The most expensive element in delivering broadband Internet services over fiber optic cable is the access network, and its architecture largely determines how much bandwidth can be delivered to a subscriber. In brownfield installations (with copper local loop already installed), the most expensive element is the labor to install fiber.

There are three elements to a typical broadband fiber access network: the feeder portion, the distribution portion, and the drop cables to the subscribers’ premises. Where fiber is deployed in place of copper determines the fundamental architecture of the access network. For telcos, the three major architectures are Fiber to the Node (FTTN), Fiber to the Curb (FTTC), and Fiber to the Premises (FTTP), and each has a different proportion of fiber. FTTN and FTTC are hybrids combining fiber with copper local loops and are attractive owing to their cost-efficiency in brownfield installations. FTTP is entirely fiber from the wire center to the subscriber.

FTTN

If only the feeder portion of the access network has fiber optic cables, and copper local loops are served with DSL (Digital Subscriber Line) from the Feeder Distribution Hub, then the architecture is known as Fiber to the Node or FTTN (BT confusingly refers to this architecture as Fiber to the Cabinet or FTTC). The feeder portion of the access network is from the wire center (or Central Office) to a Feeder Distribution Hub. A typical network architecture for FTTN is shown below.

The picture below is of a FTTN installation about one mile from my house. TThe rear beige cabinet is a Digital Loop Carrier (DLC) system, which houses telephony electronics. The two beige cabinets in front of the DLC house adjunct DSLAMs providing DSL services. The green cabinet to the right is the Feeder Distribution Interface, which provides copper pair concentration (typically 2 distribution pairs for each feeder pair, which in this case are only a few feet in length).

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FTTC

If fiber is installed in the feeder and distribution portions of the access network, and DSL copper from there to businesses and homes, then this architecture is known as Fiber to the Curb or FTTC. The distribution portion of the broadband access network distributes fiber from the Fiber Distribution Hub to the drop portion of the network, which usually begins at the curb. The diagram below represents a typical FTTC network architecture.

FTTP

If fiber is installed in the feeder, distribution, and drop portions of the broadband access network, then the architecture is known as Fiber to the Premises or FTTP. FTTP is known as Fiber to the Home (FTTH) when serving residential subscribers and as Fiber to the Building (FTTB) when serving buildings such as multi-tenant office buildings. With FTTB, fiber enters the building, but subscribers are served directly with DSL or Ethernet. FTTB is especially common in Japan and Korea, which lead in broadband rates.

Common FTTP technologies include the various PON alternatives (Broadband PON or BPON, Gigabit PON or GPON, Ethernet PON or EPON, and Wave Division Multiplex PON or WDM PON), Active Ethernet, and Active Fiber. With PON, an optical splitter (Arrayed WaveGuide with WDM PON) is installed at the Feeder Distribution Hub with possibly another splitter at the curb. With Active Ethernet, an OutSide Plant (OSP) Ethernet switch is installed at the Fiber Distribution Hub. With an Active Fiber network, only fiber cables and cross-connects are installed in the access network between the wire center and subscribers’ premises.

In brownfield applications, FTTP is the most expensive alternative for a broadband access network. The most costly element per subscriber is the fiber drop cable serving that subscriber’s premises, and the attraction of FTTC is that it avoids this cost. In greenfield installations, FTTP is not significantly more expensive (if at all) compared to copper or coax.  A representative FTTP architecture is shown in the diagram below.

Hybrid Versus FTTP

All three fiber access architectures can deliver broadband rates to subscribers. The two hybrid alternatives are generally less expensive, especially in brownfield installations, but also less capable. With fiber rates measured in Gbps, and DSL in Mbps, more fiber equates to greater potential broadband rates. FTTP, of course, provides the ultimate in broadband access.

© 2009, The Product Group LLC. All rights reserved.

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1. Linsey says:

   October 28, 2009 at 3:54 am

   The whole UK is now hooking up with fiber optic lines and we are some of the first in our neighborhood to connect to a 50mbps connection and it really blows you away!