Data transfer rate

The data transfer rate (also known as data transfer rate , data rate ) describes the amount of digital data that is transferred over a transmission channel within a period of time . The terms data transmission speed , transmission speed and connection speed are also used synonymously . Since the smallest unit of the data volume is the bit , the transmission rate is often referred to as the bit rate .

Not linguistically exact, since the terms stand for related, but actually different quantities, are bandwidth or capacity . A distinction must also be made between the data throughput , in which only the pure user data are taken into account, whereas the data transmission rate also includes any control data.

The maximum possible data transmission rate that can be transmitted over a channel without errors is referred to as the channel capacity . Together with the latency (response delay), it is a measure of the performance of a channel. A channel can be, for example, a connection in the computer network , the connection to the Internet service provider or the interface to a data store .

Measures of the data transfer rate

The data transfer rate (C) is calculated from the amount of data (D) per time period (t):

${\ displaystyle C = {\ frac {D} {t}}}$

The amount of data is measured in bits , the time in seconds . This results in the unit of bit per second ( bit / s or bit / s , formerly b / s ) or English bits per second ( bps ) for the data transmission rate . Larger values ​​are given in multiples and provided with SI unit prefixes:

• kilobits per second ( kbit / s or kbps )
• Megabits per second ( Mbit / s or Mbps )
• Gigabit per second ( Gbit / s or Gbps )

Important here: For data transmission rates, the unit prefixes are used in their SI-compliant decimal meaning and not as binary prefixes . 1 kbit / s is therefore 1,000 bit / s and not 1,024 bit / s. For example, a Gigabit Ethernet at 125  Mbaud uses the 5-PAM modulation method with 2 bits per symbol and wire pair over four wire pairs 1,000,000,000 bit / s. The same applies to data rates for audio signals: An audio CD with a sampling rate of 44.1 kHz with two channels with 16 bit each has a data transfer rate of 1,411,200 bit / s, which corresponds to the commonly specified 1,411 kbit / s. And also with MP3 : 128 kbit / s = 128,000 bit / s.

In areas in which parallel data transmission is used (especially when accessing data memories via a data bus ), the transmission rate is also often specified in bytes per second (byte / s, Bps for short ), which is usually a multiple of 8 bits per second are meant; you have to pay attention to whether a transmission rate z. B. is specified with 1 MB / s or with 1 Mbit / s (the former is exactly eight times the speed of the latter). A specification in baud , however, is wrong, because that is the unit for the step speed or symbol rate (baud rate).

With a given value, it is often unclear at which point or which protocol level this data rate is achieved and which data rate is actually available to the user. For example, with USB 2.0 Hi-Speed ​​with a nominal speed of 480 Mbit / s, only about 300 Mbit / s can be used for transmission. With Ethernet , the specified data rate always relates to the MAC level ; the physical data rate can be much higher depending on the line code . With Fiber Channel , the (rounded) physical data rate is always specified; 20% less (up to 8 Gbit / s) can actually be used, as is the case with Serial ATA and Serial Attached SCSI .

Relationship between data transfer rate, bandwidth and walking speed

The channel capacity (maximum data transfer rate), bandwidth and step speed are interrelated. This relationship is described by the Shannon-Hartley law and is also referred to as the communications cuboid in communications engineering. For a transmission channel with bandwidth B and signal-to-noise ratio SNR with additive white noise , the maximum achievable, error-free data transmission rate C has the following relationship:

${\ displaystyle C = B \ cdot \ log _ {2} (1 + {\ text {SNR}})}$

This means that both the bandwidth and the signal-to-noise ratio influence the channel capacity. A predetermined data transmission rate can be achieved both in a transmission channel with a large signal-to-noise ratio and a small bandwidth and in one with a lower signal-to-noise ratio but a correspondingly larger bandwidth.

It is essential that this law only applies to white noise whose amplitudes are normally distributed . This noise is also known as additive white Gaussian noise referred to in English additive white Gaussian noise or AWGN . Transmission channels that only have this interference and can be characterized with the above equation are therefore also referred to as AWGN channels . This relationship no longer applies to interference signals with a different distribution of the noise spectrum. However, since the normal distribution has the maximum differential entropy , WGN, as a worst-case disturbance, is usually a sufficient model for a disturbed channel.

If the signal-to-noise ratio is large enough, digital modulation methods can be used, e.g. B. QAM or QPSK . This means that more than two states (more than 1 bit) can be coded per symbol . The transmission rate then results as the product of the symbol rate and the dual logarithm of the M states possible per symbol .

${\ displaystyle R = f_ {s} \ cdot \ log _ {2} (M) \ quad \ left \ lbrack {\ frac {\ text {bit}} {\ text {s}}} \ right \ rbrack}$

In the simplest variant, a digital signal takes on two states, which can be designated with "0" and "1". This is called binary . Three states are called ternary . With the same bit rate and three states for the signal parameter, the required bandwidth is only 63% of the bandwidth (see Nyquist bandwidth under Shannon-Hartley's law :) that is required for binary transmission. Four states are called quaternary  - with the same bit rate and four states per symbol, the required bandwidth is only 50%. ${\ displaystyle {\ tfrac {\ ln (2)} {\ ln (3)}} \ approx 0 {,} 63}$

In either case, the channel capacity represents the upper bound on the data rate; This means that it is not possible with any method to transmit more information per unit of time via a channel than is indicated by its capacity ( Shannon's source coding theorem ):

${\ displaystyle R \ leq C}$

Examples of data transfer rates

Wired

default Data transfer rate comment
DVB-C 4-5 Mbit / s MPEG-2 encoding for video
DVB-C HD 6-18 Mbit / s MPEG-4 AVC encoding for video
DVB-C2 5-8 Mbit / s MPEG-4 AVC encoding for video
FireWire 400 approx. 400 Mbit / s
Firewire 800 approx. 800 Mbit / s Another Firewire S3200 specification, downwardly compatible with previous standards, with the same 9-pin connector type as FW 800, achieves up to approx. 3.2 Gbit / s and is being further developed and used primarily for professional applications in the audio and TV sector
I²C 0.1 / 0.4 / 1.0 / 3.4 Mbit / s
NVMe 32 Gbit / s PCIe × 4, 128b130b encoded
Parallel ATA (IDE) up to 1064 Mbit / s 16 bit parallel
Parallel SCSI 40-2560 Mbit / s depending on the type , 8 or 16 bit parallel
SAS-1 ( Serial Attached SCSI ) 3 Gbit / s 8b10b encoded
SAS-3 12 Gbit / s 8b10b encoded
Serial ATA 1.5 Gbit / s 8b10b encoded
Serial ATA Revision 2.x 3 Gbit / s 8b10b encoded
Serial ATA revision 3.x 6 Gbit / s 8b10b encoded
External Serial ATA (eSATA) 3 Gbit / s 8b10b encoded
SATA Express 16 Gbit / s PCIe × 2, 128b130b encoded
Thunderbolt (interface) 10 Gbit / s also known as light peak
Thunderbolt 2 (interface) 20 Gbit / s
Thunderbolt 3 (interface) 40 Gbit / s
USB 1.0 / 1.1 1.5 / 12 Mbit / s
USB 2.0 480 Mbit / s only fully achieved for devices with the certification logo
USB 3.0 (USB 3.1 Gen 1; USB 3.2 Gen 1) 5 Gbit / s Gross rate with 8b10b coding
USB 3.1 Gen 2 (USB 3.2 Gen 2) 10 Gbit / s Gross rate with 128b132b encoding
USB 3.2 Gen 2x2 20 Gbit / s

Wireless

default Data transfer rate comment
DCF77 (radio clock signal) 1 bit / s
Mars probe Mariner 4 (1964) 8.3 bit / s
GSM (cellular) 9.6 kbit / s
IrDA 1.0 (infrared interface) 9.6-115 kbit / s
IrDA 1.1 4 Mbit / s
IrDA 1.3 16 Mbit / s
GPRS (cellular 2G) 53.6 kbit / s (theoretically up to 171.2 kbit / s)
Mercury probe Mariner 10 (1973) 100-150 kbit / s

BGAN (Internet via satellite) up to 420 kbit / s
DECT (wireless landline phones) approx. 800 kbit / s
UMTS (mobile radio 3G) 384 kbit / s
HSDPA (mobile data transmission 3.5G) 3.6 / 7.2 Mbit / s
Digital Radio Mondiale 11-26 kbit / s
DRM + 35-185 kbit / s
DMB 1-2 Mbit / s
Bluetooth 2.0 + EDR 3 Mbit / s
DVB-T 2-3 Mbit / s MPEG-2 encoding for video
DVB-S 4-5 Mbit / s MPEG-2 encoding for video
DVB-S2 5-20 Mbit / s MPEG-4 encoding for video
WiMAX 40-100 Mbit / s

LTE-Advanced (cellular 4G) 1000 Mbit / s
WLAN (wireless data transmission) 1-6933 Mbit / s in the popular IEEE 802.11g standard, typically 20 Mbit / s net and 56 Mbit / s gross
ZigBee 250 kbit / s

Display in the mobile phone display ː see cellular standard

Computer network

default Data transfer rate comment
Arcnet 2.5 Mbit / s, 20 Mbit / s Old technology.
Token ring 4 Mbit / s, 16 Mbit / s Old technology. Specifications for 100 Mbit / s and 1000 Mbit / s are available.
PowerLAN 14/85/200/500 / 1200/2000 Mbit / s
Fiber Channel 1 to 128 Gbit / s
single fiber optic cable 107 Gbit / s Record for a single conductor without frequency division over 160 km
InfiniBand 200 Gbit / s HDR with 4-channel connection
Ethernet 10 Mbit / s to 400 Gbit / s
Intercontinental fiber optic bundle 1 Tbit / s
laser 43 Tbit / s World record for the fastest data transfer with a laser

Internet

For internet access :

default Data transfer rate comment
modem maximum 56 kbit / s
ISDN 64 kbit / s, 128 kbit / s when using both B-channels

2 Mbit / s with primary rate connection

ADSL 384 kbit / s downstream and 64 kbit / s upstream (DSL "light") up to

25 Mbit / s downstream and 3.5 Mbit / s upstream ( ADSL2 + )

VDSL 25 Mbit / s to 300 Mbit / s
DOCSIS (TV cable) 10 Gbit / s downstream and 1 Gbit / s upstream
Fiber to the Home (FTTH; glass fiber) 1+ Gbit / s downstream

Video and audio signals

default Data transfer rate comment
Telephone quality conversation 64 kbit / s about 3.1 kHz bandwidth (ISDN - practically no irrelevance  and redundancy reduction ("compression") techniques are used.)
Compressed music file usually between about 24 kbit / s ( streaming audio via analog telephone modem ) and

9.8 Mbit / s (maximum data rate for losslessly compressed multi-channel audio tracks of an SACD / DVD-A )

Lossless compressed music file between 320 kbit / s and 5000 kbit / s depending on the source Flac
Audio CD approx. 1411 kbit / s, sampling rate 44.1 kHz, 16 bit and two channels practically without irrelevance and redundancy reduction
SD television picture approx. 3 Mbit / s MPEG-2 compressed
Video DVD approx. 6 Mbit / s MPEG-2 compressed
SD video approx. 400 Mbit / s 576p 50 Hz uncompressed
HD video approx. 1.3 Gbit / s 720p 60 Hz 24b / px uncompressed
Full HD video approx. 3 Gbit / s 1080p 60 Hz 24b / px uncompressed
4K UHD1 video (2160p) approx. 10.2 Gbit / s at 30 Hz

approx. 14.93 Gbit / s at 60 Hz

2160p
8K UHD2 video approx. 24 Gbit / s 4320p 120 Hz

The higher data transmission rates of newer technologies increasingly enable the transmission of increasingly broadband audio and video signals.