. By employing two access points, GPON significantly reduces the chance of a network failure. GPON architecture encompasses five principal components, as discussed above.