Passive optical network
A single fibre optic is run to a passive optical splitter from the OLT at the provider’s central office or PoP. The splitter replicates and divides the light signal, relaying it to many ONTs near end users. Typically, the signal is split between 32 ONTs, although the latest PON standards support 64 or more.
The ONTs then provide the signal to end users. Depending on where the PON ends, this can be:
- Fibre to the premises (FTTP): The fibre connection runs all the way to a customer’s home or business.
- Fibre to the building (FTTB): The fibre cabling runs to the building, for example, serving an apartment block, school or office block.
- Fibre to the cabinet (FTTC): The fire cabling runs to a curbside cabinet, where it’s distributed to individual homes and businesses via copper wires.
- Fibre to the neighbourhood (FTTN): The fibre may end a few miles from the customer’s premises.
Since a PON uses a single fibre, it typically uses wavelength-division multiplexing to split the light signal into upstream and downstream channels. Downstream, the signal is visible to all ONTs. However, each ONT only reads the data addressed to it, and encryption is used to stop eavesdropping on adjacent channels.
Upstream, the wavelength is typically divided by time-division multiplexing, meaning each ONT takes turns transmitting with time slots assigned by the OLT.
With the fibre signal powered only by the OLT, the latest PONs can cover distances of 20-40 km (12-24 miles) between the OLT and the end user.
What are the advantages of passive optical networks?
The passive nature of PONs gives them several advantages over active optical networks:
- Lower costs: PONs are simpler, with fewer components, unpowered splitters and fewer fibre cables, so they tend to cost less to deploy and maintain.
- Energy efficiency: PONs are more energy efficient than active networks because they don’t require power to run and cool active components.
- Reliability: As PONs use fewer passive optical components, which are less prone to failure than powered switching equipment, PONs tend to be more reliable.
- Scalability: PONs are easy to scale by adding more optical network terminals (ONTs), while active networks are more likely to require infrastructure upgrades as they expand.
Types of passive optical networks
Originally developed in the 1990s, the first passive optical networks used Asynchronous Transfer Mode (ATM) to distribute the light signal. APON (ATM PON), which quickly evolved into BPON (Broadband PON), typically delivers data transfer speeds of up to 622Mbps downstream and 155Mbps downstream.
Over the last two decades, GPON and EPON emerged as the main PON standards, although these are fast being superseded by next-generation standards.
GPON
First ratified by the ITU-T in 2003, Gigabit PON (GPON) uses a mixture of ATM and ethernet technology protocols and typically provides speeds of 2.5Gbps downstream and 1.25Mbps upstream. GPON is currently one of the most widely deployed PON standards.
EPON
An alternative protocol ratified by the IEEE in 2004, Ethernet PON (EPON) uses ethernet as its transport protocol and typically provides the same upstream and downstream speeds -- up to 1.25Gbps. Network providers sometimes choose EPON because it works seamlessly with ethernet-based networks and services.
Later-generation PON standards, like XGS-PON and 10G-EPON, can deliver speeds of 10Gbps, while next-generation protocols, like NG-PON2, are set to achieve speeds of up to 40Gbps or more.
Deploying passive optical networks
As UK businesses look to invest in digital transformation, internet service providers are using passive optical networks to give businesses the high-capacity, gigabit-enabled networks they need.
At Neos Networks, we’re helping businesses build their digital future across the UK. To find out more about options for deploying optical connectivity, get in touch.
