FTTH Network Design and Implementation

FTTH Network Design Details: The optical fiber is the most advanced transmission medium in telecom sectors and the only one transmission medium is capable of supporting next generation services. The main advantages of having a last mile of optical fiber network are many like higher the bandwidth, longer distances from the central to the subscriber end, optical fiber is the the more resistance to electromagnetic interference, increased security, reduced the signal degradation in the transmission. In-fact FTTH networks are based on Point to multi-point types configuration. FTTH technology involves the introduction of fiber optic in the global network, both the backbone network operator as the last mile.

Here I would like to write about the FTTH trench dimensions,duct size,duct colors etc. Below I have mentioned in details step by step. FTTH optical network specifically a link between the central node and the end user customers. It is also very important to know about the below details. 

Trench Dimensions Duct Size In FTTH Network Design:-

Feeder Routes (Exchange To FDT):-

Trench: 200 mm width, 600 depth from Asphalt / 500 mm from GL.

Ducts: - For Streets wider than 30 m: 20x32 mm dia. + 16x20 mm dia.

- For Streets less than 30 m: 16x32 mm dia. + 16x20 mm dia.

Colors: Black ; Orange; and Orange with Black Stripes )

Distribution Routes (FDT To FAT):-

Trench: 200 mm width, 600 depth from Asphalt / 500 mm from GL.

Ducts: 12x32 mm dia. + 25x20 mm dia.

Colors: Black (6); Orange (3); and Orange with Black Stripes

Distribution Routes (FAT To Client):-

Trench: 130 mm width, 500 depth from Asphalt / 400 mm from

GL.Ducts: 25x20 mm dia.
&

Drops To Houses:-

Trench: 130 mm width, 500 depth from Asphalt / 400 mm from GL.

Ducts: 2x20 mm dia.

Length of duct Not more than 300 meters from FAT

Drops To Houses:-

Blown Fiber

Trench: 130 mm width, 500 depth from Asphalt / 400 mm from GL.

Ducts: 2x2X14 mm dia. Or 50 mm duct with 4x14 mm micro ducts.

Manhole (MH)

Manhole used with small trenching is the Mini Manhole

Dimensions :1200x1200x1500 mm (ID)

Openings in Mini MH Walls: (On Sides in line withthe streets)

•20x35 mm dia. (for 32 mm ducts)

•16x25 mm dia. (for 20 mm ducts)

FTTH NETWORK SPLITTING LEVEL:-

In Passive Optical Network (PON), optical splitters play an important role in Fiber to the Home (FTTH) networks by allowing a single PON interface to be shared among many subscribers. Optical Splitters are installed in each optical network between the PON Optical Line Terminal (OLT) and the Optical Network Terminals (ONTs) that the OLT serves. During the deployment of fiber to the home passive optical network, usually, we will face some physical access network design problems. This article may help you solve FTTH splitting lever and ratio design problems.

FTTH Network

FTTH Network Splitting Level

FTTH Splitter

Generic operation of optical splitter

One of the best way to expressed the operation of a splitter with the above figure, you can understood easily about the FTTH splitter with the help of above figure.

Choose PLC Splitter or FBT Splitter?

Before we start to discuss the splitting lever and ration design,it’s necessary to choose the right optical splitter type for the FTTH network. There are two types of splitters in our current FTTH application—PLC splitter and FBT splitter. Here we have

 Comparison between these two splitter types:

Splitter type

Parameters	PLC Splitter	FBT Splitter
Wavelength Range	1260-1650 nm	Single/dual/triple window
Splitting Ratio	Equal division	Equal or non-equal division
Dimensions	Small	Large size for multi-channel
Wavelength Sensitivity	Low	High
Cost	Low splitting channel, high price	Price is lower for small channel spliter

As we can see in the above mentioned table that with the fast growth of FTTH worldwide, the requirement for larger split configurations (1×32, 1×64, etc) in these networks has also grown in big order to serve mass subscribers, PLC splitters offer very accurate and even splits with minimal loss in an efficient package in transmission, it can offer a better solution for today’s telecom network for the FTTH applications than FBT splitters.

FTTH Network Splitting Level Design

The Passive Optical Network (PON) is the optical fiber infrastructure of  FTTH network. The first crucial point is the architectural decision for the Passive Optical Network (PON) is that of optical splitter placement according to customer demand. The Passive Optical Network (PON) splitting may be achieved by centralized splitting (one-level) or by cascaded splittings (two-level or more). A centralized approach typically uses the splitter 1×32 and it is located in a fiber distribution hub (FDH). The splitter is directly connected through a single fiber to a OLT in the central office of the telecom operators. On the other side of the splitter, 32 fibers are provided to 32 customers’ homes, where it is connected to an Optical line terminal (ONT). Thus, the Passive Optical Network (PON) connects one OLT port to 32 ONTs.

FTTH Network

FTTH Network Splitting 

It is important to note that a cascaded approach may use a 1×4 splitter residing in an outside plant enclosure. This is directly connected to an Optical Line Termina (OLT) port in the central office of the telecom operators.Each of the four optical fibers leaving this lever-1 splitter is provided to an access terminal that houses to a 1×8 level-2 splitter. In this scenario, there would be a also total of 32 optical fibers (4×8) reaching 32 homes customers. This is possible to have more than two splitting levels in a cascaded system, and the overall split ratio may vary (1×16 = 4×4, 1×32 = 4×8, 1×64 = 4x4x4).

FTTH Network Splitter

A centralized architecture of FTTH Network typically offers greater flexibility, minimized  operational costs and easy to access for the technicians. A cascaded systems approach may yield a faster return-on-investment with lower first-in and optical fiber costs. Usually, the centralized splitting solution is used in crowded metro city center or town areas, in order to reduce cost of network and easy to maintain the optical distributed network (ODN) nodes. In the other hand, two-level and multi-level cascaded splitting solution is used in small town or village places, to cover widely ODN nodes of the FTTH network, conserve resources and save the money.

FTTH Network Splitting Ratio Design

The most common splitters used in a passive optical network (PON) system is a uniform power splitter with a 1:N or 2:N splitting ratio (N=2~64), where N used for the number of output ports. The optical fiber input power is distributed uniformly across all the output ports. Different ratio splitters may perform differently in the FTTH network. Then,question is very important that how to design your splitting ratio? 

According to the mentioned above, if the telecom operators choose the centralized splitting solution, it may need to use 1×32 or 1×64 splitter. However, if telecom operators choose the cascaded splitting solution, 1×4 and 1×8 splitter may be used more often. Besides, based on FTTH system EPON/GPON project experience, when the splitting ratio is 1:32, implemented network can receive qualified fiber optic signal in 20 km. If the distance between OLT and ONU is small, suppose in 5 km, it can also consider about 1:64.

FTTH Network Splitter

Conclusion

When to design the FTTH network splitting level, in fact, centralized splitting and cascaded splitting both has its advantages and disadvantages, suitable action can be taken by telecom operators.Telecom operators had to weight these factors and select an appropriate splitting level for the FTTH network. As for splitting ratio design, it is important to ensure a reliable signal transmission, the longer the transmission distance, the lower splitting ratio should be used.