Network design and network build service. Project Management
Network cabling, Fibre optic solutions, Local area networks, Wide area networks
PON IMPLEMENTATION IN A SINGLE DWELLING UNIT AREA (SDU)
Tumai Fibre Networks Ltd offers a broad range of cable line equipment and possible solutions for FTTH/PON deployment outside of multi-dwelling unit areas (MDU). These may be urban areas with individual houses or suburban homes as well as rural communities. It should be noted that there is no alternative to technologies implementing the "Fiber-To-The-Home" principle (FTTH) for high-speed subscriber access to areas with individual dwellings.
Access via copper cables provides either insufficient speed (xDSL) or short transmission range (Ethernet + Category 5 twisted pair cable). The access technologies available via coaxial cables -- CATV networks (DOCSIS) -- often turn out to be expensive, especially when it is necessary to lay additional cables.
And finally, data transmission via copper conductors requires protection against overvoltage and overcurrent conditions, (pickups and failures in the power line, lightning, etc.), which is especially difficult with transmission speeds of 100 Mbit/s and higher.
SDU areas – specifics
The SDU areas can be conventionally divided into 2 categories by remoteness from the central office (communication service centre) of the operator.
Remoteness exceeding ~20 km/12.4 miles necessitates, as a rule, its own "active" node housing the active equipment. The main part of switching and distribution equipment (line and subscriber's optical distribution frames, splitters, etc.) of a standard "indoor" design is installed here, and external outdoor-design devices (cabinets, FTTH, etc.) are used to connect subscribers.
For the "near" zone (up to 20 km/12.4 miles from the operator's PoP), the possibility to omit an "active" node simplifies the construction task signifi- cantly and enhances the advantages of a PON. In this case, it is practical to locate the whole switching and distribution part of the network in the outdoor distribution devices.
The fundamental difference of PONs in the low-rise sector consists in the limited possibilities for location of the distribution network equipment in "public" spaces.
Distribution devices for all sectors of "rural" PONs must be delivered, as a rule, in an outdoor weatherproof design.
It should be also noted that the special-purpose cable ducts (wells, pipes, sewers etc.) may be absent in low-rise construction areas. In this case, the main method of cable laying is suspension of aerial cables on lighting or communication poles.
The FTTHs, distribution devices, etc. are also installed on these poles.
Splitting factor - selection
The active GPON equipment most commonly used in the market makes it possible, as a rule, to connect up to 128 subscribers to 1 OLT port.
Nevertheless, the use of the maximum splitting coefficient imposes strict constraints on the optical power budget and, finally, makes the operation of subscriber's devices impossible at a distance of more than 10 km/6.2 miles from OLT. On the other hand, at a distance between the operator and the subscriber exceeding 20 km/12.4 miles it is necessary to decrease the total splitting coefficient to 1x32 or less, which decreases the economic value of a PON.
Therefore, when designing the passive part of a GPON, splitting with a total coefficient of not more than 1x64 is most frequently used.
In order to decrease the capacity of distribution cables and the corresponding scope of works on optic fiber splicing, it is recommended to consider stage splitting.
For example, 1x16: 1x4 (i.e., 1x16 splitting at the first stage and 1x4 – at the second one), 1x8: 1x8 (1x8 splitting at the first and second stages), or 1х4:1х16 (1x4 splitting at the first stage and 1x16 – at the second one).
With this method, one fiber of a distribution cable serves not one subscriber, but a group according to the second stage splitting coefficient (4, 8, or 16, correspondingly).
Each splitting stage causes more than 1 dB of intrinsic losses in the line. The energy budget reserve in PON is low, of which the use of more than 2 splitting stages additionally limits the transmission range. With 3 and more stages there is a risk of not satisfying the specified leg - 20 km from the "town" (i.e. the operator).
To reduce the demand on the optical power budget, it is possible to use fusion splicing. At the same time, exclusion of detachable connections complicates the network administration significantly.
4 SUBSCRIBER CLUSTERS
GPON with 1x16 : 1x4 Splitting for group of 64 Subscribers