Which FO cable to install at each FTTH/FTTP deployment stage?
To connect subscribers to ultrafast broadband networks, telecom installers must build up and roll out reliable FTTH infrastructures by using very different FTTH solutions. Indeed, to link the different points of each network architecture between, whether take the form of a building, a street cabinet or an optical closure, FO cables specifically developed are required. We can distinguish three types of cabling systems that are mainly encountered in the deployment of FTTH networks in SDUs or MDUs, high-density or low-density areas:
- FTTH feeder cables: these cabling systems are used to connect the Central Office to one or various Fibre Distribution Hub(s). Deployed over distances of up to several kilometers, in overhead or underground layouts, optical feeder cables present a rugged construction and fairly large diameters. Depending on the density of the area to be covered, the fibre capacity of these optical cables is more or less high. Typically, for FTTH deployments including active equipment, FTTH feeder cables contain hundreds of fibres, whereas for deployments using passive equipment such as splitters, feeder cables are developed with a reduced fibre count.
- FTTH distribution cables: they are used to link a Fibre Concentration Hub - usually a street cabinet-, to an Optical Distribution Point which is a FTTH box. In a network configuration specific to a dense area, optical
distribution cables enable to bring the optical infrastructure as close as possible to the subscriber to be connected. The termination of FO distribution cables is performed inside a Building Entry Point (BEP – which is an optical
closure of generous dimensions) or at a few meters away from the house to be connected to the FTTH network.
- FTTH drop cables: these optical links are also called ʺindividual cablesʺ, as they connect the Optical Distribution Point (ODP) to the Optical Telecommunications Outlet (OTO) mounted at the subscriber’s premises. Drop cables are run over short distances, they present small diameters and enable thus easy and discreet installations. They are built with 1,2 or 4 fibre counts. Extremely flexible, optical drop cables enable the roll-out of the network in overhead layout, on facade, in duct or the visible cable laying inside dwellings.
Last mile connection: the FTTH cabling system from the ODP to the OTO
The last mile is a key stage for all FTTH deployments. Thanks to these last few meters of network, also known as the optical local loop, telecom operators will be able to guarantee better services than those provided with the use of FTTC (Fibre to the Curb) or FTTB (Fibre to the Building). Thus, to enable customer connection and depending on the network configuration, two types of cabling systems are to be implemented:
- The FTTH horizontal cabling. Used both for the connection of houses and buildings to very high-speed networks, horizontal cabling systems are available in a variety of cable constructions. According to the network topology, the horizontal cabling must meet various outdoor applications (overhead or underground layout and installation on façade) or indoor applications (cable running along walls and baseboards).
To enable FTTH connection in a SDU (Single Dwelling Unit), the optical horizontal cabling is the only type of cabling used for allowing access to ultrafast networks. Thus, from a ODP mounted on the top of a pole or on a facade, telecom installers run an aerial cable such as LX030PU up to an outdoor-indoor transition point where this FTTH outdoor drop cable will be connected to an indoor drop such as LM1L. For dual sheath cables such as LM4, this transition is not necessary and network can be deployed seamlessly as one single drop reference meets the needs of outdoor and indoor deployment. Inside the dwelling, the drop cable will end up in the FTTH socket where the telecom installer will perform fibre termination.
To enable FTTH connection in a building or a MDU (Multiple Dwelling Unit), the horizontal cabling will be supplemented with the optical vertical cabling. Thus, from an Optical Distribution Point located in a manhole or a pavement chamber, underground optical cables will be pulled up to the Building’s Entry Point. Inside this optical closure, the outdoor cable will be linked to the riser cable. Thanks to this last one, the FTTH network will be branched on each floor and subscriber premises will be reached with the use of an indoor drop cable.
- Optical vertical cabling. This type of FTTH cabling is only used for the FTTH roll-out in MDUs. The optical vertical cabling, also known as the riser cable, enable to link up two optical horizontal cabling parts. Thus, the riser cable is connected upstream to the outdoor distribution cable and downstream, to the indoor drop cabling. Fibre count is directly proportional to the number of potential subscribers. Indeed, to cut down CAPEX and OPEX by focusing on the deployment of a single infrastructure to be used in the long term, a riser must be sufficiently dimensioned to serve for the connection of all residents, if necessary.
Optical subscriber cable: quality guarantees long-term service
The optical subscriber cable or the optical subscriber link makes the connection between the optical outlet and the ONT (Optical Network Termination or the ISP box). Being the last part of the FTTH network, yet not the least, the subscriber FO cable is thus used to terminate the access network. Equipped with standard SC/APC connectors, this small optical cable plays an important role in the optical signal transmission. To reduce at most eventual negative impacts on the optical budget, it is important to select only quality FO subscriber cables, offering good performances in terms of bending radii, tensile strength, cut resistance, impact, crush resistance or resistance to duct friction. Indeed, even when routed in cable trays or ducts, and therefore protected, subscriber optical cables remain subject to various risks over a certain length. Hoovers, children playing nearby or accidental movements are some of the events that may cause immediate damage to your network.
For installation environments presenting a higher risk of damage such as office buildings, datacenters and industrial applications, there are steel armoured subscriber cables. These optical solutions present a metal armouring under the outer sheath which offers an increased protection to fibres and modules against mechanical stress, without however conceding to the cable flexibility.