From EPON to XGS-PON: The 10G Access Network Migration

The PON generations in one table

| Standard | Downstream | Upstream | Symmetry | Typical module | |---|---|---|---|---| | EPON | 1.25G | 1.25G | Symmetric | 1.25G EPON OLT/ONU | | 10G EPON | 10G | 10G or 1G | Both variants | 10G EPON OLT/ONU | | GPON | 2.5G | 1.25G | Asymmetric | 2.5G GPON OLT/ONU | | XGPON1 | 10G | 2.5G | Asymmetric | XGPON OLT/ONU | | XGS-PON | 10G | 10G | Symmetric | XGS-PON OLT/ONU |

Symmetric vs asymmetric: why it decides the design

XGPON1 offers 10G downstream but only 2.5G upstream. XGS-PON offers 10G in both directions. That single difference determines:

• Split ratio headroom. Symmetric 10G supports more subscribers per OLT port at a usable experience level, so fewer OLT ports are needed.
• Upstream capacity planning. Video calls, cloud backup and remote work have pushed upstream demand up far faster than the industry expected in the 2010s. Asymmetric designs can become upstream-constrained.
• Migration path. XGS-PON is generally the longer-lived choice for new builds, because upstream demand is not going to decrease.

OLT versus ONU: different modules, different priorities

OLT side (the central office):

• Higher transmit power and tighter wavelength control
• Burst-mode receive capability
• Longer design life — OLT ports are not replaced often, so qualify carefully
• Common reaches: 20 km

ONU side (the subscriber):

• Cost is the dominant constraint, because there is one per subscriber
• Continuous-mode transmit
• Must survive lower-cost installation environments
• Common reaches: 20 km

The devices inside: BOSA

The bidirectional optical subassembly is where transmit and receive share a single fiber — which is exactly what a PON requires. PON deployments typically use:

• OLT BOSA — EML laser with APD-TIA receiver for higher transmit power and sensitivity
• ONU BOSA — DFB laser with APD-TIA or PIN-TIA receiver, in a pigtailed SC/UPC package

Getting the BOSA selection right is often what determines whether a PON design hits its optical budget, especially with an optical split ratio of 1:64 or 1:128.

Migration advice

1. Deploy XGS-PON capable OLTs even if XGPON service is the initial offering — the port hardware is the slow, expensive part to change.
2. Standardise on SC/UPC pigtailed ONU BOSAs to reduce spares inventory.
3. Verify reach and split-ratio budget with the actual OLT and ONU transmit powers before ordering in volume.

Canjin Technology supplies EPON, XGPON and XGS-PON OLT/ONU modules, plus the matching BOSA devices with full transmit power and sensitivity specifications.