Passive Optical Networks, PON, is another technology used in some FTTH networks. In PON networks the last mile access is shared by multiple users.

The Optical Line Terminal (OLT) installed in a central office location by the network operator connects to several PON segments. A fiber from the OLT goes out into a PON segment where a passive optical splitter is used to divide the light into up to 128 further downlink fibers that connect to an Optical Network Unit (ONU) or Optical Network Terminal (ONT) in a home or business.

The use of a passive optical splitter means that the light is divided – split – in the downstream direction and combined in the upstream direction. Because the splitter is passive, the light signal is not regenerated so it becomes weaker when passing through the splitter, which affect distance between the OLT and ONT/ONU.

Splitting allows the single fiber from the OLT to be shared among up to 128 ONT/ONUs but this also means that the bandwidth of the PON segment is shared among all the connected ONT/ONUs. Even if XGS-PON is used it still means that 10Gbit/s is shared among up to 128 ONT/ONUs. While PON do allow unused bandwidth to be consumed, a busy PON segment will have less bandwidth available per user compared to a 10Gbit/s P2P network where the bandwidth is dedicated per user.

Thus in a PON network – even with XGS-PON - it is not feasible to deliver 10Gbit/s services since a single ONT/ONU then would be able to consume all bandwidth on the PON segment.

PON networks are complex in that each ONT/ONU must be controlled by the OLT to make sure that two ONT/ONUs are not sending data at the same time. This would not work on the shared segment. For this reason, the management communication (OMCI) between OLT and ONT/ONU is important. There are often interoperability issues with the OMCI management communication between different vendors of OLT and ONT/ONU equipment, forcing network operators to select the OLT and ONT/ONU from the same vendor to have a working solution.

There are multiple PON technologies. The most common ones today in Europe are GPON that is now getting replaced by XGS-PON, both standardized by the ITU. In Asia EPON, which is standardized by IEEE is popular.

A challenge in PON network design is scalability and upgradeability – what to do when there is not enough bandwidth available on a PON segment. Options include to decrease the split ratio (divide the PON segment into multiple segments) or to upgrade some or all users to a later generation PON which may require upgrades of OLT and ONT/ONUs. Given current service speeds it is not recommended to use more than 1:32 split.

PON networks are typically combined with a Broadband Network Gateway (BNG) to handle the service delivery and integration with operational support systems.

Further reading about PON vs Point-to-Point

Read our article "PON and P2P - Comparing Apples and Pears".

Waystream do not work with PON technology. Our main focus is on Point-to-Point (P2P). You can read more about Point-to-Point technology and how we work with it below.