Contents

	Welcome Note
	Cisco Partner
	The DSX Advantage
	FiberGuide
	FTTP Networks
	Bring your network out of the shadows

FTTX: Centralized Splitter approach in FTTP Networks

When a service provider considers the deployment of FTTP (Fibre to the Premises) architecture, the best option to offer multiple services to subscribers will be the one that is most cost effective, flexible and scalable. This part of FTTX article covers how to design a true FTTP solution considering the service providers need for operational flexibility and overall affordability.

One of the major considerations in building the fibre distribution portion of the network – the link between customer and central office is–which optical splitter approach will work best. Optical line terminal cards can service upto 32 customers today. Inefficient use of these expensive OLT cards will increase the initial deployment cost. Another important consideration to be made is the network’s ability to adapt newer technologies.

In a Passive Optical Network (PON) for FTTP, two common splitter configurations are the centralized and cascaded approaches. Centralized splitter approach typically uses a 1 X 32 splitter in an outside plan (OSP) enclosure such as a fibre distribution hub. In the case of a 1 X 32 splitter, each device is connected to an OLT in the central office. The 32 split fibres are routed directly from the optical splitter through distribution panels, splice points and / or access point connectors to the optical terminals at 32 homes. A cascaded splitter approach is normally configured with a 1X4 splitter residing in the OSP enclosure and connected directly to an OLT in the central office. Each of the four fibres leaving the 1X4 splitter is routed to an access terminal housing another splitter either a 1X4 or 1 X8. Eventually there will be 32 fibres reaching the ONT of 32 homes.

Out of the two splitter configurations, we recommend the centralized approach because of several advantages. Firstly, the centralized approach maximizes the highest efficiency of expensive OLT cards. Since each home in this approach is directly connected back to the central hub, there are no unused ports on the OLT card and 100% efficiency can be achieved. This approach also allows a much wider physical distribution of OLT ports. This aspect is very important when the initial take rates are projected to be low to moderate like what we can expect for the initial FTTP deployments being planned by some of the service providers in India. A cascaded splitter approach requires dedicating 32 fibres from a single 1X4 or 1X8 configuration back to the central office. This approach requires homes to be in the same physical vicinity because they must tap into access terminals that are linked together. If the service take rate is low, many of the fibres or ports will remain unused in this case. This approach will be good if the take rate is high.

Second major benefit of a centralized splitter approach is the ability to provide easy testing and trouble shooting access. It is very difficult to use an optical time domain reflectometer (OTDR) to test multiple splitters unless the network is built with each fibre characterized to enable the OTDR to recognize each individual fibre run. From a centralized point, it is nearly impossible to have visibility of individual fibre lengths through a series of splitters. A centralized splitter configuration on the other hand provides one centralized hub to trouble shoot instead of two or more.

Another advantage of centralized approach is the low signal loss. Each time an optical signal encounters a network component or connection (eg: splitter), it suffers a certain degree of signal loss. Therefore when splitters are cascaded together, loss will occur at each device. The combined loss effect can reduce the distance a signal can travel, imposing distance limitations on fibre runs. The centralized approach minimizes the signal loss by eliminating extra splices and connectors from the distribution network.

In summary, a cascaded splitter approach can make more sense in some applications, particularly when high take rates are certain or in extremely rural areas where fibre costs become more of a factor. However, careful consideration must be taken in light of the many benefits offered by a 1X32 centralized approach, particularly its flexibility, ease of testing and overall cost efficiencies in many applications.

This is an abstract from the book authored by ADC KRONE. ‘The book on FTTX: From Design to Deployment- A practical guide to FTTX Infrastructure’.

To read full article or know more about FTTX solutions visit: http://www.adc.com/productsandservices/productsolutions/fttp/