Fiber to the x

A schematic illustrating how the FTTX architectures vary with regard to the distance between the optical fiber and the end-user. The building on the left is the central office; the building on the right is one of the buildings served by the central office. The dotted rectangles represent separate living or office spaces within the same building.

Fiber to the x (FTTX) is a generic term for any network architecture that uses optical fiber to replace all or part of the usual copper local loop used for telecommunications. The four technologies, in order of an increasingly longer fiber loop are:

• Fiber to the node / neighborhood (FTTN) / Fiber to the cabinet (FTTCab)
• Fiber to the curb (FTTC) / Fibre to the kerb (FTTK)
• Fiber to the building (FTTB)
• Fiber to the home (FTTH)

In the actual deployments, the difference between FTTN and FTTC is quite subtle and is mostly that the latter is nearer the customer than the former.

The broadly-defined term fiber to the premises (FTTP) is sometimes used to describe FTTH and/or FTTB.

Fibers

Fiber to the node

Fiber to the node (FTTN), also called fiber to the neighborhood or fiber to the cabinet (FTTCab), is a telecommunication architecture based on fiber-optic cables run to a cabinet serving a neighborhood. Customers connect to this cabinet using traditional coaxial cable or twisted pair wiring. The area served by the cabinet is usually less than 1,500 m in radius and can contain several hundred customers. (If the cabinet serves an area of less than 300 m in radius then the architecture is typically called fiber to the curb.)

Fiber to the node allows delivery of broadband services such as high speed internet. High speed communications protocols such as broadband cable access (typically DOCSIS) or some form of DSL are used between the cabinet and the customers. The data rates vary according to the exact protocol used and according to how close the customer is to the cabinet.

Unlike the competing fiber to the premises (FTTP) technology, fiber to the node can use the existing coaxial or twisted pair infrastructure to provide last mile service. For this reason, fiber to the node costs less to deploy. However, it also has lower bandwidth potential than fiber to the premises.

Fiber to the Telecommunications Enclosure

Diagram originally published by the Fiber Optics LAN Section of the Telecommunications Industry Association

Fiber-to-the-Telecommunications-Enclosure (FTTE) is a standards-compliant structured cabling system architecture that extends the optical fiber backbone network from the equipment room, through the telecom room, and directly to a telecommunications enclosure (TE) installed in a common space to serve a number of users in a work area. Its implementation is based on the TIA/EIA-569-B “Pathways and Spaces” standard, which defines the Telecommunications Enclosure (TE), and TIA/EIA-568-B.1 Addendum 5, which defines the cabling when a TE is used. The FTTE architecture allows for many media choices from the TE to the work area; it may be balanced twisted pair copper, multimode optical fiber, or even wireless if an access point is installed in or near the TE.

Depending on the user’s needs, FTTE can be deployed in low-density or high-density configurations. A low-density system might use one or two inexpensive 8-port Ethernet mini-switches as an example (these switches have eight 10/100 Mbit/s Ethernet copper ports and one 1 Gbit/s Ethernet fiber uplink). A high-density FTTE design might use commonly available 24- or 48-port switches (these switches are configured with one 1 Gbit/s uplink port per twelve 100BASE-TX user ports). This relatively high work area-to-backbone port ratio provides better performance than is typically provided to enterprise users. Both low and high-density FTTE architectures provide excellent performance in terms of bandwidth delivered to the work area.

• Advantages
  • Low Cost
  • Non-blocking or low-blocking performance better supports convergence
  • Extremely flexible to deploy; supports Moves, Adds & Changes
  • Enables consolidation of electronics into a centralized Telecommunications Room
  • Allows the use of a variety of media from the TE to the user
• Disadvantages
  • TE location is near the user and must be secured

Fiber to the curb

Fiber to the curb (FTTC), also called fibre to the kerb (FTTK), is a telecommunications system based on fiber-optic cables run to a platform that serves several customers. Each of these customers has a connection to this platform via coaxial cable or twisted pair.

Fiber to the curb allows delivery of broadband services such as high speed internet. High speed communications protocols such as broadband cable access (typically DOCSIS) or some form of DSL are used between the cabinet and the customers. The data rates vary according to the exact protocol used and according to how close the customer is to the cabinet.

FTTC is subtly distinct from FTTN or FTTP (all are versions of Fiber in the Loop). The chief difference is the placement of the cabinet. FTTC will be placed near the "curb" which differs from FTTN which is placed far from the customer and FTTP which is placed right at the serving location.

Unlike the competing fiber to the premises (FTTP) technology, fiber to the curb can use the existing coaxial or twisted pair infrastructure to provide last mile service. For this reason, fiber to the curb costs less to deploy. However, it also has lower bandwidth potential than fiber to the premises.

In the United States of America, the largest deployment of FTTC was carried out by BellSouth Telecommunications. With the acquisition of BellSouth by AT&T, deployment of FTTC will end. Future deployments will be based on either FTTN or FTTP. Existing FTTC plant may be removed and replaced with FTTP.

Fiber In The Loop

Fiber In The Loop (FITL) is a system implementing or upgrading portions of the POTS local loop with fiber optic technology from the central office of a telephone carrier to a remote Serving Area Interface (SAI) located in a neighborhood or to an Optical Network Unit (ONU) located at the customer premises (residential and/or business). Generally, fiber is used in either all or part of the local loop distribution network. FITL includes various architectures, such as fiber to the curb (FTTC), fiber to the home (FTTH) and fiber to the premises (FTTP).

Residential areas already served by balanced pair distribution plant call for a trade-off between cost and capacity. The closer the fiber head, the higher the cost of construction and the higher the channel capacity. In places not served by metallic facilities, little cost is saved by not running fiber to the home.

A similar network called a hybrid fibre-coaxial (HFC) network is used by cable television operators but is usually not synonymous with "fiber In the loop", although similar advanced services are provided by the HFC network.

Technologies

The two main technologies used for these architectures are VDSL2 (used in FTTN, FTTC and in some FTTB deployments) and PON (the one used in FTTH and in some FTTB deployments)

Fiber to the premises

Fiber to the premises (FTTP) is a form of fiber-optic communication delivery in which an optical fiber is run directly onto the customers' premises. This contrasts with other fiber-optic communication delivery strategies such as fiber to the node (FTTN), fiber to the curb (FTTC), or hybrid fibre-coaxial (HFC), all of which depend upon more traditional methods such as copper wires or coaxial cable for "last mile" delivery.

Fiber to the premises can be further categorized according to where the optical fiber ends:

• FTTH (fiber to the home) is a form of fiber optic communication delivery in which the optical signal reaches the end user's living or office space.

• An optical signal is distributed from the central office over an optical distribution network (ODN). At the endpoints of this network, devices called optical network terminals (ONTs) convert the optical signal into an electrical signal. (For FTTP architectures, these ONTs are located on private property.) The signal usually travels electrically between the ONT and the end-users' devices.

Optical portion

Optical distribution networks have several competing technologies.

Direct fiber

The simplest optical distribution network can be called direct fiber. In this architecture, each fiber leaving the central office goes to exactly one customer. Such networks can provide excellent bandwidth since each customer gets their own dedicated fiber extending all the way to the central office. However, this approach is extremely costly due to the amount of fiber and central office machinery required. It is usually used only in instances where the service area is very small and close to the central office.

Shared fiber

More commonly each fiber leaving the central office is actually shared by many customers. It is not until such a fiber gets relatively close to the customers that it is split into individual customer-specific fibers. There are two competing optical distribution network architectures which achieve this split: active optical networks (AONs) and passive optical networks (PONs)..

Active optical network

Comparison showing how a typical active optical network handles downstream traffic differently than a typical passive optical network. The type of active optical network shown is a star network capable of multicasting. The type of passive optical network shown is a star network having multiple splitters housed in the same cabinet.

Active optical networks rely on some sort of electrically powered equipment to distribute the signal, such as a switch, router, or multiplexer. Each signal leaving the central office is directed only to the customer for which it is intended. Incoming signals from the customers avoid colliding at the intersection because the powered equipment there provides buffering.

As of 2007, the most common type of active optical networks are called active ethernet, a type of ethernet in the first mile (EFM). Active ethernet uses optical ethernet switches to distribute the signal, thus incorporating the customers' premises and the central office into one giant switched ethernet network. Such networks are identical to the ethernet computer networks used in businesses and academic institutions, except that their purpose is to connect homes and buildings to a central office rather than to connect computers and printers within a campus. Each switching cabinet can handle up to 1,000 customers, although 400-500 is more typical. This neighborhood equipment performs layer 2/layer 3 switching and routing, offloading full layer 3 routing to the carrier's central office. The IEEE 802.3ah standard enables service providers to deliver up to 100 Mbit/s full-duplex over one single-mode optical fiber to the premises depending on the provider.

Electrical portion

Once on private property, the signal typically travels the final distance to the end user's equipment using an electrical format.

A device called an optical network terminal (ONT), also called an optical network unit (ONU), converts the optical signal into an electrical signal. (ONT is an ITU-T term, whereas ONU is an IEEE term, but the two terms mean exactly the same thing.) Optical network terminals require electrical power for their operation, so some providers connect them to back-up batteries in case of power outages. Optical network units use thin film filter technology (or more recently dispersion bridge planar lightwave circuit technology) to convert between optical and electrical signals.

For fiber to the home and for some forms of fiber to the building, it is common for the building's existing phone systems, local area networks, and cable TV systems to connect directly to the ONT.

If all three systems cannot directly reach the ONT, it is possible to combine signals and transport them over a common medium. Once closer to the end-user, equipment such as a router, modem, and/or network interface module can separate the signals and convert them into the appropriate protocol. For example, one solution for apartment buildings uses VDSL to combine data (and / or video) with voice. With this approach, the combined signal travels through the building over the existing telephone wiring until it reaches the end-user's living space. Once there, a VDSL modem copies the data and video signals and converts them into ethernet protocol. These are then sent over the end user's category 5 cable. A network interface module can then separate out the video signal and convert it into an RF signal that is sent over the end-user's coaxial cable. The voice signal continues to travel over the phone wiring and is sent through DSL filters to remove the video and data signals. An alternative strategy allows data and / or voice to be transmitted over coaxial cable. In yet another strategy, some office buildings dispense with the telephone wiring altogether, instead using voice over IP phones that can plug directly into the local area network.

Deployment history

Main article: Fiber to the premises by country

See also

• Fiber to the premises
• Hybrid fibre-coaxial
• Fiber-optic communication
• BICSI

External links

• Fiber Optics LAN Section of the Telecommunications Industry Association
• Fiber Optics Association
• Fiber to the Home Council
• Fiber to the Home Council Europe
• The Fiber Optics Weekly Update
• KMI Research Homepage
• FTTH Blog Daily updates on the business and technology of FTTH
• Telephony Magazine - FTTH One-Stop news, metrics, technology, regulatory information and industry commentary
• Kingfisher International Application Notes Fiber Optic Testing information about FTTH backbone Terminology.
• ADC Hosts First Fiber-to-the-Premises Leadership Symposium; Nationwide Series Brings Together Industry Leaders for Education, Discussion of FTTP Deployment.
• Can You Say FTTN? Annie Lindstrom, Telephony Online, Jan 22, 2001
• SBC clarifies FTTN, FTTP plans Ed Gubbins, Telephony Online, Nov 12, 2004
• Easy as 1,2,3,...4 Don McCullough,"OSP Magazine", October 2005

Fiber to the premises

• Fiber to the Home Council: Asia & The Pacific
• Fiber to the Home Council: Europe
• Fiber to the Home Council: Northern America
• KMI Research FTTP article
• FTTH Blog Daily updates on the business and technology of FTTH
• Fiberevolution Frequently updated blog about FTTH and how it will affect business and society
• Kingfisher International Application Notes Fiber Optic Testing information about FTTH backbone Terminology.
• Richardson, TX FTTP Conversion Notes Details of conversion to FTTP in Dallas, TX (USA) suburb of Richardson.
• San Francisco Draft Fiber Study
• UOC University article