How to choose a FTTH outdoor drop cable?
The FTTH drop cables are used to enable subscriber connections by linking the Optical Distribution Point to the Optical Telecommunications Outlet. Depending on their application, these optical cables are classified into three main categories: outdoor, indoor and outdor-indoor drops. Thus, depending on where they are used within the FTTH infrastructure, optical drop cables must meet a number of performance criteria.
Unlike indoor drops, which are submitted to very few stress after installation, outdoor drop cables must withstand a wide variety of constraints. These optical cables are telecom cables strung alongside telephone poles, used for underground roll-outs and installations into ducts or simply laid or extended alongside facades.
To make the right choice in terms of FTTH cabling solution for your network roll-out, it is important to consider:
- the most demanding weather conditions for the area where the cable is to be installed. For instance, an aerial cable deployed in an urban sector will not be subject to the same stress as an overhead line installed in a mountain area where snow, frost, falling rocks or hunting accident represent potentiel risks for the network’s integrity
- mechanical stress associated with the cable installation in a given geographical area
How to choose the right aerial optical cable for the roll-out of access networks?
For economic reasons, fiber optic deployments in rural areas usually use the existing overhead infrastructures (telephone our utility poles). Thus, to bring fiber to the premises into uncovered areas and to bridge the digital divide or to connect individual or multiple dwellings where underground infrastructure is absent or unexploitable, overhead drop cables are the most suitable FTTH solutions. However, these outdoor cables must meet a number of criteria so to ensure an optimal transmission of the optical signal :
- present a rugged construction
- UV resistant
- resistance to temperature variations
- offering mechanical performances adapted to the installation environement and the associated conditions
While the first three selection criteria can be easily verified by paying close attention to the technical specifications provided by the cable manufacturer, the assessment of mechanical performances can sometimes turn into a rather complex matter. To simplify at most, here are the main characteristics that deserve close consideration:
- the tensile strength: to ensure an effective and reliable cable installation
- the cable’s structure: while for optical cables with loose tube structure the fiber is isolated from outer mechanical stress by the tube itself or by a tube filled with gel, cables presenting a tight or semi-tight structure offer a higher resistance to impact or crush
- the cable’s weight: a lightweight cable will exert little mechanical stress on telephone or utility poles. This is also available in case of frost where it is useful to note that the cable span load distributed between the two poles will be increased by an additional weight
- the wind resistance: for fiber roll-outs in coastal areas for example, between two drop cables offering almost equal performances such as the Droptic® LX030PU and the Droptic® LX048DS, it is recommended to choose the FTTH cable with the smallest diameter, as it will provide for a better wind resistance
- the bending: the indicated value must be respected for the installation of the cable in overhead configuration, as well as for the association with compatible dead-ending and suspension clamps
- the kink: a cable’s capacity to resist or recover after being subject to a given compressive force
Which drop cable for un underground fiber deployment?
Where possible, the roll-out of FTTH networks is also performed by using the available underground infrastructure. This is mainly the case for subscriber connections in urban areas where, for aesthetic reasons but also to avoid the risk of pulling out overhead cables, access networks are deployed inside ducts. To ensure compatibility between the chosen drop cable and its installation into duct, it is essential to verify :
- that its tensile strength allows an installation without risk of breakage or impact on the quality of the optical signal
- for an installation into an occupied or congested duct : that the cable’s diameter is small enough to pass through the duct and its construction is both flexible yet rigid so to ensure effective cable installation
- that the used optical cable is a watertight drop cable. Thus, to prevent any risk of optical loss caused by a prolonged exposure of the cable to water, it is important to check if the underground optical cable presents swelling yarns in its construction
In the eventuality where several drop cables offer watertight constructions such as Droptic® LM4, LM2 or LM8, it is then recommended to make an informed choice by considering the length of the network section to be build. Thus, while the LM4 drop cable is engineered for being pulled into ducts on several hundred meters, the LM2 and LM8 drops can only be installed on distances of up to 50 meters.
Building FTTH access networks on facade
Outdoor drop cables can also be installed on front facades : they can be strung or laid alongside exterior walls. Irrespective of the installation technique on the facade, these optical cables must present an UV resistant outer sheath. In order to ensure optimal optical transmission at all times, it is recommended to opt for outdoor drop cables offering a wide operating temperature range. This will prevent network failure risks due to climatic variations.
Finally, for a FTTH roll-out on facade it is preferable to choose outdoor drop cables with reduced dimensions. Indeed, the smaller the cable diameter, the less the installation will be visible. However, before selecting by default the outdoor drop with the smallest diameter, it is important to take into account its bending value so to make sure that this can be strictly respected during the cable installation.
If each application requires a certain type of drop cable, Telenco networks goes further. The company provides full ranges of drop cables especially developed to meet where possible all network configurations’ needs. Thus, in the Droptic® catalogue you will find outdoor drop cables engineered to adapt as well to an installation into ducts, overhead layout or installation on facade.