Hello, everyone!
Today, I would like to share with you the Third and final part article on FTTH-PON networks – Technology.
Table 1. Insertion loss of fiber splitters: (a) theoretical value calculated for equal division of power between ports and (b) actual data of commercial splitters for the 1260–1650 nm band
With a doubling of the split ratio, splitter loss climbs by about 3.5 dB, accounting for the majority of the OLT-ONT path's loss. The cumulative loss of the splitter and drop fiber with connections in a typical PON with a 1:32 split is around 19 dB, while 10 km of feeder fiber with 0.35 dB/km attenuation at 1260 nm and a 0.1 dB splice every 2 km contributes only 4 dB.
Splitter loss consumes up to 75 percent of the OLT-ONT loss budget in a congested urban network, which varies between 20 and 33 dB depending on the transceiver version, with 2–3 dB set aside for hardware aging, repair splices, and other factors.
Table 2. FTTH-PON systems are assigned wavelength bands (values in [nm])
.
The shortest working wavelength in a given PON (Table 2), at which commercially manufactured single-mode fibers display the maximum attenuation, is used to calculate loss.
As a result, upgrading an existing PON to a higher split ratio is difficult since there is frequently insufficient loss margin, and replacing transceiver modules with a different type that has a bigger loss budget is very expensive and involves visits to all customers.
Time division multiplexing (TDM) of data packets sent in both directions is used to share OLT bandwidth between many ONTs. In GPON, XG-PON, and XGS-PON systems, the frame duration is 125 seconds, but in EPON it is 2 milliseconds.
The distances between the OLT and each ONT in a typical PON are enormous, with commensurate transmission delays. A PON spanning one apartment complex with a single splitter and all connections to units built with patch cords of equal length is an exception to this requirement.
FTTH-PON equipment must be able to withstand (compensate) differential fiber distances of up to 20 km, which equates to a round-trip differential delay of 200 seconds. When ONT is turned on for the first time, the transmission delay among OLT and ONT is measured, a process known as "ranging."
You are welcome to leave a message and exchange in the comment area. Thank you!
