PLC Splitters Deployment Strategy—Cascaded or Centralized?

PLC splitters is commonly used fiber optic splitters of fiber optic networks such as FTTx (e.g. FTTH, Fiber to the Home) and PON (Passive Optical Network). In a PON system, the PLC splitter functions to share both cost and bandwidth of the OLT (Optical Line Terminal) among multiple ONTs (Optical Network Terminations) as well as reducing the fiber lines required in the OSP (outside plant). Depending on the customer distribution, there are two common deployment strategies of PLC splitters—Cascade and Centralized.

Cascaded Splitting

In the cascaded splitting model, the PLC splitters are located in the FDH (Fiber Distribution Hub) and at OSP locations, as shown in the picture below. Splitters in OSP, namely cascaded splitters, help minimize the amount of fiber that requires to be deployed to provide service, reducing distribution cable material costs. However, there are some disadvantages of this strategy. Because the cascaded splitters create inefficient use of OLT PON ports and increase the testing and turn-up time of customers.

PLC splitters -cascaded splitting

Advantage & Disadvantages Overview
Advantages Disadvantages
• Least Expensive Passive System to Design
— Minimal up-front network CAPEX requirements
— Uses Fiber-lean Feeder and Distribution System
• Limitations on Bandwidth and Adaptability
— No Single Splitter Configuration or Adaptation Point
— High splitting ratio may limit future network scalability and electronics
• Can be efficient
— Where Take Rate is High and Fairly Stable
— Where Growth is Not an Issue
• Inefficient where Take Rate is Low (<50%)
• Complex to Grow/Scale


Centralized Splitting

In the centralized splitting model, as its name suggested, all PLC splitters are centrally located in FDH locations (see the picture below). Using this deployment strategy, the OLT utilization can be maximized which provide a single point of access for troubleshooting. In addition to provide best OLT utilization & flexibility in limited take rate builds, the centralized splitting also provides easy craft access for testing and turn-up, as well as allowing for ease in transitioning to other PON technologies. But nothing is perfect. The cost of the centralized splitting is an increasing cost of distribution cable material.

PLC splitters -cascaded splitting

Advantage & Disadvantages Overview
Advantages Disadvantages
• LCP Consolidates Local Subscriber Configuration
—Ability to service 32 or more (typ. 64-500) Subscribers per PON
—Provides for a central turn-up location pointing to the OLT and ONT
• Requires Truck-Roll to FDH for Splitter Connection
—May increase cost of incremental subscriber turn-up
• Balances network scalability with up-front CAPEX
—Fiber-lean Feeder & Fiber-rich Distribution System
—Provides dedicated Optical Path from FDH to Subscribers
—Easily adaptable for future WDM PON and split ratio changes
• Supports Efficient Growth Strategies


Cascaded or Centralized?

Cascaded splitting strategy is an ideal option particularly when high take rates are certain or in extremely rural areas where fiber costs become more of a factor. Centralized splitting strategy that has its benefits including flexibility, ease of testing, and overall cost efficiency in many applications should be also considered. In a word, the best deployment strategy is the one that meets the requirements and expectations of the provider by reducing CAPEX, optimizing long-term OPEX, and making a future-proof network that can cope with new technologies without dramatic changes. This is why there are sometimes advantages to mixing both of them, creating a hybrid that leverages the advantages of each others.

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