FTTH - distribution methods in buildings

FTTH networks make an important part of modern telecommunication installations in residential buildings and other multi-dwelling units. The growing popularity of fiber optic systems "in the last mile" is the consequence both of legislation adopted in many countries and a growing awareness of investors. Nowadays, a fast and reliable access to the Internet and multimedia services has become a priority. The popularization of optical fibers is also possible due to cheap and effective technological solutions. Internet service providers have noticed the advantages of passive optical networks (xPON).
The designer of a fiber optic system for a specific building has to take into account several issues that have influence on the selection of cables and cabling techniques:
  • type of the building - office building, residential building etc.
  • system topology, including the locations of cable shafts
  • system applications, connected with the technology and kind of services
  • network utilization factor - connection of all outlets or subsequent connections of new users
Given these factors, it is possible to select the appropriate cabling technique. There are four popular methods:

1 - indoor "breakout" and subscriber cables
2 - cabling based on micro-tubes
3 - cabling based on easy access cables
4 - cabling in a star topology, based on subscriber cables
Breakout cables
The method based on the breakout distribution cables resembles that known from cable TV distribution systems. The cables are run from the optical distribution frame located in the bottom of the building to all or selected floors, where they are connected to subscribers cables terminated with outlets. The number of fibers in each cable is the same as the number of outlets on the corresponding floor. The cable on a given floor enters the distribution box where the fibers are spliced with the fibers of the subscriber cables. The fibers of the subscriber cables should be characterized by reduced bending radius.
Optical Fiber Distribution Frame: ULTIMODE TB-48B (wall-mounted)
FTTH solution based on breakout distribution cables

This cabling method is the most universal and can be applied in almost any building, regardless of its type and layout/topology. Compared with methods presented in the further parts, it involves implementation of the entire system at the installation stage. Not without significance is also the need for the distribution box on each floor.
The second technique is especially useful in the case when the number of subscribers / outlets is not known in advance.

Cabling system based on micro-tubes or microducts consists of specially designed packages of small flexible tubes. Each single tube is provided to to the potential subscriber. It is also possible to connect individual packets of horizontal tubes in the duct using special connectors. Commercially available solutions offer a number of opportunities in the selection of the structure both of the packages and individual micro-tubes. They can vary in shape, dimensions, flexibility and color.
The structure of a cabling system based on micro-tubes
Both of the packages and individual micro-tubes can vary in shape, dimensions, flexibility and color
(source: ftthcouncil.eu)
The fibers are usually blown into the microducts implemented in the building with the use of blowing-in machines (the source of the picture: ftthcouncil.eu). The process is easy and quick. With this approach, the operator does not bear the costs associated with unused links - the fibers are provided only to the actual subscribers.
Easy access cables
The third FTTH technology, in a sense combining the two approaches described earlier, is the implementation of the cabling based on so-called "easy access cables". This method seems to be the most versatile and flexible way to bring fiber to apartments in multifamily buildings.
1. Window cut marker on the sheath
2. Loose central tube with fibers
3. Aramid rod
4. LSZH sheath
5. 900 μm tight buffer fiber
The structure of an easy access cable
Easy access cable is a fiber optic cable consisting of multiple fibers (e.g. 12, 24, 36 or 48) with 0.9 mm tight buffer coatings, located in LSZH tube. The fibers can be branched directly to individual subscribers without the need for splicing within the riser of the building. They are easily extracted from breaking windows in the gel-free tube. The breaking windows are protected by breakout units, the branch fibers are pulled out of the cable and conducted inside protective tubes to the subscribers' outlets. Any installation work connected with pulling out fibers can be carried out only after unwinding the cable reserve from the rack that is usually placed on the top floor of the building.
The installation of the cabling can be done in stages, first of the cable in the riser(s), then of the protective tubes, and finally - the pulling out of the fibers for selected apartments and splicing them with pigtails.
More information on easy access cable: "Fiber optics in homes in a few simple steps", as well as in the video below (so far with Polish soundtrack).
Subscriber cables in a star topology
In this method, a separate indoor distribution cable e.g. ULTIMODE ILB-2SM-A L7102 goes from the technical room to each apartment or business premises. The method is popular due to low price of such distribution cables and a minimal cost of the necessary tools. In the case of many terminal outlets, the installer can have problems with proper arrangement of multiple cables in the distribution frame (to preserve the minimum bending radius for each cable/fiber).
In the FTTH - installation of a distribution frame/box article we provide more information about this method, including an example of implementation of 1U RACK distribution frame with comments on installation and splicing procedures.