Choosing a type of fiber is critical in designing network, either single-mode or multi-mode. Guiding Principles are affecting decision, since scalability and future proofing should be considered.
Single fiber mode is compatible with existing fiber deployments and hardware solutions, making vendors keep pricing low and provide multiple variations. In practice the carrying capacity of single-mode fiber is larger than multi-mode fiber. If it would be possible to couple all of the modes of a multi-mode fiber across a broad spectrum, the choice would be multi-mode. Lower cost is one of the driving forces for single-mode fiber deployment. Despite the higher prices of lasers and connectors used in single-mode fiber and lower prices of LEDs that are used for multi-mode it is cheaper to deploy single-mode due to larger speed and longer range. While multi-mode is acceptable for intrabuilding connection, single-mode fiber can have greater link lengths and higher bit rates making it more cost effective for long range designs. There are three main types of single-mode fiber commonly used: lower water peak loss fiber, non-zero dispersion fiber, and large effective aperture fiber. Last two types of fiber have been developed for very long distances, up to 3000 km. FTTH is using relatively short distances, so use of fibers that reduce the amount of water in the fiber makes more sense.
After the type of fiber has been chosen, designer of the network should decide, where the equipment should be deployed. Fiber coming out of the “customer” will be terminated at the local OLT, which should be located somewhere between the CO and customer. Installation of OLT as close as possible to customer would save some money on fiber, but it would result in some scalability issues. In real life scenario, it is expected that network will grow and new services would be introduced, which would increase the overall per subscriber electronics cost.