A Passive Optical Network (PON) works by using a single optical fiber to serve multiple endpoints, relying on passive optical splitters to distribute the signal. Here's a breakdown:
1. The Head End: Optical Line Terminal (OLT)
- The OLT sits at the service provider's central office. It's the starting point of the PON and acts as the "brain" of the network.
- The OLT manages traffic to and from all the Optical Network Terminals (ONTs).
- It converts electrical signals to optical signals for downstream transmission and vice-versa for upstream reception.
2. The Fiber Optic Cable
- A single fiber optic cable runs from the OLT out into the distribution network. Fiber optic cables use light to transmit data, allowing for very high bandwidth and long distances.
3. The Passive Optical Splitter
- This is a key component. The splitter is a passive device, meaning it requires no electrical power.
- Its function is to take the optical signal from the OLT and duplicate it, sending it to multiple ONTs. Common split ratios are 1:32 or 1:64, meaning one fiber from the OLT can serve 32 or 64 ONTs, respectively.
- Splitters use prisms and mirrors to physically divide the light signal.
4. The Endpoints: Optical Network Terminals (ONTs)
- The ONT is located at the customer's premises (home or business). It is sometimes also called an Optical Network Unit (ONU).
- The ONT converts the optical signal back into an electrical signal that can be used by the customer's devices (computers, routers, phones, etc.).
- In the downstream direction, each ONT receives the same signal from the OLT (after the splitter). The ONT then filters out the data intended for it.
- In the upstream direction (from ONT to OLT), a technique called Time Division Multiple Access (TDMA) is used. This means that each ONT is assigned a specific time slot to transmit data, preventing collisions on the shared fiber. This ensures that all ONTs can send data back to the OLT without interfering with each other.
In Summary:
| Component | Location | Function |
|---|---|---|
| Optical Line Terminal (OLT) | Service Provider's Central Office | Central control point; converts electrical signals to optical and vice-versa; manages data flow. |
| Fiber Optic Cable | Between OLT and Splitter(s)/ONTs | Transports optical signals. |
| Optical Splitter | Between OLT and ONTs | Passively divides the optical signal to multiple ONTs. Requires no power. |
| Optical Network Terminal (ONT) | Customer Premises (Home or Business) | Converts optical signals to electrical; provides connectivity to customer devices; transmits data upstream to OLT via TDMA. |
Advantages of PON:
- Cost-Effective: Sharing a single fiber optic cable among multiple users significantly reduces infrastructure costs.
- High Bandwidth: Fiber optics provide very high bandwidth capabilities.
- Passive Infrastructure: The absence of active components (requiring power) in the distribution network reduces maintenance costs and improves reliability.
