FTTX Part 2

FTTN

So one might ask why service providers are not deploying PON everywhere they have a footprint. The answer is that, although PON architectures are a great way to deploy future proof service and lower operational costs, it is very expensive to install. This is primarily due to the initial installation of the fiber to each home. Whether the task is obtaining the right of ways for new cable runs or installing fiber right along side the old copper lines, it is very expensive for a carrier to undertake. Consequently some service providers have taken a hybrid approach known as Fiber to the Node or FTTN. FTTN deploys fiber from the central office just as any FTTH model might, however, instead of terminating the fiber all the way to the subscriber home, it terminates in the existing DSLAM or CATV service cabinet or adjacent to it in a new fiber hub. From there the fiber is converted to DSL and the "last mile" to the subscriber is the traditional copper pair of phone wire. Alternatively, the "last mile" to the subscriber may utilize coaxial cable and connect using the DOCSIS protocol for all services. This model obviously leaves much to be desired in terms of reducing operational expense and complexity. While the complexity of copper lines for DSL or cable equipment may be lessened with the shorter runs of copper, the overall troubleshooting and maintenance of the lines is still a long term requirement. There is also the ongoing operational expense of the electrical power for the equipment as well as periodic replacement of UPS batteries. FTTN makes sense for areas which are served by a relatively new installation of copper cable or where an investment in DSL or cable head end equipment is fairly recent. The decision to deploy FTTN may also be a simple financial business decision to avoid spending too much capital on infrastructure upgrades while preparing for an eventual deployment of fiber all the way to the subscriber premises.

FTTC

Yet another architecture called Fiber to the Curb (FTTC) provides the same approach as FTTN except that the copper cables are much shorter in length because the conversion from fiber to copper occurs very near to the customer premises. A FTTC system will typically situate the service provider's equipment less than 1000 feet from the business or directly at the street outside (i.e., the curb).This results in better network performance in terms of the bandwidth and offers more flexibility of the architecture but still presents the same, albeit decreased, operational concerns as the FTTN architecture.

FTTB

Our final example of a FTTX architecture is the Fiber to the Business model or FTTB. FTTB (sometimes referred to as FTTP or Fiber to the Premises) is not much different from the FTTH model. In fact the only significant difference is that instead of deploying an ONT inside of every business, service providers often install only one to two ONTs within a main point of presense or POP as it is sometimes called. The POP is typically a small room which houses the incoming telephone lines and fiber optic cable equipment for one or more businesses in a building. After deploying a single ONT the service provider can then connect the business to only one of the Ethernet interfaces on the ONT. The RF video port on a FTTB ONT will supply a more powerful RF signal to allow multiple businesses to tap into the connection. This arrangement allows the service provider to offer voice, video, and data service to other businesses which may be in the same building without needing to deploy further equipment or install additional fiber. Often the ONT used is a 4, 8, 12, or even a 24 port model which might even include the ability to derive T1 signals for voice or data service if the customer requires it. FTTB ONTs are typically more robust than their FTTH counterparts. FTTB ONTs may include larger battery backup systems, multiple POTs ports, and their internal Ethernet hardware can accommodate larger quantities of MAC addresses which are used to switch Ethernet traffic between network devices. At the OLT, the service provider may even provide Transparent LAN Service (TLS) to allow a business to connect to another remote office while reducing the customer's networking complexity. TLS allows the businesses' network to switch Ethernet traffic between locations without duplicating network gear such as routers, firewalls, and other WAN connectivity devices at each location. It is important to note that this architecture is often deployed in multiple dwelling unit (MDU) installations as well. This is an identical approach except that the services are provided to apartment or townhome residents rather than individual businesses.