An OLT (Optical Line Terminal) is a key component in passive optical networks (PONs) that are widely used for fiber to the home/premises (FTTH/FTTP) broadband networks. OLTs connect the service provider's backbone network to the optical distribution network and customer premises equipment. Here is an overview of how OLTs work:
Multiplexing and demultiplexing signals - An OLT multiplexes downlink signals and demultiplexes uplink signals to allow many customers to share the same fiber optic cable. This makes PON networks efficient and cost-effective.
Managing the PON network - The OLT manages the registration, authentication and configuration of the optical network terminals (ONTs) at customer locations. It provisions services and bandwidth to ONTs.
Traffic aggregation - The OLT aggregates the traffic from multiple ONTs onto the optical distribution network to pass to the service provider's core network. This concentrates traffic efficiently.
Quality of Service (QoS) - The OLT classifies traffic into different QoS classes and applies priority and bandwidth management to meet service level agreements.
In a PON architecture, the OLT sits in the service provider's central office connected to their core router. A single OLT can support up to 128 ONTs, depending on the PON technology.
The OLT connects to an optical splitter through trunk fiber. This splits the fiber out to individual customer locations, creating a tree network topology. The optical splitter passive, with no power requirement.
At the customer site, the fiber connects to an ONT. This provides the Ethernet and/or wireless connectivity for the user's equipment.
The OLT uses time division multiplexing (TDM) to share the fiber connection to the splitter between multiple ONTs.
Downstream, the OLT broadcasts data to all ONTs in the PON. Each ONT reads the data addressed to it, ignoring other data.
Upstream, the OLT assigns timeslots to each ONT for transmitting data. This prevents collisions as only one ONT transmits at a time.
The delay between timeslots is tightly controlled to avoid gaps in transmission. The OLT synchronizes transmissions by sending timing information to ONTs.
The OLT provisions and authenticates ONTs when they connect to the PON using security keys. The OLT then configures services, assigns VLANs and sets bandwidth profiles.
During operation, the OLT monitors each ONT's status and usage. It can remotely manage, configure and troubleshoot ONTs from the central office.
If an ONT fails or needs to be upgraded, the OLT can handle this without needing to visit the customer site. This makes OLT based PON networks very scalable and efficient to operate.