Fiber to the x (FTTx) is a generic term for any broadband network architecture using optical fiber to replace all or part of the usual metal local loop used for last mile telecommunications. The generic term was initially a generalization for several configurations of fiber deployment (FTTN, FTTC, FTTB, FTTH...), all starting by FTT but differentiated by the last letter, which is substituted by an x in the generalization.
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The telecommunications industry differentiates between several distinct configurations. The terms in most widespread use today are:
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,[1] with an update in 2009.[2] The FTTH Councils do not have formal definitions for FTTC and FTTN.
To some, fiber to the telecom enclosure (FTTE) is not considered to be part of the FTTx group of technologies, despite the similarity in name. FTTE is a form of structured cabling typically used in the enterprise local area network, where fiber is used to link the main computer equipment room to an enclosure close to the desk or workstation.[3] 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.[4][5]
BT is deploying a FTTC system in the UK, as part of its NextGen Access scheme (NGA). Speeds of up to 40meg down/10meg up are possible, but can be doubled, according to profile 17a (UK only)
The speeds of fiber optic and copper cables are both limited by length, but copper is much more sharply limited in this respect. For example, the common form of Gigabit Ethernet runs over relatively economical category 5e, category 6, or augmented category 6 unshielded twisted pair copper cabling but only to 100 meters. However, over the right kind of fiber, Gigabit Ethernet can easily reach tens of kilometers.
Even in the commercial world, most computers have copper communication cables. But these cables are short, typically tens of meters. Most metropolitan network links (e.g., those based on telephone or cable television services) are several kilometers long, in the range where fiber significantly outperforms copper. Replacing at least part of these links with fiber shortens the remaining copper segments and allows them to run much faster.
Fiber configurations that bring fiber right into the building can offer the highest speeds since the remaining segments can use standard Ethernet or coaxial cable. Fiber configurations that transition to copper in a street cabinet are generally too far from the users for standard Ethernet configurations over existing copper cabling. They generally use very high bitrate digital subscriber line (VDSL) at downstream rates of several tens of megabits per second.
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 at least some 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 high gigabit connections.
Point-to-Point Protocol over Ethernet is a common way of delivering triple (and quad) play (voice, video, data and mobile) services over both fiber and hybrid fiber coax [HFC] networks. Active Ethernet Point-to-Point uses dedicated fiber from an operator’s central office all the way to the subscribers’ home, while hybrid networks (often FTTN) use it to transport data via fiber to a node, and then to ensure the highest possible 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 Telecom, for example]. Search specialist Google has also looked into this approach, amongst others, as a way to deliver multiple services over open-access networks in the United States.[6]
Fiber to the node (FTTN), also called fiber to the neighborhood or fiber to the cabinet (FTTCab),[7] 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 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.)[8]
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 digital subscriber line (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 technology, fiber to the node often uses the existing coaxial or twisted pair infrastructure to provide last mile service. For this reason, fiber to the node is less costly to deploy. In the long-term, however, its bandwidth potential is limited relative to implementations which 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 FTTN for Fiber To The Last Amplifier when it replaces analog amplifiers up to the last one before the customer (or neighborhood of customers).
Fiber to the curb (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.
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 main 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 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.[9]
Fiber to the premises is a form of fiber-optic communication delivery in which an optical fiber is run in a distribution network from the central office all the way to the premises occupied by the subscriber. Fiber to the premises is often abbreviated with the acronym FTTP. However, this acronym has become ambiguous and may instead refer to a form of fiber to the curb 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:
An apartment building may provide an example of the distinction between FTTH and FTTB. If a fiber is run to a panel at each subscriber's apartment, this is FTTH. If instead the fiber goes only as far as the apartment building's shared electrical room, then this is FTTB.
The deployment of an FTTH network meant Fastweb was the first telecom operator to deliver true triple-play services to its subscribers. This contributed to its ARPU [Average Revenue Per User] being amongst the highest in the industry for a number of years during the early 2000s. Its FTTH network also puts it at the forefront of advanced connected home services.
Both Fiber for Italy participants and Telecom Italia are working with Advanced Digital Broadcast to provide residential gateway technology with embedded fiber termination.
Since 2006, Television Sierre SA deploys a FTTH network in most municipalities in the district of Sierre in Switzerland. Triple Play services are offered to the public under the brand Vario.
In October 2011, British operator Hyperoptic launched a 1Gbit/sec FTTH service in London.[14]
FTTN, or Fiber-to-the-node, is currently used by a number of multiple-service operators to deliver advanced triple play services to consumers, including AT&T in the United States for its U-Verse service, Deutsche Telekom in Germany, Swisscom and Canadian operator Telus. It is seen as an interim step towards full FTTH and in many cases services triple play services delivered using this approach has been proven to grow subscriber numbers and ARPU considerably.[15][16]
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 about 10% more costly due to the amount of fiber and central office machinery required.[17] The approach is generally favored by new entrants and competitive operators. A benefit of this approach is that it doesn't exclude any layer 2 networking technologies, be they Passive optical network, Active Optical Network, etc. From a regulatory point of view it leads to least implications as any form of regulatory remedy is still possible using this topology.[18]
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 networks rely on some sort of electrically powered equipment in Optical Distribution Network(ODN) to distribute the signal, such as a switch or router. Normally, optical signals need O-E-O transformation in ODN. 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. Speeds of 1Gbit/s are becoming commercially available.
A passive optical network (PON) is a point-to-multipoint, fiber to the premises network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 32-128. A PON configuration reduces the amount of fiber and central office equipment required compared with point to point architectures.
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). The OLTs "range" the ONUs in order to provide time slot assignments for upstream communication.
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 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 Internet Protocol phones that can plug directly into the local area network.
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