GPON Overview in 10 Items

1. GPON is a shared-fiber FTTH broadband access technology standardized by the ITU in G.984,
2. Almost all GPON systems are single fiber, but dual fiber is allowed in the standard,
3. The GPON OLT is the network concentrator, and the ONT serves a single residence (ONU generally means an ONT serving several subscribers),
4. GPON is specified to 2.488 Gbps symmetrical, but most all systems run 2.488 Gbps downstream and 1.244 Gbps upstream,
5. GPON wavelengths are 1490 nm down and 1310 nm up,
6. B+ optics provides a 20km reach and a 32x split ratio (32 subscribers served by a single shared fiber).  Higher split ratios mean much less distance – around 5km with 64x split ratio.  C+ optics provide 64x split while retaining 20km reach.
7. On GPON, downstream from OLT to ONTs is broadcast, and upstream is TDMA with each ONT transmitting in turn. Upstream can be oversubscribed with Dynamic Bandwidth Assignment or DBA,
8. GPON natively supports Ethernet, ATM, and TDM, but most systems run just Ethernet (GFP),
9. RF Video is downstream at 1550 nm and about 20dB (100x)  hotter than the GPON signal,
10. With RFoG, a fourth wavelength, transmitted from ONTs to OLT and usually at 1590nm or 1610nm, provides an upstream channel for DOCSIS cable modem service.

GPON Network Diagram

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