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48-408: VDSL offers speeds of up to 52  Mbit/s downstream and 16 Mbit/s upstream , over a single twisted pair of copper wires using the frequency band from 25  kHz to 12 MHz. These rates mean that VDSL is capable of supporting applications such as high-definition television , as well as telephone services ( voice over IP ) and general Internet access , over a single connection. VDSL

96-436: A binit as an arbitrary information unit equivalent to some fixed but unspecified number of bits. Hybrid Access Networks Hybrid Access Networks refer to a special architecture for broadband access networks where two different network technologies are combined to improve bandwidth. A frequent motivation for such Hybrid Access Networks to combine one xDSL network with a wireless network such as LTE . The technology

144-409: A byte or word , is referred to, it is usually specified by a number from 0 upwards corresponding to its position within the byte or word. However, 0 can refer to either the most or least significant bit depending on the context. Similar to torque and energy in physics; information-theoretic information and data storage size have the same dimensionality of units of measurement , but there

192-502: A unit of information , the bit is also known as a shannon , named after Claude E. Shannon . The symbol for the binary digit is either "bit", per the IEC 80000-13 :2008 standard, or the lowercase character "b", per the IEEE 1541-2002 standard. Use of the latter may create confusion with the capital "B" which is the international standard symbol for the byte. The encoding of data by discrete bits

240-482: A Bell Labs memo on 9 January 1947 in which he contracted "binary information digit" to simply "bit". A bit can be stored by a digital device or other physical system that exists in either of two possible distinct states . These may be the two stable states of a flip-flop , two positions of an electrical switch , two distinct voltage or current levels allowed by a circuit , two distinct levels of light intensity , two directions of magnetization or polarization ,

288-429: A bit was represented by the polarity of magnetization of a certain area of a ferromagnetic film, or by a change in polarity from one direction to the other. The same principle was later used in the magnetic bubble memory developed in the 1980s, and is still found in various magnetic strip items such as metro tickets and some credit cards . In modern semiconductor memory , such as dynamic random-access memory ,

336-723: A much slower rate from there, and outperforms VDSL. Starting from 1,600 m (1 mi) its performance is equal to ADSL2+ . ADSL -like long-reach performance is one of the key advantages of VDSL2. LR-VDSL2 enabled systems are capable of supporting speeds of around 1–4 Mbit/s (downstream) over distances of 4–5 km (2.5–3 miles), gradually increasing the bit rate up to symmetric 100 Mbit/s as loop-length shortens. This means that VDSL2-based systems, unlike VDSL systems, are not limited to short local loops or MTU/MDUs only, but can also be used for medium range applications. Bonding (ITU-T G.998.x) may be used to combine multiple wire pairs to increase available capacity, or extend

384-404: A time in serial transmission , and by a multiple number of bits in parallel transmission . A bitwise operation optionally processes bits one at a time. Data transfer rates are usually measured in decimal SI multiples of the unit bit per second (bit/s), such as kbit/s. In the earliest non-electronic information processing devices, such as Jacquard's loom or Babbage's Analytical Engine , a bit

432-408: A variable separating frequency between the second downstream band, and the second upstream band. All VDSL1 bandplans have spectrum up to 12 MHz, so the length of the copper loops must be shorter than ADSL. The VDSL2 standard defines a wide range of profiles that can be used in different VDSL deployment architectures; in the central office, in the cabinet or in the building for example. Vectoring

480-437: Is a transmission method that employs the coordination of line signals for reduction of crosstalk levels and improvement of performance. It is based on the concept of noise cancellation , much like noise-cancelling headphones . The ITU-T G.993.5 standard, "Self-FEXT cancellation (vectoring) for use with VDSL2 transceivers" (2010), also known as G.vector , describes vectoring for VDSL2. The scope of Recommendation ITU-T G.993.5

528-505: Is achieved at a range of about 300 metres (980 ft); performance degrades as the local loop attenuation increases. The concept of VDSL was first published in 1991 through a joint Bellcore - Stanford research study. The study searched for potential successors to the then-prevalent HDSL and relatively new ADSL , which were both 1.5 Mbit/s. Specifically, it explored the feasibility of symmetric and asymmetric data rates exceeding 10 Mbit/s on short phone lines. VDSL2 standard

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576-658: Is an enhancement to ITU T G.993.1 that supports asymmetric and symmetric transmission at a bidirectional net data rate up to 400 Mbit/s on twisted pairs using a bandwidth up to 35 MHz. A VDSL connection uses up to seven frequency bands, so one can allocate the data rate between upstream and downstream differently depending on the service offering and spectrum regulations. The first-generation VDSL standard specified both quadrature amplitude modulation (QAM) and discrete multi-tone modulation (DMT). In 2006, ITU-T standardized VDSL in recommendation G.993.2 which specified only DMT modulation for VDSL2. [REDACTED] VDSL2

624-515: Is an enhancement to VDSL designed to support the wide deployment of triple play services such as voice, video, data and high-definition television (HDTV) VDSL2 is intended to enable operators and carriers to gradually, flexibly, and cost-efficiently upgrade existing xDSL infrastructure. The protocol is standardized in the International Telecommunication Union telecommunications sector ( ITU-T ) as Recommendation G.993.2. It

672-559: Is deployed over existing wiring used for analog telephone service and lower-speed DSL connections. This standard was approved by the International Telecommunication Union (ITU) in November 2001. Second-generation systems ( VDSL2 ; ITU-T G.993.2 approved in February 2006) use frequencies of up to 30 MHz to provide data rates exceeding 100 Mbit/s simultaneously in both the upstream and downstream directions. The maximum available bit rate

720-503: Is generic and can be applied to combine different types of access networks such as DOCSIS , WiMAX , 5G or satellite networks. The Broadband Forum has specified an architecture as a framework for the deployment of such converged networks. One of the main motivations for such Hybrid Access Networks is to provide faster Internet services in rural areas where it is not always cost-effective to deploy faster xDSL technologies such as G.Fast or VDSL2 that cannot cover long distances between

768-486: Is in general no meaning to adding, subtracting or otherwise combining the units mathematically, although one may act as a bound on the other. Units of information used in information theory include the shannon (Sh), the natural unit of information (nat) and the hartley (Hart). One shannon is the maximum amount of information needed to specify the state of one bit of storage. These are related by 1 Sh ≈ 0.693 nat ≈ 0.301 Hart. Some authors also define

816-448: Is incompatible with local-loop unbundling , but future standard amendments could bring a solution. Supervectoring  [ de ] is an evolution of the vectoring technology invented and widely implemented by Deutsche Telekom , which further increases crosstalk and interference resistance and allows for stable internet at home connections at 250  Mbit/s downstream and 100 Mbit/s upstream . Mbit The bit

864-554: Is more compressed—the same bucket can hold more. For example, it is estimated that the combined technological capacity of the world to store information provides 1,300 exabytes of hardware digits. However, when this storage space is filled and the corresponding content is optimally compressed, this only represents 295 exabytes of information. When optimally compressed, the resulting carrying capacity approaches Shannon information or information entropy . Certain bitwise computer processor instructions (such as bit set ) operate at

912-497: Is specifically limited to the self-FEXT ( far-end crosstalk ) cancellation in the downstream and upstream directions. The far-end crosstalk (FEXT) generated by a group of near-end transceivers and interfering with the far-end transceivers of that same group is cancelled. This cancellation takes place between VDSL2 transceivers, not necessarily of the same profile. The technology is analogous to G.INP and Seamless Rate Adaptation (SRA). Although technically feasible, as of 2022, vectoring

960-424: Is the most basic unit of information in computing and digital communication . The name is a portmanteau of binary digit . The bit represents a logical state with one of two possible values . These values are most commonly represented as either " 1 " or " 0 " , but other representations such as true / false , yes / no , on / off , or + / − are also widely used. The relation between these values and

1008-413: Is to efficiently use the two access links even if they have different delay and bandwidth. One technical difficulty that occurs when distributing packets over such heterogeneous links is to accurately detect congestion, notably on the wireless network whose bandwidth can vary quickly, and cope with the reordering which is caused by the delay difference. One approach uses GRE tunnels to hide the two links to

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1056-473: Is where the network operator provides a hybrid CPE router to each subscriber and installs a Hybrid Aggregation Gateway (HAG) inside its access networks. The Hybrid Aggregation Gateway plays an important role in balancing the packets sent by and destined to the hybrid CPE router over the two access networks. Two technologies have been defined and deployed to enable hybrid CPE routers to interact with Hybrid Aggregation Gateways. The main objective of these technologies

1104-410: The yottabit (Ybit). When the information capacity of a storage system or a communication channel is presented in bits or bits per second , this often refers to binary digits, which is a computer hardware capacity to store binary data ( 0 or 1 , up or down, current or not, etc.). Information capacity of a storage system is only an upper bound to the quantity of information stored therein. If

1152-449: The 1940s, computer builders experimented with a variety of storage methods, such as pressure pulses traveling down a mercury delay line , charges stored on the inside surface of a cathode-ray tube , or opaque spots printed on glass discs by photolithographic techniques. In the 1950s and 1960s, these methods were largely supplanted by magnetic storage devices such as magnetic-core memory , magnetic tapes , drums , and disks , where

1200-409: The ambiguity of relying on the underlying hardware design, the unit octet was defined to explicitly denote a sequence of eight bits. Computers usually manipulate bits in groups of a fixed size, conventionally named " words ". Like the byte, the number of bits in a word also varies with the hardware design, and is typically between 8 and 80 bits, or even more in some specialized computers. In

1248-424: The average. This principle is the basis of data compression technology. Using an analogy, the hardware binary digits refer to the amount of storage space available (like the number of buckets available to store things), and the information content the filling, which comes in different levels of granularity (fine or coarse, that is, compressed or uncompressed information). When the granularity is finer—when information

1296-652: The copper network's reach. Hybrid Access Networks can be used to combine xDSL with wireless networks. This enables network operators to provide faster Internet access services over long lines. Vplus is a technology to achieve higher speeds over existing VDSL2 networks. It was developed by Alcatel-Lucent and standardised in November 2015 in ITU G.993.2 Amendment 1 as VDSL2 profile 35b. It promises to deliver speeds of up to 300 Mbit/s downstream and 100 Mbit/s upstream on loops shorter than 250 m. On longer loops, Vplus falls back to VDSL2 17a vectoring performance. Vplus uses

1344-415: The early 21st century, retail personal or server computers have a word size of 32 or 64 bits. The International System of Units defines a series of decimal prefixes for multiples of standardized units which are commonly also used with the bit and the byte. The prefixes kilo (10 ) through yotta (10 ) increment by multiples of one thousand, and the corresponding units are the kilobit (kbit) through

1392-420: The end user might have two different access routers that are linked together by a cable instead of a single hybrid CPE router. The first deployment scenario is where the network operator provides a hybrid CPE router to each subscriber but no specialised equipment in the operator's network. There are two possible configurations for IP addresses. A first deployment scenario is to allocate different IP addresses to

1440-496: The hybrid network access and use the wireless leg while the network operator is installing the wired part. Several techniques are defined by the Broadband Forum to create Hybrid Access Networks. To illustrate them, we assume that the end user has an hybrid CPE ( Customer-premises_equipment ) router that is attached to both a wired access network such as xDSL and a wireless one such as LTE . Other deployments are possible, e.g.,

1488-409: The level of manipulating bits rather than manipulating data interpreted as an aggregate of bits. In the 1980s, when bitmapped computer displays became popular, some computers provided specialized bit block transfer instructions to set or copy the bits that corresponded to a given rectangular area on the screen. In most computers and programming languages, when a bit within a group of bits, such as

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1536-408: The orientation of reversible double stranded DNA , etc. Bits can be implemented in several forms. In most modern computing devices, a bit is usually represented by an electrical voltage or current pulse, or by the electrical state of a flip-flop circuit. For devices using positive logic , a digit value of 1 (or a logical value of true) is represented by a more positive voltage relative to

1584-443: The physical states of the underlying storage or device is a matter of convention, and different assignments may be used even within the same device or program . It may be physically implemented with a two-state device. A contiguous group of binary digits is commonly called a bit string , a bit vector, or a single-dimensional (or multi-dimensional) bit array . A group of eight bits is called one  byte , but historically

1632-517: The representation of 0 . Different logic families require different voltages, and variations are allowed to account for component aging and noise immunity. For example, in transistor–transistor logic (TTL) and compatible circuits, digit values 0 and 1 at the output of a device are represented by no higher than 0.4 V and no lower than 2.6 V, respectively; while TTL inputs are specified to recognize 0.8 V or below as 0 and 2.2 V or above as 1 . Bits are transmitted one at

1680-466: The same tone spacing as VDSL2 17a to allow vectoring across Vplus (35b) and 17a lines, and thus mixed deployments and a smooth introduction of Vplus. The VDSL1 standard has three bandplans: Annex A (Asymmetric BandPlan), Annex B (Symmetric BandPlan) and Annex C (Fx BandPlan). Annex A and Annex B were formerly called Plan 998 and Plan 997 respectively. VDSL1 Annex C is intended for use in Sweden only and it uses

1728-424: The size of the byte is not strictly defined. Frequently, half, full, double and quadruple words consist of a number of bytes which is a low power of two. A string of four bits is usually a nibble . In information theory , one bit is the information entropy of a random binary variable that is 0 or 1 with equal probability, or the information that is gained when the value of such a variable becomes known. As

1776-498: The street cabinet and the home. Several governments, notably in Europe, required network operators to provide fast Internet services to all inhabitants with a minimum of 30 Mbps by 2020. A second use case is to improve the reliability of the access link given that it is unlikely that both the xDSL network and the wireless network will fail at the same time. A third motivation is the fast service turnup. The customer can immediately install

1824-552: The thickness of alternating black and white lines. The bit is not defined in the International System of Units (SI). However, the International Electrotechnical Commission issued standard IEC 60027 , which specifies that the symbol for binary digit should be 'bit', and this should be used in all multiples, such as 'kbit', for kilobit. However, the lower-case letter 'b' is widely used as well and

1872-556: The two possible values of one bit of storage are not equally likely, that bit of storage contains less than one bit of information. If the value is completely predictable, then the reading of that value provides no information at all (zero entropic bits, because no resolution of uncertainty occurs and therefore no information is available). If a computer file that uses n  bits of storage contains only m  <  n  bits of information, then that information can in principle be encoded in about m  bits, at least on

1920-444: The two values of a bit may be represented by two levels of electric charge stored in a capacitor . In certain types of programmable logic arrays and read-only memory , a bit may be represented by the presence or absence of a conducting path at a certain point of a circuit. In optical discs , a bit is encoded as the presence or absence of a microscopic pit on a reflective surface. In one-dimensional bar codes , bits are encoded as

1968-483: The upper layer protocol. Both the hybrid CPE and the HAG need to reorder the received packets to ensure that TCP receives in-sequence packets. The second approach uses Multipath TCP , a recent TCP extension that has been designed to enable the transmission of the packets that belong to a single session across different links. This approach leverages the ability of MPTCP to efficiently handle congestion and cope with reordering on

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2016-490: The wired and wireless interfaces. In this case, the hybrid CPE router needs to load-balance intelligently the packets over the two networks. In particular, it must ensure that all packets belonging to a given TCP connection are sent over the same interface. A second deployment scenario is to allocate the same IP address to both the wired and the wireless networks and configure the routing in these networks to ensure that packets are correctly routed. The second deployment scenario

2064-447: Was also used in Morse code (1844) and early digital communications machines such as teletypes and stock ticker machines (1870). Ralph Hartley suggested the use of a logarithmic measure of information in 1928. Claude E. Shannon first used the word "bit" in his seminal 1948 paper " A Mathematical Theory of Communication ". He attributed its origin to John W. Tukey , who had written

2112-561: Was announced as finalized on 27 May 2005, and first published on 17 February 2006. Several corrections and amendments were published from 2007 to 2011. VDSL2 permits the transmission of asymmetric and symmetric aggregate data rates up to 300+ Mbit/s downstream and upstream on twisted pairs using a bandwidth up to 35 MHz on its latest version. It deteriorates quickly from a theoretical maximum of 350 Mbit/s at source to 100 Mbit/s at 500 m (1640.42 ft) and 50 Mbit/s at 1000 m (3280.84 ft), but degrades at

2160-460: Was often stored as the position of a mechanical lever or gear, or the presence or absence of a hole at a specific point of a paper card or tape . The first electrical devices for discrete logic (such as elevator and traffic light control circuits , telephone switches , and Konrad Zuse's computer) represented bits as the states of electrical relays which could be either "open" or "closed". When relays were replaced by vacuum tubes , starting in

2208-503: Was recommended by the IEEE 1541 Standard (2002) . In contrast, the upper case letter 'B' is the standard and customary symbol for byte. Multiple bits may be expressed and represented in several ways. For convenience of representing commonly reoccurring groups of bits in information technology, several units of information have traditionally been used. The most common is the unit byte , coined by Werner Buchholz in June 1956, which historically

2256-541: Was used in the punched cards invented by Basile Bouchon and Jean-Baptiste Falcon (1732), developed by Joseph Marie Jacquard (1804), and later adopted by Semyon Korsakov , Charles Babbage , Herman Hollerith , and early computer manufacturers like IBM . A variant of that idea was the perforated paper tape . In all those systems, the medium (card or tape) conceptually carried an array of hole positions; each position could be either punched through or not, thus carrying one bit of information. The encoding of text by bits

2304-405: Was used to represent the group of bits used to encode a single character of text (until UTF-8 multibyte encoding took over) in a computer and for this reason it was used as the basic addressable element in many computer architectures . The trend in hardware design converged on the most common implementation of using eight bits per byte, as it is widely used today. However, because of

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