Optical Fibre for FTTH Deployment

A number of different optical fibre types are available (see Appendix I). The majority of FTTH schemes are likely to be based on single-mode fibre, but multimode fibre may also be used in specific situations. The choice of fibre will depend on a number of considerations. Those listed below are not exhaustive and other factors may need to be considered on a case-by-case basis.

Network Architecture Type
The network architecture options are covered by a separate document. This largely affects the amount and control (flexibility) of bandwidth fed to each subscriber.

Size of the FTTH network
The size of the FTTH network covers the numbers of house/apartments in the FTTH area. This is a measure of subscriber density and largely affects fibre counts within the network. The FTTH site may be a new greenfield type or a site requiring an overbuild of the existing communications network.

Location of the FTTH network to existing feeding fibre network
When siting a new FTTH network, care must be exercised regarding its position with respect to the existing or serving metropolitan/urban fibre network, or local access fibre network. Particularly, the overall optical distance that will need to be covered between the transmission equipment needs to be considered as this affects the fibre attenuation and bandwidth carrying capacity.

The Existing Network Fibre Type
The Existing Network Fibre Type is most likely to be single-mode fibre and this will link back to the Access Node (or POP) to the serving equipment. A fibre connection link to the FTTH network area will be required from a strategic point in the network (fibre concentration point).

Expected lifetime and future upgrade
The FTTH network lifetime could be 30 years or more. Therefore, it is imperative that any investment made in the FTTH infrastructure is able to serve future needs as well as those of today. Changing the fibre type halfway through the expected lifetime of the FTTH network is not a desirable option.

Single-mode fibre
Single-mode fibre offers the lowest optical loss (best distance) and highest bandwidth carrying capacity. Since it is the most widely used fibre, particularly further back in the network, it is likely to be the same and therefore compatible with the existing legacy fibre base. Thus any connection to a new FTTH network will be transparent (no additional active equipment) and uniform (common practices, tools and maintenance). It also offers the greatest potential for future upgrade, using higher-level active equipment to exploit its huge bandwidth-carrying capacity.
Single-mode fibre is the lowest cost fibre option but incurs higher equipment costs compared with multimode fibre systems. For the future, wide scale FTTH deployments may reduce single-mode equipment costs through increased volumes.

Multimode fibre
Multimode fibre is generally accepted as a solution for in-building and campus data networks. It has lower equipment and connection costs but higher fibre costs compared to single-mode fibre. It provides lower bandwidth carrying capacity compared to single mode fibre, although newer types of fibre (refer to Appendix 1 for details) offer more bandwidth capacity for short distance networks. A consideration for using multimode fibre is the connection to the existing fibre base, which is most likely to single-mode fibre. This will require some form of intermediate active equipment. Multimode fibres can successfully be installed in flats or multitenant buildings using a local active node (in the basement).