In telecommunications Telecommunication is the transmission of messages, over significant distances, for the purpose of communication. In earlier times, telecommunications involved the use of visual signals, such as smoke, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded drumbeats, lung-blown horns, or sent by loud whistles, for and computing Computing, also known as computer science, is usually defined as the activity of using and improving computer technology, computer hardware and software. It is the computer-specific part of information technology. Computer science is the study and the science of the theoretical foundations of information and computation and their implementation, bitrate (sometimes written bit rate, data rate or as a variable R or fb) is the number of bits A bit or binary digit is the basic unit of information in computing and telecommunications; it is the amount of information that can be stored by a digital device or other physical system that can usually exist in only two distinct states. These may be the two stable positions of an electrical switch, two distinct voltage or current levels allowed that are conveyed or processed per unit of time.
The bit rate is quantified using the bits per second In telecommunications, bit rate or data transfer rate is the average number of bits, characters, or blocks per unit time passing between equipment in a data transmission system. This is typically measured in multiples of the units bit per second or byte per second (bit/s or bps) unit, often in conjunction with an SI prefix The International System of Units specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decimal multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol. The SI prefixes are standardized by the International such as kilo- The kilo prefix is derived from the Greek word χίλιοι , meaning thousand. It was originally adopted by Antoine Lavoisier and his group in 1795, and introduced into the metric system in France with its establishment in 1799. The General Conference on Weights and Measures was formed in 1875 (kbit/s or kbps), mega- Mega- is an prefix in the metric system denoting a factor of million. Confirmed in 1960, it comes from the Greek μέγας, meaning great (Mbit/s or Mbps), giga- The Oxford English Dictionary reports the earliest written use of giga in this sense to be in the Reports of the IUPAC 14th Conference in 1947: "The following prefixes to abbreviations for the names of units should be used: G giga 109×" (Gbit/s or Gbps) or tera- Confirmed in 1960, it comes from the Greek τέρας, meaning monster. It also bears a resemblance to the Greek prefix τετρα meaning four; the coincidence of it signifying the fourth power of 1000 served as a model for the higher-order prefixes peta, exa, zetta and yotta, all of which are deliberately distorted forms of the Latin or Greek (Tbit/s or Tbps). Note that, unlike many other computer-related units, 1 kbit/s is traditionally defined as 1,000 bit/s, not 1,024 bit/s, etc, also before 1999 when SI prefixes were introduced for units of information in the standard IEC 60027-2 IEC 60027 is the International Electrotechnical Commission's standard on Letter symbols to be used in electrical technology. It consists of several parts:.
The formal abbreviation for "bits per second" is "bit/s" (not "bits/s", see writing style for SI units The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. It is the world's most widely used system of measurement, both in everyday commerce and in science). In less formal contexts the abbreviations "b/s" or "bps" are often used, though this risks confusion with "bytes The byte is a unit of digital information in computing and telecommunications. It is an ordered collection of bits, in which each bit denotes the binary value of 1 or 0. Historically, a byte was the number of bits (typically 5, 6, 7, 8, 9, or 16) used to encode a single character of text in a computer and it is for this reason the basic per second" ("B/s", "Bps").
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Bit rates at various protocol layers
Physical layer gross bit rate
In digital communication systems, the gross bitrate, raw bitrate, line rate or data signaling rate In telecommunication, data signaling rate , also known as gross bit rate, is the aggregate rate at which data pass a point in the transmission path of a data transmission system is the total number of physically transferred bits per second over a communication link, including useful data as well as protocol overhead. The gross bit rate is related to, but should not be confused with, the baud rate In digital communications, symbol rate, also known as baud or modulation rate; is the number of symbol changes made to the transmission medium per second using a digitally modulated signal or a line code. The Symbol rate is measured in baud (Bd) or symbols/second. In the case of a line code, the symbol rate is the pulse rate in pulses/second. Each in symbols/s or pulses/s. Gross bit rate can be used interchangeably with "baud In telecommunications and electronics, baud is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes (signaling events) made to the transmission medium per second in a digitally modulated signal or a line code. The baud rate is related rate" only when each modulation transition of a data transmission In telecommunications, transmission is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless. Transmission technologies and schemes typically refer to physical layer protocol duties such as system carries exactly one bit of data; something not true for modern modem A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used over any means of transmitting analog modulation systems and modern LANs, for example.
For most line codes and modulation methods:
- Baud rate ≤ Gross bit rate
More specifically, a line code In telecommunication, a line code is a code chosen for use within a communications system for baseband transmission purposes. Line coding is often used for digital data transport representing the data using pulse-amplitude modulation Pulse-amplitude modulation, acronym PAM, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses with 2N different voltage levels, or a digital modulation In electronics, modulation is the process of varying one or more properties of high frequency periodic waveform, called the carrier signal, with respect to a modulating signal. This is done in a similar fashion as a musician may modulate a tone from a musical instrument by varying its volume, timing and pitch. The three key parameters of a method using 2N different symbols, for example 2N amplitudes, phases or frequencies, can transfer N bit/symbol, or N bit/pulse. This results in:
- Gross bit rate = Baud rate · N
The exception from the above is some self-synchronizing line codes, for example Manchester coding In telecommunication, Manchester code is a line code in which the encoding of each data bit has at least one transition and occupies the same time. It is, therefore, self-clocking, which means that a clock signal can be recovered from the encoded data and return-to-zero Return-to-zero describes a line code used in telecommunications signals in which the signal drops (returns) to zero between each pulse. This takes place even if a number of consecutive 0's or 1's occur in the signal. The signal is self-clocking. This means that a separate clock does not need to be sent alongside the signal, but suffers from using (RTZ) coding, where each bit is represented by two pulses (signal states), resulting in:
- Gross bit rate = Baud rate/2
A theoretical upper bound for the baud rate in symbols/s or pulses/s for a certain analog bandwidth Bandwidth is typically measured in hertz, and may sometimes refer to passband bandwidth, sometimes to baseband bandwidth, depending on context. Passband bandwidth is the difference between the upper and lower cutoff frequencies of, for example, an electronic filter, a communication channel, or a signal spectrum. In case of a lowpass filter or in hertz is given by the Nyquist law In signal processing, the Nyquist rate is two times the bandwidth of a bandlimited signal or a bandlimited channel. This term is used to mean two different things under two different circumstances::
- Baud rate ≤ Nyquist rate = 2 · bandwidth
In practice this upper bound can only be approached for line coding schemes (or baseband transmission) and for so-called vestigal sideband digital modulation. Most other digital carrier-modulated schemes (or passband transmission schemes), for example ASK Amplitude-shift keying is a form of modulation that represents digital data as variations in the amplitude of a carrier wave, PSK Phase-shift keying is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave) and QAM Quadrature amplitude modulation (pronounced /ˈkwɑːm/ or /ˈkæm/ or simply "Q-A-M") is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing (modulating) the amplitudes of two carrier waves, using the amplitude-shift keying (ASK) digital modulation scheme or, can be characterized as double sideband modulation, resulting in the following approximative relation:
- Baud rate ≤ Bandwidth
Physical layer net bit rate
The physical layer net bitrate, peak bitrate, useful bit rate, information rate or wire speed (informal language) of a digital communication link is the capacity excluding the physical layer The Physical Layer is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY protocol overhead, for example time division multiplex (TDM) framing bits While receiving a stream of framed data, frame synchronization is the process by which incoming frame alignment signals, i.e., distinctive bit sequences , are identified, i.e., distinguished from data bits, permitting the data bits within the frame to be extracted for decoding or retransmission. This is sometimes referred to as "framing", redundant forward error correction In telecommunication and information theory, forward error correction is a system of error control for data transmission, whereby the sender adds redundant data to its messages, also known as an error-correction code. This allows the receiver to detect and correct errors (within some bound) without the need to ask the sender for additional data (FEC) codes, equalizer training symbols and other channel coding In digital communications, a channel code is a broadly used term mostly referring to the forward error correction code and bit interleaving in communication and storage where the communication media or storage media is viewed as a channel. The channel code is used to protect data sent over it for storage or retrieval even in the presence of noise. Error-correcting codes are common especially in wireless communication systems and broadband modem standards. The relationship between the gross bit rate and net bit rate is affected by the FEC code rate The code rate or information rate of a forward error correction code, for example a convolutional code, states what portion of the total amount of information that is useful (non redundant). The code rate is typically a fractional number. If the code rate is k/n, for every k bits of useful information, the coder generates totally n bits of data, according to the following.
Some operational systems indicate the "connection speed" (informal language) of a network access technology or communication device. The connection speed of a technology that involves forward error correction typically refers to the physical layer net bit rate in accordance with the above definition.
For example, the net bitrate (and thus the "connection speed") of a IEEE 802.11a wireless network is the net bit rate of between 6 and 54 Mbit/s, while the gross bit rate is between 12 and 72 Mbit/s inclusive of error-correcting codes. The net bit rate of ISDN Basic Rate Interface Basic Rate Interface is an Integrated Services Digital Network (ISDN) configuration defined in the physical layer standard I.430 produced by the International Telecommunication Union (ITU). It is one of two configurations for use in the access network, the other being Primary Rate Interface (PRI). The BRI configuration provides two 64 kbit/s (2 B-channels + 1 D-channel) of 64+64+16 = 144 kbit/s also refers to the user data rates, while the line rate is 160 kbit/s.
The net bitrate of the Ethernet 100Base-TX physical layer standard is 100 Mbit/s, while the gross bitrate is 125 Mbit/second, due to the 4B5B In telecommunication, 4B5B is a form of data communications line code. 4B5B maps groups of four bits onto groups of 5 bits, with a minimum density of 1 bits in the output. When NRZI-encoded, the 1 bits provide necessary clock transitions for the receiver. For example, a run of 4 bits such as 0000 contains no transitions and that causes clocking (four bit over five bit) encoding. In this case, the gross bit rate is equal to the symbol rate or pulse rate of 125 Mbaud, due to the NRZI In telecommunication, a non-return-to-zero line code is a binary code in which 1's are represented by one significant condition (usually a positive voltage) and 0's are represented by some other significant condition (usually a negative voltage), with no other neutral or rest condition. The pulses have more energy than a RZ code. Unlike RZ, NRZ line code In telecommunication, a line code is a code chosen for use within a communications system for baseband transmission purposes. Line coding is often used for digital data transport.
In communications technologies without forward error correction and other physical layer protocol overhead, there is no distinction between gross bit rate and physical layer net bit rate. For example, the net as well as gross bit rate of Ethernet 10Base-T is 10 Mbit/s. Due to the Manchester line code, each bit is represented by two pulses, resulting in a pulse rate of 20 Mbaud.
The net bitrate of a V.92 V.92 is an ITU-T recommendation, titled Enhancements to Recommendation V.90, that establishes a modem standard allowing near 56 kbit/s download and 48 kbit/s upload rates. With V.92 PCM is used for both the upstream and downstream connections; previously 56K modems only used PCM for downstream data voiceband In electronics, voiceband means the typical human hearing frequency range that is from 20 Hz to 20 kHz. In telephony, it means the frequency range normally transmitted by a telephone line, generally about 200–3600 Hz. Frequency-division multiplexing in telephony normally uses 4 kHz carrier spacing. The roll-off rate, or rate at which the modem A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used over any means of transmitting analog refers to the gross bit rate, since there is no additional error-correction code. It can be up to 56,000 bit/s downstreams and 48,000 bit/s upstreams. A lower bit rate may be chosen during the connection establishment phase due to adaptive modulation - slower but more robust modulation schemes are chosen in case of poor signal-to-noise ratio Signal-to-noise ratio is a measure used in science and engineering to quantify how much a signal has been corrupted by noise. It is defined as the ratio of signal power to the noise power corrupting the signal. A ratio higher than 1:1 indicates more signal than noise. While SNR is commonly quoted for electrical signals, it can be applied to any.
The channel capacity In electrical engineering, computer science and information theory, channel capacity is the tightest upper bound on the amount of information that can be reliably transmitted over a communications channel. By the noisy-channel coding theorem, the channel capacity of a given channel is the limiting information rate that can be achieved with, also known as the Shannon capacity, is a theoretical upper bound for the maximum net bitrate, exclusive of forward error correction coding, that is possible without bit errors for a certain physical analog node-to-node communication link In telecommunication a data link is the means of connecting one location to another for the purpose of transmitting and receiving digital information. It can also refer to a set of electronics assemblies, consisting of a transmitter and a receiver [two data terminal equipments ] and the interconnecting data telecommunication circuit. These are.
- Net bit rate ≤ Channel capacity
The channel capacity is proportional to the analog bandwidth in hertz. This proportionality is called Hartley's law In information theory, the Shannon–Hartley theorem is an application of the noisy channel coding theorem to the archetypal case of a continuous-time analog communications channel subject to Gaussian noise. The theorem establishes Shannon's channel capacity for such a communication link, a bound on the maximum amount of error-free digital data. Consequently the net bit rate is sometimes called digital bandwidth In computer networking and computer science, digital bandwidth, network bandwidth or just bandwidth is a measure of available or consumed data communication resources expressed in bit/s or multiples of it capacity in bit/s.
Network throughput
The term throughput In communication networks, such as Ethernet or packet radio, throughput or network throughput is the average rate of successful message delivery over a communication channel. This data may be delivered over a physical or logical link, or pass through a certain network node. The throughput is usually measured in bits per second , and sometimes in, essentially the same thing as digital bandwidth In computer networking and computer science, bandwidth, digital bandwidth, or network bandwidth is a measure of available or consumed data communication resources expressed in bit/s or multiples of it consumption, denotes the achieved average useful bit rate in a computer network over a logical or physical communication link or through a network node, typically measured at a reference point above the datalink layer. This implies that the throughput often excludes data link layer protocol overhead. The throughput is affected by the traffic load from the data source in question, as well as from other sources sharing the same network resources.
Goodput (data transfer rate)
Goodput In computer networks, goodput is the application level throughput, i.e. the number of useful bits per unit of time forwarded by the network from a certain source address to a certain destination, excluding protocol overhead, and excluding retransmitted data packets or data transfer rate refers to the achieved average net bit rate that is delivered to the application layer Application Layer is a term used in categorizing protocols and methods in architectural models of computer networking. Both the OSI model and the Internet Protocol Suite define application layers, exclusive of all protocol overhead, data packets retransmissions, etc. For example, in the case of file transfer, the goodput corresponds to the achieved file transfer rate. The file transfer rate in bit/s can be calculated as the file size (in bytes), divided by the file transfer time (in seconds), and multiplied by eight.
As an example, the goodput or data transfer rate of a V.92 voiceband modem is affected by the modem physical layer and data link layer protocols. It is sometimes higher than the physical layer data rate due to V.44 The ITU-T V-Series Recommendations on Data communication over the telephone network specify the protocols that govern approved modem communication standards and interfaces data compression, and sometimes lower due to bit-errors and automatic repeat request retransmissions.
If no data compression is provided by the network equipment or protocols, we have the following relation:
- Goodput ≤ Throughput ≤ Maximum throughput ≤ Net bit rate
for a certain communication path.
Multimedia bit rate
In digital multimedia, bit rate often refers to the number of bits used per unit of playback time to represent a continuous medium such as audio or video after source coding (data compression). The size of a multimedia file in bytes is the product of the bit rate (in bit/s) and the length of the recording (in seconds), divided by eight.
In case of realtime streaming multimedia, this bit rate measure is the goodput that is required to avoid interrupts. For streaming multimedia without interrupts, we have the following relationship:
- Multimedia bit rate = Required goodput
The term average bitrate is used in case of variable bitrate multimedia source coding schemes.
A theoretical lower bound for the multimedia bit rate for lossless data compression is the source information rate, also known as the entropy rate.
- Entropy rate ≤ Multimedia bit rate
Prefixes
When quantifying large bit rates, SI prefixes (also known as Metric prefixes or Decimal prefixes) are used, thus:
| 1,000 bit/s | rate = 1 kbit/s (one kilobit or one thousand bits per second) |
| 1,000,000 bit/s | rate = 1 Mbit/s (one megabit or one million bits per second) |
| 1,000,000,000 bit/s | rate = 1 Gbit/s (one gigabit or one billion bits per second) |
Binary prefixes have almost never been used for bitrates, although they may occasionally be seen when data rates are expressed in bytes per second (byte/s). A 1999 IEC standard (IEC 60027-2) specifies different abbreviations for Binary and Decimal (SI) prefixes, but these are not always adhered to, and therefore sometimes it is necessary to seek clarification of the units used in a particular context.
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