Understanding FTTH infrastructures for optimising subscribers’ connections

FTTH is a network architecture consisting of deploying fiber optics from the Point of Presence (PoP) to the subscriber’s premises, whether home or business. The PoP can take the appearance of a building or a street cabinet hosting the active equipment of telecom operators. Upstream, the PoP is connected to a wider distribution layer such as the urban or metropolitan network. Downstream, it enables to cover a neighborhood or a residential/industrial area. As a strategic point that demarcates the local loop from the distribution network, the PoP is located nearby a SCN (Subscriber Connection Node, equivalent of PoP for the copper networks) and at an optimal distance from the subscribers to be connected ( at the core of a neighbourhood, at the entry of a residential area etc.). From this PoP, the local loop or the acess network organizes around three network sections:


full fibre customer connections ensure the best Internet speed rates and 3play services

  • A horizontal optical network that crisscrosses the streets and terminates at the entry of a building (MDU), an individual house (SDU) or a commercial premises. On site, this network is materialized by aerial or underground drop cables and optical distribution closures such as Optical Distribution Points.

  • A vertical optical network for MDU roll-outs. This network fragment is built thanks to a riser cable that carries the optical signal from the Building Entry Point to all floors so to subsequently connect up to 144 subscribers.

  • Last few meters (final hook up). This last section includes indoor drop cables that link, depending on the network configuration, a Building Entry Point to a subscriber terminal socket or an optical box such as a transition box to the FTTH outlet.


Fiber-to-the-Home stands out among the other FTTx network architectures (lien cocon 2) as in this case, fiber optic is the only technology implemented throughout the network. By removing the mix between the technological solutions, telecom operators are able to provide more stable and reliable networks with higher speed rates.

PON and Ethernet : two network configurations for connecting subscribers directly to fiber


Throughout the world, two distinct network configurations enable the deployment of fiber up to the subscriber : the PON and the Ethernet.


  • In the case of PON technology, optical cables leaving the PoP are routed to a Concentration Point located nearby the premises to be connected, generally materialized by a street cabinet. At the level of this fiber optic Concentration Point, a splitter is then used to share the bandwidth contained in a single fiber until then between 64 or 128 subscribers pending connection. Thus, a single PON interface will be available for all the premises to be connected. This configuration is also known as Point to Multipoint (P2MP) and is widely spread and adopted by network installers due to its attractive cost/benefit ratio. Furthermore, the place where the splitter is located plays a major role in the optimization of a PON network : it determines the needs in terms of network equipment to be installed, notably of fiber and optical distribution boxes.

  • In the case of Ethernet configuration, fiber optic leaving the PoP is directly routed to the subscriber’s premises. This type of network is also known as a Point-to-Point (P2P) architecture. It allows a FTTH network to be deployed in a straightforward, linear and simplified manner. The biggest advantage of this configuration is that the Ethernet network allows telecom operators and ISPs to guarantee the highest speed rates as the bandwidth is transmitted directly from the PoP to the subscriber’s terminal outlet. By contrast, an Ethernet network implies greater needs in terms of fiber solution supplies.

fibre optics can be deployed from the Central Office to customer premises by using the PON or Ethernet technology

The choice between a network configuration and another has a direct impact on the deployment cost and the network equipment requirements. Also, in accordance with the demographic concentration, the segmentation of the premises to be connected, the fiber counts to be provided per premises, different solutions will be retained. To ensure the success of an FTTH project deployment, it is recommended to adapt the performance of FTTH cabling systems and fiber optic closures to the network topology requirements, and more generally, to the installation environment.

ODP, transition box, FTTH socket: how to adapt the passive equipment to the network configuration


The success of a FTTH roll-out depends on a number of various factors. For instance, the infrastructure of an access network can be deployed both in public and private space. In order for interventions on site to be performed, a certain number of authorisations must be obtained in advance. Furthermore, to ensure a good return on investment, it is essential to select network equipment that matches the network configuration. The cabling system, optical distribution points, all the required equipment must be qualified for the given installation requirements. Here are some analysis criteria that may help you putting your FTTH roll-out project in perspective:

Consideration criteria

Associated constraint(s)

Example of FTTH solutions

High density area / Low Density Area

According to the number of the subscribers to be connected to the very high-speed networks, different FTTH solutions are emerging and are to be implemented.

  • High density area: Building Entry Point, Floor Distribution Box, LM1L, OTO for MDUs connections

  • Low density area: PBO S2 and S1 / PBO G, LM2 / LX030PU, DTIO, LM1L, OTO


The fiber counts to be foreseen in the construction of distribution and drop cables, as well as the number of cables to be accommodated inside the optical boxes are directly proportional to the total of subscribers to be connected.

  • MDU: Building Entry Point for cable storage, riser cable, Floor Distribution Box, LM1 / LM1L, OTO

  • SDU: PBO / PBO G, LX030PU, fiber optic transition box / DTIO, LM1L, OTO

Brownfield / Greenfield / Overbuild

In the case of Brownfield or Greenfield constructions, FTTH roll-outs are usually performed by using the underground infrastructure foreseen for this purpose. By contrast, for Overbuild or ancient housings, fiber optic is commonly deployed in overhead layouts. Therefore, the choice of a cabling solution will depend on the level of congestion of available conduits or ducts.

  • Brownfield or Greenfield: PBO G, LM2 / LM4 / LM7, fiber optic transition box, LM1L, OTO

  • Overbuild: PBO/PBO G, fiber transition box / DTIO, LM1L/ LM7, OTO

Overhead / Underground configuration

Both FTTH cables and fiber optic boxes installed in one of these two configurations must be qualified and present specific performance requirements. For an overhead roll-out, wind and eventual additional loads such as frost or snow must be taken into account when choosing the cabling solution, as this later one must withstand all these variables. In the case of an underground installation, network equipment must be selected by considering its performances in terms of resistance to moisture.

  • Overhead configuration: Pre-terminated or for fusion splicing Optical Distribution Point S1 and/or S2, LX030PU/LM4, fiber transition box/DTIO, LM1/LM1L, OTO

  • Underground configuration: PBO G, DTIO/fiber optic transition box, LM1 /LM1L, OTO

Country (specificity of the territory, regulatory framework, uses etc.)

Each country has its own regulatory framework as well as its specific practices when it comes to fiber optic deployment. For some territories, shared networks are a standard, while others focus on unbundling.

  • France : ARCEP, incumbent - Orange

  • UK : Openreach, PIA, incumbent - British Telecom

  • Germany : RegTP, incumbent - Deutsche Telekom

  • Mexico : CFE, incumbent -Telmex

Installation environnement (weather conditions)

Some territories are more exposed than others to difficult weather conditions. In coastal areas, as for instance, strong winds can affect the quality of the optical signal if the cabling system has not been designed for such applications. Also, in mountainous areas, the risk of snow, rock fall as well as the formation of frost are some of the factors to be considered when choosing the network equipment to be installed for building a FTTH network.

  • Coastal area: LX030PU especially designed to offer good wind performance

  • Damp climate: pole line hardware and passive network equipment in stainless steel, resistant to the atmospheric corrosion; watertight optical distribution boxes such as PBO or PBO G

  • High temperatures: UV resistant cabling such as LM4 (thermal cycling -40°C to +70°C) or Droptic® LX030PU (-20°C to +60°C) ; high performance thermoplastic FO closures such as the Optical Distribution Point (operating temperature 40°C to 65°C)