Bit rate
Encyclopedia
In telecommunications and computing
, bit rate (sometimes written bitrate, data rate or as a variable R) is the number of bit
s that are conveyed or processed per unit of time.
The bit rate is quantified using the bits per second
(bit/s or bps) unit, often in conjunction with an SI prefix
such as kilo- (kbit/s or kbps), mega- (Mbit/s or Mbps), giga- (Gbit/s or Gbps) or tera- (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.
The formal abbreviation for "bits per second" is "bit/s" (not "bits/s", see writing style for SI units). In less formal contexts the abbreviations "b/s" or "bps" are often used, though this risks confusion with "byte
s per second" ("B/s", "Bps"). 1 Byte/s (Bps or B/s) corresponds to 8-bit/s (bps or b/s).
gross bitrate, raw bitrate, data signaling rate
gross data transfer rate or uncoded transmission rate (sometimes written as a variable Rb or fb) is the total number of physically transferred bits per second over a communication link, including useful data as well as protocol overhead.
In case of serial communication
s, the gross bit rate is related to the bit transmission time
as:
The gross bit rate is related to, but should not be confused with, the symbol rate
or modulation rate in baud
, symbols/s or pulses/s. Gross bit rate can be used interchangeably with "baud" only when there are two levels or symbols, representing 0 and 1 respectively, meaning that each symbol of a data transmission
system carries exactly one bit of data; something not true for modern modem
modulation systems and modern LANs, for example.
For most line code
s and modulation
methods:
More specifically, a line code (or baseband transmission scheme) representing the data using pulse-amplitude modulation
with 2N different voltage levels, can transfer N bit/pulse. A digital modulation method (or passband transmission scheme) using 2N different symbols, for example 2N amplitudes, phases or frequencies, can transfer N bit/symbol. This results in:
An exception from the above is some self-synchronizing line codes, for example Manchester coding and return-to-zero
(RTZ) coding, where each bit is represented by two pulses (signal states), resulting in:
A theoretical upper bound for the symbol rate in baud, symbols/s or pulses/s for a certain spectral bandwidth in hertz is given by the Nyquist law
:
In practice this upper bound can only be approached for line coding schemes and for so-called vestigal sideband digital modulation. Most other digital carrier-modulated schemes, for example ASK
, PSK
, QAM
and OFDM, can be characterized as double sideband modulation, resulting in the following relation:
In case of parallel communication
, the gross bit rate is given by
where n is the number of parallel channels, Mi is the number of symbols or levels of the modulation
in the i-th channel
, and Ti is the symbol duration time, expressed in seconds, for the i-th channel.
net bitrate, information rate, useful bit rate, payload rate, net data transfer rate, coded transmission rate, effective data rate or wire speed
(informal language) of a digital communication channel is the capacity excluding the physical layer
protocol overhead, for example time division multiplex (TDM) framing bits, redundant forward error correction
(FEC) codes, equalizer training symbols and other channel coding. Error-correcting codes are common especially in wireless communication systems, broadband modem standards and modern cupper-based high-speed LANs. The physical layer net bitrate is the datarate measured at a reference point in the interface between the datalink layer and physical layer, and may consequently include data link and higher layer overhead.
In modems and wireless systems, link adaptation
(automatic adaption of the data rate and the modulation and/or error coding scheme to the signal quality) is often applied. In that context, the term peak bitrate denotes the net bitrate of the fastest and least robust transmission mode, used for example when the distance is very short between sender and transmitter. Some operating systems and network equipment may detect the "connection speed" (informal language) of a network access technology or communication device, implying the current net bit rate. Note that the term line rate in some textbooks is defined as gross bit rate, in others as net bit rate.
The relationship between the gross bit rate and net bit rate is affected by the FEC code rate
according to the following.
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
(2 B-channels + 1 D-channel) of 64+64+16 = 144 kbit/s also refers to the payload data rates, while the signalling rate is 160 kbit/s.
The net bit rate of the Ethernet 100Base-TX physical layer standard is 100 Mbit/s, while the gross bitrate is 125 Mbit/second, due to the 4B5B
(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 line code
.
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 "connection speed" of a V.92
voiceband
modem
typically 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
. Due to data compression, the actual data transmission rate or throughput (see below) may be higher.
The channel capacity
, 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.
The channel capacity is proportional to the analog bandwidth in hertz. This proportionality is called Hartley's law. Consequently the net bit rate is sometimes called digital bandwidth capacity in bit/s.
, essentially the same thing as digital bandwidth
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. See also Measuring network throughput
.
or data transfer rate refers to the achieved average net bit rate that is delivered to the application layer
, 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 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:
for a certain communication path.
, 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 encoding bit rate of a multimedia file is the size of a multimedia file in bytes divided by the playback time of the recording (in seconds), multiplied by eight.
For realtime streaming multimedia, the encoding bit rate is the goodput
that is required to avoid interrupt:
The term average bitrate
is used in case of variable bitrate
multimedia source coding schemes. In this context, the peak bit rate is the maximum number of bits required for any short-term block of compressed data.
A theoretical lower bound for the encoding bit rate for lossless data compression
is the source information rate, also known as the entropy rate.
es (also known as Metric prefixes or Decimal prefixes) are used, thus:
Binary prefix
es have almost never been used for bitrates, although they may occasionally be seen when data rates are expressed in bytes per second (e.g. 1 kByte/s or kBps is sometimes interpreted as 1000 Byte/s, sometimes as 1024 Byte/s). A 1999 IEC standard (IEC 60027-2) specifies different abbreviations for Binary and Decimal (SI) prefixes (e.g. 1 kiB
/s = 1024 Byte/s = 8192-bit/s, and 1 MiB
/s = 1024 kiB/s), but these are still not very common in the literature, and therefore sometimes it is necessary to seek clarification of the units used in a particular context.
For more examples, see List of device bit rates, Spectral efficiency comparison table and OFDM system comparison table.
Generally, choices are made about the above factors in order to achieve the desired trade-off between minimizing the bitrate and maximizing the quality of the material when it is played.
If lossy data compression
is used on audio or visual data, differences from the original signal will be introduced; if the compression is substantial, or lossy data is decompressed and recompressed, this may become noticeable in the form of compression artifact
s. Whether these affect the perceived quality, and if so how much, depends on the compression scheme, encoder power, the characteristics of the input data, the listener’s perceptions, the listener's familiarity with artifacts, and the listening or viewing environment.
The bitrates in this section are approximately the minimum that the average listener in a typical listening or viewing environment, when using the best available compression, would perceive as not significantly worse than the reference standard:
2 channels, 1-bit, 2822.4 kHz DSD audio (2x1x2,822,400)= 5,644,800bits/s
Computing
Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...
, bit rate (sometimes written bitrate, data rate or as a variable R) is the number of bit
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
s that are conveyed or processed per unit of time.
The bit rate is quantified using the bits per second
Data rate units
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 unit bit per second or byte per second.- Avoiding confusion :To be as...
(bit/s or bps) unit, often in conjunction with an SI prefix
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 decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol...
such as kilo- (kbit/s or kbps), mega- (Mbit/s or Mbps), giga- (Gbit/s or Gbps) or tera- (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.
The formal abbreviation for "bits per second" is "bit/s" (not "bits/s", see writing style for SI units). In less formal contexts the abbreviations "b/s" or "bps" are often used, though this risks confusion with "byte
Byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
s per second" ("B/s", "Bps"). 1 Byte/s (Bps or B/s) corresponds to 8-bit/s (bps or b/s).
Gross bit rate
In digital communication systems, the physical layerPhysical layer
The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....
gross bitrate, raw bitrate, data signaling rate
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.Notes:#The DSR is usually expressed in bits per second....
gross data transfer rate or uncoded transmission rate (sometimes written as a variable Rb or fb) is the total number of physically transferred bits per second over a communication link, including useful data as well as protocol overhead.
In case of serial communication
Serial communication
In telecommunication and computer science, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are sent as a whole, on a link with several parallel channels...
s, the gross bit rate is related to the bit transmission time
as:
The gross bit rate is related to, but should not be confused with, the symbol rate
Symbol rate
In digital communications, symbol 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 or symbols/second. In the case of a line code, the symbol rate is the pulse rate in pulses/second...
or modulation rate in baud
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 made to the transmission medium per second in a digitally modulated signal or a...
, symbols/s or pulses/s. Gross bit rate can be used interchangeably with "baud" only when there are two levels or symbols, representing 0 and 1 respectively, meaning that each symbol of a data transmission
Data transmission
Data transmission, digital transmission, or digital communications is the physical transfer of data over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibres, wireless communication channels, and storage media...
system carries exactly one bit of data; something not true for modern modem
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...
modulation systems and modern LANs, for example.
For most line code
Line code
In telecommunication, a line code is a code chosen for use within a communications system for baseband transmission purposes...
s and modulation
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
methods:
- Symbol rate ≤ Gross bit rate
More specifically, a line code (or baseband transmission scheme) representing the data using pulse-amplitude modulation
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, can transfer N bit/pulse. A digital modulation method (or passband transmission scheme) using 2N different symbols, for example 2N amplitudes, phases or frequencies, can transfer N bit/symbol. This results in:
- Gross bit rate = Symbol rate · N
An exception from the above is some self-synchronizing line codes, for example Manchester coding and return-to-zero
Return-to-zero
For the Delp/Goudreau band, see RTZReturn-to-zero describes a line code used in telecommunications signals in which the signal drops 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...
(RTZ) coding, where each bit is represented by two pulses (signal states), resulting in:
- Gross bit rate = Symbol rate/2
A theoretical upper bound for the symbol rate in baud, symbols/s or pulses/s for a certain spectral bandwidth in hertz is given by the Nyquist law
Nyquist rate
In signal processing, the Nyquist rate, named after Harry Nyquist, is two times the bandwidth of a bandlimited signal or a bandlimited channel...
:
- Symbol rate ≤ Nyquist rate = 2 · bandwidth
In practice this upper bound can only be approached for line coding schemes and for so-called vestigal sideband digital modulation. Most other digital carrier-modulated schemes, for example ASK
Amplitude-shift keying
Amplitude-shift keying is a form of modulation that represents digital data as variations in the amplitude of a carrier wave.Any digital modulation scheme uses a finite number of distinct signals to represent digital data. ASK uses a finite number of amplitudes, each assigned a unique pattern of...
, PSK
Phase-shift keying
Phase-shift keying is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal ....
, QAM
Quadrature amplitude modulation
Quadrature amplitude modulation is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing the amplitudes of two carrier waves, using the amplitude-shift keying digital modulation scheme or amplitude modulation analog...
and OFDM, can be characterized as double sideband modulation, resulting in the following relation:
- Symbol rate ≤ Bandwidth
In case of parallel communication
Parallel port
A parallel port is a type of interface found on computers for connecting various peripherals. In computing, a parallel port is a parallel communication physical interface. It is also known as a printer port or Centronics port...
, the gross bit rate is given by
where n is the number of parallel channels, Mi is the number of symbols or levels of the modulation
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
in the i-th channel
Channel (communications)
In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel...
, and Ti is the symbol duration time, expressed in seconds, for the i-th channel.
Information rate
The physical layerPhysical layer
The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....
net bitrate, information rate, useful bit rate, payload rate, net data transfer rate, coded transmission rate, effective data rate or wire speed
Wire speed
Wire speed or wirespeed is a non-formal language term referring to the hypothetical peak physical layer net bitrate of a cable combined with a certain digital communication device/interface/port...
(informal language) of a digital communication channel is the capacity excluding the physical layer
Physical layer
The physical layer or layer 1 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, redundant forward error correction
Forward error correction
In telecommunication, information theory, and coding theory, forward error correction or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels....
(FEC) codes, equalizer training symbols and other channel coding. Error-correcting codes are common especially in wireless communication systems, broadband modem standards and modern cupper-based high-speed LANs. The physical layer net bitrate is the datarate measured at a reference point in the interface between the datalink layer and physical layer, and may consequently include data link and higher layer overhead.
In modems and wireless systems, link adaptation
Link adaptation
Link adaptation, or adaptive coding and modulation , is a term used in wireless communications to denote the matching of the modulation, coding and other signal and protocol parameters to the conditions on the radio link Link adaptation, or adaptive coding and modulation (ACM), is a term used in...
(automatic adaption of the data rate and the modulation and/or error coding scheme to the signal quality) is often applied. In that context, the term peak bitrate denotes the net bitrate of the fastest and least robust transmission mode, used for example when the distance is very short between sender and transmitter. Some operating systems and network equipment may detect the "connection speed" (informal language) of a network access technology or communication device, implying the current net bit rate. Note that the term line rate in some textbooks is defined as gross bit rate, in others as net bit rate.
The relationship between the gross bit rate and net bit rate is affected by the FEC code rate
Code rate
In telecommunication and information theory, the code rate of a forward error correction code is the proportion of the data-stream that is useful...
according to the following.
- Net bit rate ≤ Gross bit rate · code rateCode rateIn telecommunication and information theory, the code rate of a forward error correction code is the proportion of the data-stream that is useful...
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
Basic Rate Interface is an Integrated Services Digital Network configuration intended primarily for use in subscriber lines similar to those that have long been used for plain old telephone service...
(2 B-channels + 1 D-channel) of 64+64+16 = 144 kbit/s also refers to the payload data rates, while the signalling rate is 160 kbit/s.
The net bit rate of the Ethernet 100Base-TX physical layer standard is 100 Mbit/s, while the gross bitrate is 125 Mbit/second, due to the 4B5B
4B5B
In telecommunication, 4B5B is a form of data communications Block Coding. 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...
(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 line code
Line code
In telecommunication, a line code is a code chosen for use within a communications system for baseband transmission purposes...
.
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
Manchester code
In telecommunication and data storage, Manchester code is a line code in which the encoding of each data bit has at least one transition and occupies the same time...
line code, each bit is represented by two pulses, resulting in a pulse rate of 20 Mbaud.
The "connection speed" of a V.92
V.92
V.92 is an ITU-T recommendation, titled Enhancements to Recommendation V.90, that establishes a modem standard allowing near 56 kb/s download and 48 kb/s upload rates. With V.92 PCM is used for both the upstream and downstream connections; previously 56K modems only used PCM for downstream...
voiceband
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...
modem
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...
typically refers to the gross bit rate, since there is no additional error-correction code. It can be up to 56,000-bit/s downstreams
Downstream (computer science)
In a telecommunications network or computer network, downstream refers to data sent from a network service provider to a customer.Although the best voiceband modems are called 56 kbit/s modems, downstream speeds can be limited to a few tens of kilobits per second with even lower upstream speeds...
and 48,000-bit/s upstreams
Upstream (networking)
In computer networking, upstream refers to the direction in which data can be transferred from the client to the server . This differs greatly from downstream not only in theory and usage, but also in that upstream speeds are usually at a premium...
. 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
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
. Due to data compression, the actual data transmission rate or throughput (see below) may be higher.
The channel capacity
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...
, also known as the Shannon
Shannon–Hartley theorem
In information theory, the Shannon–Hartley theorem tells the maximum rate at which information can be transmitted over a communications channel of a specified bandwidth in the presence of noise. It is an application of the noisy channel coding theorem to the archetypal case of a continuous-time...
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.
- Net bit rate ≤ Channel capacity
The channel capacity is proportional to the analog bandwidth in hertz. This proportionality is called Hartley's law. Consequently the net bit rate is sometimes called digital bandwidth capacity in bit/s.
Network throughput
The term throughputThroughput
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...
, essentially the same thing as digital bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
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. See also Measuring network throughput
Measuring network throughput
Throughput of a network can be measured using various tools available on different platforms. This page explains the theory behind what these tools set out to measure and the issues regarding these measurements.-Reasons for measuring throughput in networks:...
.
Goodput (data transfer rate)
GoodputGoodput
In computer networks, goodput is the application level throughput, i.e. the number of useful information bits, delivered by the network to a certain destination, per unit of time. The amount of data considered excludes protocol overhead bits as well as retransmitted data packets...
or data transfer rate refers to the achieved average net bit rate that is delivered to the application layer
Application layer
The Internet protocol suite and the Open Systems Interconnection model of computer networking each specify a group of protocols and methods identified by the name application layer....
, 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 data compression
Data compression
In computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....
, 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 encoding
In digital multimediaMultimedia
Multimedia is media and content that uses a combination of different content forms. The term can be used as a noun or as an adjective describing a medium as having multiple content forms. The term is used in contrast to media which use only rudimentary computer display such as text-only, or...
, 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
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
after source coding
Source coding
In information theory, Shannon's source coding theorem establishes the limits to possible data compression, and the operational meaning of the Shannon entropy....
(data compression). The encoding bit rate of a multimedia file is the size of a multimedia file in bytes divided by the playback time of the recording (in seconds), multiplied by eight.
For realtime streaming multimedia, the encoding bit rate is the goodput
Goodput
In computer networks, goodput is the application level throughput, i.e. the number of useful information bits, delivered by the network to a certain destination, per unit of time. The amount of data considered excludes protocol overhead bits as well as retransmitted data packets...
that is required to avoid interrupt:
- Encoding bit rate = Required goodput
The term average bitrate
Average bitrate
Average bitrate refers to the average amount of data transferredper unit of time, usually measured per second. This is commonly referred to for digital music or video. An MP3 file, for example, that has an average bit rate of 128 kbit/s transfers, on average, 128,000 bits every second...
is used in case of variable bitrate
Variable bitrate
Variable bitrate is a term used in telecommunications and computing that relates to the bitrate used in sound or video encoding. As opposed to constant bitrate , VBR files vary the amount of output data per time segment...
multimedia source coding schemes. In this context, the peak bit rate is the maximum number of bits required for any short-term block of compressed data.
A theoretical lower bound for the encoding bit rate for lossless data compression
Lossless data compression
Lossless data compression is a class of data compression algorithms that allows the exact original data to be reconstructed from the compressed data. The term lossless is in contrast to lossy data compression, which only allows an approximation of the original data to be reconstructed, in exchange...
is the source information rate, also known as the entropy rate.
- Entropy rate ≤ Multimedia bit rate
Prefixes
When quantifying large bit rates, SI prefixSI 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 decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol...
es (also known as Metric prefixes or Decimal prefixes) are used, thus:
| 1,000-bit/s | rate = 1 kbit/s (one kilobit Kilobit The kilobit is a multiple of the unit bit for digital information or computer storage. The prefix kilo is defined in the International System of Units as a multiplier of 103 , and therefore,... or one thousand bits per second) |
| 1,000,000-bit/s | rate = 1 Mbit/s (one megabit Megabit The megabit is a multiple of the unit bit for digital information or computer storage. The prefix mega is defined in the International System of Units as a multiplier of 106 , and therefore... or one million Million One million or one thousand thousand, is the natural number following 999,999 and preceding 1,000,001. The word is derived from the early Italian millione , from mille, "thousand", plus the augmentative suffix -one.In scientific notation, it is written as or just 106... bits per second) |
| 1,000,000,000-bit/s | rate = 1 Gbit/s (one gigabit Gigabit The gigabit is a multiple of the unit bit for digital information or computer storage. The prefix giga is defined in the International System of Units as a multiplier of 109 , and therefore... or one billion 1000000000 (number) 1,000,000,000 is the natural number following 999,999,999 and preceding 1,000,000,001.In scientific notation, it is written as 109.... bits per second) |
Binary prefix
Binary prefix
In computing, a binary prefix is a specifier or mnemonic that is prepended to the units of digital information, the bit and the byte, to indicate multiplication by a power of 2...
es have almost never been used for bitrates, although they may occasionally be seen when data rates are expressed in bytes per second (e.g. 1 kByte/s or kBps is sometimes interpreted as 1000 Byte/s, sometimes as 1024 Byte/s). A 1999 IEC standard (IEC 60027-2) specifies different abbreviations for Binary and Decimal (SI) prefixes (e.g. 1 kiB
Kibibyte
The kibibyte is a multiple of the unit byte for quantities of digital information. The binary prefix kibi means 1024; therefore, 1 kibibyte is . The unit symbol for the kibibyte is KiB. The unit was established by the International Electrotechnical Commission in 1999 and has been accepted for use...
/s = 1024 Byte/s = 8192-bit/s, and 1 MiB
Mebibyte
The mebibyte is a multiple of the unit byte for digital information. The binary prefix mebi means 220, therefore 1 mebibyte is . The unit symbol for the mebibyte is MiB. The unit was established by the International Electrotechnical Commission in 2000 and has been accepted for use by all major...
/s = 1024 kiB/s), but these are still not very common in the literature, and therefore sometimes it is necessary to seek clarification of the units used in a particular context.
Progress trends
These are examples of physical layer net bit rates in proposed communication standard interfaces and devices:| WAN modem 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... s |
Ethernet Ethernet Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies.... LAN |
WiFi WIFI WIFI is a radio station broadcasting a brokered format. Licensed to Florence, New Jersey, USA, the station is currently operated by Florence Broadcasting Partners, LLC.This station was previously owned by Real Life Broadcasting... WLAN |
Mobile data Comparison of mobile phone standards -Issues:Global System for Mobile Communications and IS-95 were the two most prevalent 2G mobile communication technologies in 2007... |
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10BASE5 10BASE5 was the original commercially available variant of Ethernet.For its physical layer it used cable similar to RG-8/U coaxial cable but with extra braided shielding. This is a stiff, diameter cable with an impedance of 50 ohms , a solid center conductor, a foam insulating filler, a shielding... (coax) 10BASE-T Ethernet over twisted pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. Other Ethernet cable standards employ coaxial cable or optical fiber. Early versions developed in the 1980s included StarLAN followed by 10BASE-T. By the 1990s, fast, inexpensive... (twisted pair Twisted pair Twisted pair cabling is a type of wiring in which two conductors are twisted together for the purposes of canceling out electromagnetic interference from external sources; for instance, electromagnetic radiation from unshielded twisted pair cables, and crosstalk between neighboring pairs... ) Fast Ethernet In computer networking, Fast Ethernet is a collective term for a number of Ethernet standards that carry traffic at the nominal rate of 100 Mbit/s, against the original Ethernet speed of 10 Mbit/s. Of the fast Ethernet standards 100BASE-TX is by far the most common and is supported by the... Gigabit Ethernet Gigabit Ethernet is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second , as defined by the IEEE 802.3-2008 standard. It came into use beginning in 1999, gradually supplanting Fast Ethernet in wired local networks where it performed... 10 Gigabit Ethernet The 10 gigabit Ethernet computer networking standard was first published in 2002. It defines a version of Ethernet with a nominal data rate of 10 Gbit/s , ten times faster than gigabit Ethernet.10 gigabit Ethernet defines only full duplex point to point links which are generally connected by... 100 Gigabit Ethernet 40 Gigabit Ethernet, or 40GbE, and 100 Gigabit Ethernet, or 100GbE, are high-speed computer network standards developed by the Institute of Electrical and Electronics Engineers . They support sending Ethernet frames at 40 and 100 gigabits per second over multiple 10 Gbit/s or 25 Gbit/s lanes... |
IEEE 802.11 IEEE 802.11 is a set of standards for implementing wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee . The base version of the standard IEEE 802.11-2007 has had subsequent... 2 Mbit/s IEEE 802.11 IEEE 802.11 is a set of standards for implementing wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee . The base version of the standard IEEE 802.11-2007 has had subsequent... 11 Mbit/s IEEE 802.11 IEEE 802.11 is a set of standards for implementing wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee . The base version of the standard IEEE 802.11-2007 has had subsequent... 54 Mbit/s IEEE 802.11 IEEE 802.11 is a set of standards for implementing wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee . The base version of the standard IEEE 802.11-2007 has had subsequent... 54 Mbit/s IEEE 802.11 IEEE 802.11 is a set of standards for implementing wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee . The base version of the standard IEEE 802.11-2007 has had subsequent... 600 Mbit/s |
1G 1G refers to the first-generation of wireless telephone technology, mobile telecommunications. These are the analog telecommunications standards that were introduced in the 1980s and continued until being replaced by 2G digital telecommunications... :
2G 2G is short for second-generation wireless telephone technology. Second generation 2G cellular telecom networks were commercially launched on the GSM standard in Finland by Radiolinja in 1991... :
3G 3G or 3rd generation mobile telecommunications is a generation of standards for mobile phones and mobile telecommunication services fulfilling the International Mobile Telecommunications-2000 specifications by the International Telecommunication Union... :
See also Comparison of mobile phone standards Comparison of mobile phone standards -Issues:Global System for Mobile Communications and IS-95 were the two most prevalent 2G mobile communication technologies in 2007... |
For more examples, see List of device bit rates, Spectral efficiency comparison table and OFDM system comparison table.
Multimedia
In digital multimedia, bitrate represents the amount of information, or detail, that is stored per unit of time of a recording. The bitrate depends on several factors:- The original material may be sampled at different frequencies
- The samples may use different numbers of bits
- The data may be encoded by different schemes
- The information may be digitally compressedData compressionIn computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....
by different algorithms or to different degrees
Generally, choices are made about the above factors in order to achieve the desired trade-off between minimizing the bitrate and maximizing the quality of the material when it is played.
If lossy data compression
Lossy data compression
In information technology, "lossy" compression is a data encoding method that compresses data by discarding some of it. The procedure aims to minimize the amount of data that need to be held, handled, and/or transmitted by a computer...
is used on audio or visual data, differences from the original signal will be introduced; if the compression is substantial, or lossy data is decompressed and recompressed, this may become noticeable in the form of compression artifact
Compression artifact
A compression artifact is a noticeable distortion of media caused by the application of lossy data compression....
s. Whether these affect the perceived quality, and if so how much, depends on the compression scheme, encoder power, the characteristics of the input data, the listener’s perceptions, the listener's familiarity with artifacts, and the listening or viewing environment.
The bitrates in this section are approximately the minimum that the average listener in a typical listening or viewing environment, when using the best available compression, would perceive as not significantly worse than the reference standard:
MP3
- 32 kbit/s.
- 96 kbit/s.
- 100–160 kbit/s – Standard Bitrate quality; difference can sometimes be obvious (e.g. lack of low frequency quality and high frequency "swashy" effects.)
- 192 kbit/s is the highest level supported by most MP3 encoders when ripping from a Compact Disc.
- 224–320 kbit/s – VBRVariable bitrateVariable bitrate is a term used in telecommunications and computing that relates to the bitrate used in sound or video encoding. As opposed to constant bitrate , VBR files vary the amount of output data per time segment...
to highest MP3MP3MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...
quality.
Other audio
- 800-bit/s – minimum necessary for recognizable speech (using special-purpose FS-1015FS-1015FS-1015 is a secure telephony speech encoding standard developed by the United States Department of Defense and later by NATO. It is also known as LPC-10 and STANAG 4198....
speech codecsSpeech encodingSpeech coding is the application of data compression of digital audio signals containing speech. Speech coding uses speech-specific parameter estimation using audio signal processing techniques to model the speech signal, combined with generic data compression algorithms to represent the resulting...
.) - 1400 bit/s – lowest bitrate open-source speech codec Codec2
- 2.15 kbit/s – minimum bitrate available through the open-source SpeexSpeexSpeex is a patent-free audio compression format designed for speech and also a free software speech codec that may be used on VoIP applications and podcasts. It is based on the CELP speech coding algorithm. Speex claims to be free of any patent restrictions and is licensed under the revised BSD...
codec. - 8 kbit/s – telephoneTelephoneThe telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
quality (using speech codecs.) - 32-500 kbit/s – lossy audio as used in Ogg Vorbis.
- 256 kbit/s – Digital Audio Broadcasting (DABDigital audio broadcastingDigital Audio Broadcasting is a digital radio technology for broadcasting radio stations, used in several countries, particularly in Europe. As of 2006, approximately 1,000 stations worldwide broadcast in the DAB format....
.) MP2MPEG-1 Audio Layer IIMPEG-1 Audio Layer II or MPEG-2 Audio Layer II is a lossy audio compression format defined by ISO/IEC 11172-3 alongside MPEG-1 Audio Layer I and MPEG-1 Audio Layer III...
bit rate required to achieve a high quality signal. - 400 kbit/s–1,411kbit/s – lossless audio as used in formats such as Free Lossless Audio Codec, WavPackWavPackWavPack is a free, open source lossless audio compression format developed by David Bryant.-Features:WavPack compression can compress 8-, 16-, 24-, and 32-bit fixed-point, and 32-bit floating point audio files in the .WAV file format. It also supports surround sound streams and high frequency...
or Monkey's AudioMonkey's AudioMonkey's Audio is a file format for audio data compression. Being a lossless format, Monkey's Audio does not discard data during the process of encoding, unlike lossy compression methods such as AAC, MP3, Vorbis and Musepack....
to compress CD audio. - 1,411.2 kbit/s – Linear PCM sound format of Compact Disc Digital Audio.
- 5,644.8 kbit/s – DSDDirect Stream DigitalDirect-Stream Digital is the trademark name used by Sony and Philips for their system of recreating audible signals which uses pulse-density modulation encoding, a technology to store audio signals on digital storage media which is used for the Super Audio CD .The signal is stored as delta-sigma...
(A trademarked implementation of PDMPulse-density modulationPulse-density modulation, or PDM, is a form of modulation used to represent an analog signal with digital data. In a PDM signal, specific amplitude values are not encoded into pulses of different size as they would be in PCM. Instead, it is the relative density of the pulses that corresponds to...
) sound format of Super Audio CDSuper Audio CDSuper Audio CD is a high-resolution, read-only optical disc for audio storage. Sony and Philips Electronics jointly developed the technology, and publicized it in 1999. It is designated as the Scarlet Book standard. Sony and Philips previously collaborated to define the Compact Disc standard...
.
2 channels, 1-bit, 2822.4 kHz DSD audio (2x1x2,822,400)= 5,644,800bits/s
Video
- 16 kbit/s – videophoneVideophoneA videophone is a telephone with a video screen, and is capable of full duplex video and audio transmissions for communication between people in real-time...
quality (minimum necessary for a consumer-acceptable "talking head" picture using various video compression schemes) - 128 – 384 kbit/s – business-oriented videoconferencingVideoconferencingVideoconferencing is the conduct of a videoconference by a set of telecommunication technologies which allow two or more locations to interact via two-way video and audio transmissions simultaneously...
quality using video compression - 1.15 Mbit/s max – VCDVCDVCD is a three-letter abbreviation with multiple meanings, as described below:* VCD Athletic, semi-professional football team* Video CD* Voice command device* Value change dump * Vocal cord dysfunction* Visual Communication and Design...
quality (using MPEG1MPEG-1MPEG-1 is a standard for lossy compression of video and audio. It is designed to compress VHS-quality raw digital video and CD audio down to 1.5 Mbit/s without excessive quality loss, making video CDs, digital cable/satellite TV and digital audio broadcasting possible.Today, MPEG-1 has become...
compression) - 3.5 Mbit/s typ - Standard-definition televisionStandard-definition televisionSorete-definition television is a television system that uses a resolution that is not considered to be either enhanced-definition television or high-definition television . The term is usually used in reference to digital television, in particular when broadcasting at the same resolution as...
quality (with bit-rate reduction from MPEG-2 compression) - 9.8 Mbit/s max – DVDDVDA DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
(using MPEG2 compression) - 8 to 15 Mbit/s typ – HDTVHigh-definition televisionHigh-definition television is video that has resolution substantially higher than that of traditional television systems . HDTV has one or two million pixels per frame, roughly five times that of SD...
quality (with bit-rate reduction from MPEG-4 AVC compression) - 19 Mbit/s approximate - HDVHDVHDV is a format for recording of high-definition video on DV cassette tape. The format was originally developed by JVC and supported by Sony, Canon and Sharp...
720p (using MPEG2 compression) - 24 Mbit/s max - AVCHDAVCHDAVCHD is a file-based format for the digital recording and playback of high-definition video....
(using MPEG4 AVCH.264/MPEG-4 AVCH.264/MPEG-4 Part 10 or AVC is a standard for video compression, and is currently one of the most commonly used formats for the recording, compression, and distribution of high definition video...
compression) - 25 Mbit/s approximate - HDVHDVHDV is a format for recording of high-definition video on DV cassette tape. The format was originally developed by JVC and supported by Sony, Canon and Sharp...
1080i (using MPEG2 compression) - 29.4 Mbit/s max – HD DVDHD DVDHD DVD is a discontinued high-density optical disc format for storing data and high-definition video.Supported principally by Toshiba, HD DVD was envisioned to be the successor to the standard DVD format...
- 40 Mbit/s max – Blu-ray DiscBlu-ray DiscBlu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...
(using MPEG2, AVCH.264/MPEG-4 AVCH.264/MPEG-4 Part 10 or AVC is a standard for video compression, and is currently one of the most commonly used formats for the recording, compression, and distribution of high definition video...
or VC-1VC-1VC-1 is the informal name of the SMPTE 421M video codec standard, which was initially developed as a proprietary video format by Microsoft before it was released as a formal SMPTE standard video format on April 3, 2006...
compression)
See also
- AC3
- Audio bit depthAudio bit depthIn digital audio, bit depth describes the number of bits of information recorded for each sample. Bit depth directly corresponds to the resolution of each sample in a set of digital audio data...
- Average bitrateAverage bitrateAverage bitrate refers to the average amount of data transferredper unit of time, usually measured per second. This is commonly referred to for digital music or video. An MP3 file, for example, that has an average bit rate of 128 kbit/s transfers, on average, 128,000 bits every second...
- Bandwidth (computing)Bandwidth (computing)In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
- BaudBaudIn 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 made to the transmission medium per second in a digitally modulated signal or a...
(symbol rate) - Clock rateClock rateThe clock rate typically refers to the frequency that a CPU is running at.For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry into a corresponding square wave...
- Code rateCode rateIn telecommunication and information theory, the code rate of a forward error correction code is the proportion of the data-stream that is useful...
- Constant bitrateConstant bitrateConstant bitrate is a term used in telecommunications, relating to the quality of service. Compare with variable bitrate.When referring to codecs, constant bit rate encoding means that the rate at which a codec's output data should be consumed is constant...
- Data rate unitsData rate unitsIn 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 unit bit per second or byte per second.- Avoiding confusion :To be as...
- Data signaling rateData signaling rateIn 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.Notes:#The DSR is usually expressed in bits per second....
- List of device bit rates
- Measuring network throughputMeasuring network throughputThroughput of a network can be measured using various tools available on different platforms. This page explains the theory behind what these tools set out to measure and the issues regarding these measurements.-Reasons for measuring throughput in networks:...
- Spectral efficiencySpectral efficiencySpectral efficiency, spectrum efficiency or bandwidth efficiency refers to the information rate that can be transmitted over a given bandwidth in a specific communication system...
- Variable bitrateVariable bitrateVariable bitrate is a term used in telecommunications and computing that relates to the bitrate used in sound or video encoding. As opposed to constant bitrate , VBR files vary the amount of output data per time segment...
External links
- DVD-HQ bitrate calculator Calculate bitrate for various types of digital video media.
- Maximum PC - Do Higher MP3 Bit Rates Pay Off?