Fibre getting the better of coaxial

FTTx is the all-inclusive term that covers a number of possibilities for fibre-optic networking. Fibre to the home (FTTH) is probably the first one that comes to most people’s minds. It is also called fibre to the premises and fibre to the building. Terms less often heard are FTTN and FTTC.

The entire FTTx system starts at the headend, which belongs to service providers.

Fibre is usually part of the service provider’s network, particularly in areas of newly constructed neighbourhoods.

In older cities, more of the backbone structure tends to be coaxial cable and today, especially in the US, some service providers are replacing the coax with fibre.

FTTH is an ideal situation, as it provides the greatest bandwidth and speed to the user and brings the fibre from the headend to a network interface box on the side of a home, apartment complex or office building.

At this point, the signal is usually converted to an RF signal for distribution within the structure. This is accomplished with a micro-node.

The distribution of the signal in a home or building can also be accomplished with fibre optics. One US company has a plastic optical cable system, that can distribute the fibre signal.

The system works using an active optical system over duplex fibre cable.

The conversion of the signal from light to electrical is accomplished in the connectors that have a receiver and transmitter built into each side of the connector.

The system takes the RF signal from a cable modem, converts it to light, transmits it to the cable box on a TV, for example, and then converts it back to an RF signal. The system can transmit signals up to 100 m at speeds up to 250 Mbps.

The connectors in the system are standard RJ45s on the electrical side and custom POF connectors on the optical side. Connecting is simple. It just requires cutting and stripping the duplex cable and then inserting the fibres into the connector.

The alignment of the fibre is accomplished through alignment features in the connector and the active LED components. No fibre polishing is required.

FTTH solutions can be direct or shared fibre. Direct is a single fibre running from the headend to the home. It has the best performance.

Shared is a single fibre running from the headend to a node in a neighbourhood, where it is then split and delivered to individual users.

It is the most common system, but the signals are multiplexed and encrypted so each user’s information is secure.

FTTH solutions can also be active or passive optical networks.

Active networks require passing the signal from the headend through electrically powered equipment that can amplify the signal and direct it using IP switching/routing.

A passive network is light only from the headend. The signal is physically divided off to individual users by splitters and protected by encryption. A passive optical splitter can be capable of splitting the light signal into 64 separate signals.

Termination of the individual fibre is through splicing. An ADC passive optical splitter module can split a light signal into 32 separate signals for each module installed in a rack or cabinet.

These fibres are pre-terminated with connectors for easier installation.

Fibre to the node (FTTN) and fibre to the kerb (FTTC) both refer to optical cable being run into a neighbourhood on optic cable, where it is terminated in a cabinet on the street.

In FTTH, the light signal will be passed on to the homes in the neighbourhood. In many systems, particularly in older neighbourhoods, the signal is converted to an RF signal over coax cable or, with a phone service, is converted to a DSL signal over twisted-pair wires, which is then connected to each home.

The signal is then converted to IP by the cable or DSL modem.

FTTH is still in its infancy.

For those in rural areas, it is likely that the systems will never be deployed, due to the high cost per subscriber.

Besides standard phone lines, most rural customers that want high-speed internet service will have to opt for the relatively lower-cost satellite services.

Robin Pearce, Bishop & Associates

rpearce@bishopinc.com