Fiber to the x

A schematic illustrating how 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. Dotted rectangles represent separate living or office spaces within the same building.

Fiber to the x (FTTX) is a generic term for any broadband network architecture using optical fiber to provide all or part of the local loop used for last mile telecommunications. As fiber optic cables are able to carry much more data than copper cables, especially over long distances, copper telephone networks built in the 20th Century are being replaced by fiber.

FTTX is a generalization for several configurations of fibre deployment, arranged into two groups: FTTP/FTTH/FTTB (Fiber laid all the way to the premises/home/building) and FTTC/N (fiber laid to the cabinet/node, with copper wires completing the connection).

Definitions

The telecommunications industry differentiates between several distinct FTTX configurations. The terms in most widespread use today are:

• FTTP (fiber-to-the-premises): This term is used either as a blanket term for both FTTH and FTTB, or where the fiber network includes both homes and small businesses.
  • FTTH (fiber-to-the-home): Fiber reaches the boundary of the living space, such as a box on the outside wall of a home. Passive optical networks and point-to-point Ethernet are architectures that deliver triple-play services over FTTH networks directly from an operator's central office.^[1][2]
  • FTTB (fiber-to-the-building, -business, or -basement): Fiber reaches the boundary of the building, such as the basement in a multi-dwelling unit, with the final connection to the individual living space being made via alternative means, similar to the curb or pole technologies.
  • FTTD (fiber-to-the-desktop): Fiber connection is installed from the main computer room to a terminal or fiber media converter near the user's desk.
  • FTTE / FTTZ (fiber-to-the-telecom-enclosure or fiber-to-the-zone) is a form of structured cabling typically used in enterprise local area networks, where fiber is used to link the main computer equipment room to an enclosure close to the desk or workstation. FTTE and FTTZ are not considered part of the FTTX group of technologies, despite the similarity in name.^[3]
• FTTdp (Fibre To The Distribution Point) This is very similar to FTTC / FTTN but is one-step close again moving the end of the fiber to within meters of the boundary of the customers premises in last junction possible junction box known as the "distribution point" this allows for near-gigabit speeds^[4]
• FTTN / FTTLA (fiber-to-the-node, -neighborhood, or -last-amplifier): Fiber is terminated in a street cabinet, possibly miles away from the customer premises, with the final connections being copper. FTTN is often an interim step toward full FTTH (fiber-to-the-home) and is typically used to deliver 'advanced' triple-play telecommunications services.
• FTTC / FTTK (fiber-to-the-curb/kerb, -closet, or -cabinet): This is very similar to FTTN, but the street cabinet or pole is closer to the user's premises, typically within 1,000 feet (300 m), within range for high-bandwidth copper technologies such as wired ethernet or IEEE 1901 power line networking and wireless Wi-Fi technology. FTTC is occasionally ambiguously called FTTP (fiber-to-the-pole), leading to confusion with the distinct fiber-to-the-premises system.

To promote consistency, especially when comparing FTTH penetration rates between countries, the three FTTH Councils of Europe, North America, and Asia-Pacific agreed upon definitions for FTTH and FTTB in 2006,^[5] with an update in 2009,^[6] 2011^[7] and another in 2015.^[8] The FTTH Councils do not have formal definitions for FTTC and FTTN.

Benefits

While fibre optic cables can carry data at high speeds over long distances, copper cables used in traditional telephone lines and ADSL cannot. For example, the common form of gigabit Ethernet (1Gbit/s) runs over relatively economical category 5e, category 6 or augmented category 6 unshielded twisted-pair copper cabling but only to 100 m (330 ft). However, 1 Gbit/s ethernet over fiber can easily reach tens of kilometres. Therefore, FTTP has been selected by every major communications provider in the world to carry data over long 1 Gbit/s symmetrical connections directly to consumer homes. FTTP configurations that bring fiber directly into the building can offer the highest speeds since the remaining segments can use standard ethernet or coaxial cable. Google Fiber provides speed of 1 Gbit/s.^[9]

Fiber is often said to be "future-proof" because the data rate of the connection is usually limited by the terminal equipment rather than the fiber, permitting substantial speed improvements by equipment upgrades before the fiber itself must be upgraded. Still, the type and length of employed fibers chosen, e.g. multimode vs. single-mode, are critical for applicability for future connections of over 1 Gbit/s.

FTTC (where fiber transitions to copper in a street cabinet) is generally too far from the users for standard ethernet configurations over existing copper cabling. They generally use very-high-bit-rate digital subscriber line (VDSL) at downstream rates of 80 Mbit/s, but this falls extremely quickly over a distance of 100 metres.

Fiber to the premises

Fiber to the premises (FTTP) is a form of fiber-optic communication delivery, in which an optical fiber is run in an optical distribution network from the central office all the way to the premises occupied by the subscriber. The term "FTTP" has become ambiguous and may also refer to FTTC where the fiber terminates at a utility pole without reaching the premises.

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

• FTTH (fiber-to-the-home) is a form of fiber-optic communication delivery that reaches one living or working space. The fiber extends from the central office to the subscriber's living or working space.^[7] Once at the subscriber's living or working space, the signal may be conveyed throughout the space using any means, including twisted pair, coaxial cable, wireless, power line communication, or optical fiber.
• FTTB (fiber-to-the-building or -basement) is a form of fiber-optic communication delivery that necessarily applies only to those properties that contain multiple living or working spaces. The optical fiber terminates before actually reaching the subscribers living or working space itself, but does extend to the property containing that living or working space. The signal is conveyed the final distance using any non-optical means, including twisted pair, coaxial cable, wireless, or power line communication.^[7]

An apartment building may provide an example of the distinction between FTTH and FTTB. If a fiber is run to a panel inside each subscriber's apartment unit, it is FTTH. If instead the fiber goes only as far as the apartment building's shared electrical room (either only to the first floor or to each floor), it is FTTB.

Fiber to the curb/cabinet/node

The inside of a fiber cabinet. The left-hand side contains the fiber, and the right-hand side contains the copper.

Fiber to the curb/cabinet (FTTC) 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. The "curb" is an abstraction and can just as easily mean a pole-mounted device or communications closet or shed. Typically any system terminating fiber within 1,000 ft (300 m) of the customer premises equipment would be described as FTTC.

Fiber to the node or neighborhood (FTTN), sometimes identified with and sometimes distinguished from fiber to the cabinet (FTTC),^[10] is a telecommunication architecture based on fiber-optic cables run to a cabinet serving a neighborhood. Customers typically connect to this cabinet using traditional coaxial cable or twisted pair wiring. The area served by the cabinet is usually less than one mile in radius and can contain several hundred customers. (If the cabinet serves an area of less than 1,000 ft (300 m) in radius, the architecture is typically called FTTC/FTTK.)^[11]

FTTN 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 digital subscriber line (DSL) are used between the cabinet and the customers. Data rates vary according to the exact protocol used and according to how close the customer is to the cabinet.

Unlike FTTP, FTTN often uses existing coaxial or twisted-pair infrastructure to provide last mile service and is thus less costly to deploy. In the long term, however, its bandwidth potential is limited relative to implementations that bring the fiber still closer to the subscriber.

A variant of this technique for cable television providers is used in a hybrid fiber-coaxial (HFC) system. It is sometimes given the acronym FTTLA (fiber-to-the-last-amplifier) when it replaces analog amplifiers up to the last one before the customer (or neighborhood of customers).

FTTC allows delivery of broadband services such as high-speed internet. Usually existing wire is used with communications protocols such as broadband cable access (typically DOCSIS) or some form of DSL connecting the curb/cabinet and the customers. In these protocols, the data rates vary according to the exact protocol used and according to how close the customer is to the cabinet.

Where it is feasible to run new cable, both fiber and copper ethernet are capable of connecting the "curb" with a full 100Mbit/s or 1Gbit/s connection. Even using relatively cheap outdoor category 5 copper over thousands of feet, all ethernet protocols including power over ethernet (PoE) are supported. Most fixed wireless technologies rely on PoE, including Motorola Canopy, which has low-power radios capable of running on a 12VDC power supply fed over several hundred feet of cable.

Power line networking deployments also rely on FTTC. Using the IEEE P1901 protocol (or its predecessor HomePlug AV) existing electric service cables move up to 1Gbit/s from the curb/pole/cabinet into every AC electrical outlet in the home—coverage equivalent to a robust Wi-Fi implementation, with the added advantage of a single cable for power and data.

By avoiding new cable and its cost and liabilities, FTTC costs less to deploy. However, it also has historically had lower bandwidth potential than FTTP. In practice, the relative advantage of fiber depends on the bandwidth available for backhaul, usage-based billing restrictions that prevent full use of last-mile capabilities, and customer premises equipment and maintenance restrictions, and the cost of running fiber that can vary widely with geography and building type.

In the United States and Canada, 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.^[12] Verizon, meanwhile, announced in March 2010 they were winding down Verizon FiOS expansion, concentrating on completing their network in areas that already had FiOS franchises but were not deploying to new areas, suggesting that FTTH was uneconomic beyond these areas.

Verizon also announced (at CES 2010) its entry into the smart home and power utility data management arenas, indicating it was considering using P1901-based FTTC or some other existing-wire approach to reach into homes, and access additional revenues from the secure AES-128 bandwidth required for advanced metering infrastructure. However, the largest 1Gbit/s deployment in the United States, in Chattanooga, Tennessee, despite being conducted by power utility EPB,^[13] was FTTH rather than FTTC, reaching every subscriber in a 600-square-mile area. Monthly pricing of $350 reflected this generally high cost of deployment. However, Chattanooga EPB has reduced the monthly pricing to $70/month.^[14]

Historically, both telephone and cable companies avoided hybrid networks using several different transports from their point of presence into customer premises. The increased competitive cost pressure, availability of three different existing wire solutions, smart grid deployment requirements (as in Chattanooga), and better hybrid networking tools (with major vendors like Alcatel-Lucent and Qualcomm Atheros, and Wi-Fi solutions for edge networks, IEEE 1905 and IEEE 802.21 protocol efforts and SNMP improvements) all make FTTC deployments more likely in areas uneconomic to serve with FTTP/FTTH. In effect FTTC serves as a halfway measure between fixed wireless and FTTH, with special advantages for smart appliances and electric vehicles that rely on PLC use already.

Deployments

FTTP

Copper telephone networks built in the 20th Century are being replaced by FTTP in nearly every country in the world. Much of the transition is expected to be complete by 2030.^[15]

FTTN and FTTC

FTTN/C is seen as an interim step towards full FTTH and in many cases triple-play services delivered using this approach have been proven to grow subscriber numbers and ARPU considerably ^[16][17][18] FTTN/C is currently used by a number of operators, including AT&T in the United States, Germany's Deutsche Telekom, Greece's OTE, Swisscom, Belgacom in Belgium, and Canadian operators Telus and Bell Canada.

Optical distribution networks

Direct fiber

The simplest optical distribution network architecture is direct fiber: each fiber leaving the central office goes to exactly one customer. Such networks can provide excellent bandwidth but are more costly due to the fiber and central office machinery.^[19]

Direct fiber is generally favored by new entrants and competitive operators. A benefit is that no layer 2 networking technologies are excluded, whether passive optical network (PON), active optical network (AON), or other. Any form of regulatory remedy is possible using this topology.^[20]

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. AONs and PONs both achieve this split.

Active optical network

Comparison showing how a typical AON (a star network capable of multicasting) handles downstream traffic differently from a typical PON (a star network having multiple splitters housed in the same cabinet).

AONs rely on electrically powered network equipment to distribute the signal, such as a switch or router. Normally, signals need optical-electrical-optical transformation in the AON. Each signal leaving the central office is directed only to the customer for whom it is intended.

Incoming signals from the customers avoid colliding at the intersection because the powered equipment there provides buffering. Active ethernet (a type of ethernet in the first mile) is a common AON, which uses optical ethernet switches to distribute the signal, incorporating the customers' premises and the central office into a large switched ethernet network.

Such networks are identical to 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 location. Each switching cabinet can handle up to 1,000 customers, although 400–500 is more typical.

This neighborhood equipment performs layer 2 switching or 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 100Mbit/s, full-duplex, over one single-mode optical fiber FTTP, depending on the provider. Speeds of 1Gbit/s are becoming commercially available.

Passive optical network

A passive optical network (PON) is a point-to-multipoint FTTP network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve up to 128 customers. A PON reduces the fiber and central office equipment required compared with point-to-point architecture.

Downstream signal coming from the central office is broadcast to each customer premises sharing a fiber. Encryption is used to prevent eavesdropping. Upstream signals are combined using a multiple-access protocol, usually time division multiple access (TDMA).

Ethernet point-to-point

Point-to-point protocol over Ethernet (PPPoE) is a common way of delivering triple- and quad-play (voice, video, data, and mobile) services over both fiber and hybrid fiber-coaxial (HFC) networks. Active PPPoE uses dedicated fiber from an operator's central office all the way to the subscribers' homes, while hybrid networks (often FTTN) use it to transport data via fiber to an intermediate point to ensure sufficiently high throughput speeds over last mile copper connections.

This approach has become increasingly popular in recent years with telecoms service providers in both North America (AT&T, Telus, for example) and Europe's Fastweb, Telecom Italia, Telekom Austria and Deutsche Telekom, for example. Google has also looked into this approach, amongst others, as a way to deliver multiple services over open-access networks in the United States.^[21]

Electrical network

Once on private property, the signal is typically converted into an electrical format.

The optical network terminal (ONT, an ITU-T term) or unit (ONU, an identical IEEE term) converts the optical signal into an electrical signal using thin film filter technology. These units require electrical power for their operation, so some providers connect them to backup batteries in case of power outages to ensure emergency access to telecommunications. The optical line terminations "range" the optical network terminals or units in order to provide TDMA time slot assignments for upstream communication.

For FTTH and for some forms of FTTB, it is common for the building's existing ethernet, phone and cable TV systems to connect directly to the optical network terminal or unit. If all three systems cannot directly reach the unit, it is possible to combine signals and transport them over a common medium such as ethernet. Once closer to the end user, equipment such as a router or network interface controller can separate the signals and convert them into the appropriate protocol.

For FTTC and FTTN, the combined internet, video and telephone signal travels to the building over existing telephone or cable wiring until it reaches the end-user's living space, where a VDSL or DOCSIS modem converts data and video signals into ethernet protocol, which is sent over the end-user's category 5 cable.

See also

• Next generation access
• Hybrid fiber-coaxial
• Fiber in the loop
• Internet access

References

External links

Wikimedia Commons has media related to Fiber to the x.

• Fiber to the Home Council: Asia-Pacific
• Fibre to the Home Council: Europe
• Fiber to the Home Council: North America
• Fiber to the Home Council: Latin America Chapter

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