Bandwidth and data transfer rate

Three, in-memory bandwidth
Vi. Bandwidth in the communication
In the field of communication and networking, the meaning of bandwidth is also different from the above definition, which refers to the use of network signals
The difference between the highest frequency and the lowest frequency, or the "width of the band", the so-called "Bandwidth",
"Channel Bandwidth"-This is also the most rigorous technical definition.
In a copper-medium cabling system such as 100M Ethernet, the channel bandwidth of a twisted pair is usually measured in MHz,
It refers to the signal-to-noise ratio in the case of a constant allowable channel frequency range, however, the channel bandwidth of the network with its data
The transmission Capacity (unit byte/s) has a stable basic relationship. We can also use highways to make metaphors:
On a high-speed road, the maximum amount of traffic it can withstand is equivalent to the network's ability to transport data, and this highway
The width allowed to form is equivalent to the bandwidth of the network. Obviously, the higher the bandwidth, the more resources you can use to transfer data,
Thus, the higher the speed can be achieved, in addition to this, we can improve the signal quality and eliminate the bottleneck effect.
Higher transmission speeds.
The proportional relationship between network bandwidth and data transmission capability was first made by Bell Labs engineer Claude.
Shannon found, so this law is also known as Shannon law. On the popular side, the number of networks
The "network bandwidth" is exactly the same as the "network bandwidth", and the "bus bandwidth" on the surface
Form a conceptual unity, but the two are essentially not a meaning, far from the difference.

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Definition of data transfer rate
Data transmission rate is one of the important technical indexes of data transmission system. The data transfer rate is equal to the number of bits per second (bit/second) of the binary bits in bytes/sec (b/s), recorded as BPS. For binary data, the data transfer rate is:

s=1/t (bps)

where T is the time required to send each bit. For example, if the time required to send a bit 0, 1 signal on the communication channel is 0.001ms, then the data transfer rate for the channel is 1 000bps.

In practical applications, the usual data rates are in Kbps, Mbps, and Gbps. which

1kbps=10^3bps 1mbps=10^6kbps 1gbps=10^9bps

Bandwidth and data transfer rate
In modern network technology, people always use "bandwidth" to express the channel data transmission rate, "bandwidth" and "rate" are almost synonymous. The relationship between channel bandwidth and data transfer rate can be described by the Nyquist (Nyquist) Rule and Shannon (Shanon) Law.

The Nyquist criterion states that if the interval is π/ω (ω=2πf), the narrow pulse signal is transmitted through the ideal communication channel, then there is no mutual harassed between the front and rear code elements. Therefore, the relationship between the maximum data transfer rate for binary data signals Rmax and the communication channel bandwidth B (b=f, unit Hz) can be written as:

RMAX=2.F (bps)

For binary data if the channel bandwidth b=f=3000hz, the maximum data transfer rate is 6000bps.

The Nyquist theorem describes the relationship between the maximum data transfer rate and channel bandwidth of a finite bandwidth, noiseless channel. Shannon's theorem describes the relationship between the maximum transmission rate of a finite bandwidth, a random thermal noise channel, and the channel bandwidth and signal-to-noise ratio.

Shannon theorem points out: When the data signal is transmitted on a channel with random thermal noise, the relationship between data transmission rate Rmax and channel bandwidth B and Snr is:

RMAX=B.LOG2 (1+s/n)

, the Rmax unit is BPS, the bandwidth B is Hz, and the signal-to-noise ratio s/n is usually expressed in db (decibels). If S/n=30 (DB), then the signal-to-noise ratio is based on the formula:

S/n (DB) =10.LG (S/n)

You can have it, s/n=1000. If bandwidth b=3000hz, then rmax≈30kbps. Shannon's law gives a limit value of the maximum data transfer rate for a limited bandwidth, thermal noise channel. It means that for a communication channel with a bandwidth of only 3000Hz, the signal-to-noise ratio at 30db does not transmit data at a rate over 0kbps, regardless of whether the data is represented by binary or more discrete level values.

Therefore, the communication channel maximum transmission rate and channel bandwidth have a clear relationship, so people can use "bandwidth" to replace the "rate." For example, people often use the network's "high data rate" to express the "high bandwidth" of the network. So "bandwidth" and "rate" are almost synonymous in the discussion of network technology.
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bit rate. Baud rate

The following explanatory text comes from the web material:
① baud rate refers to the number of times the signal changes per second. Bit rate refers to the number of bits that can be transmitted per second. In the absence of modulation, the baud rate is exactly equal to the bit rate. The baud rate is not equal to the bit rate when using phase modulation technology.
The rate at which digital signals are transmitted by the ② digital channel is called data transfer rate or bit rate.
③ transmission rate refers to the number of bits per second transmitted, the transmission rate is often called baud rate.
④ baud rate refers to the number of times the line status has changed. Only each signal is equal to the number of bits per second when it conforms to one of the transmitted data.
The ⑤ baud rate is the rate of analog line signals, also called the modulation rate, measured by the number of oscillations per second of the waveform. If the data is not compressed, the baud rate equals the number of bits transmitted per second, and if the data is compressed, the number of data bits transmitted per second is usually greater than the modulation rate, making the exchange use baud and bits per second occasionally producing errors.
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The following text is from Wikipedia:
    in the field of electronic communication, the baud rate is the modulation rate, which refers to the number of baud in the unit time after the signal is modulated, that is, the number of changes in the carrier parameters in the unit time. It is a measure of the symbol transfer rate, usually in "baud per second" (bd/s), 1 baud per second refers to the transmission of 1 symbols per second. The
    baud rate is sometimes confused with bit rate, which is actually a measure of the rate of information transfer (messaging rate). The baud rate can be understood as the number of transmission code element symbols per unit of time (rate of transfer of symbols), through different modulation methods can load multiple bits of information on a code element. So the information transfer rate, bit rate, has such a relationship with the baud rate:
                             I = s log2n                 (Ⅰ)
where I is the messenger rate, S is the baud rate, n is the amount of information for each symbolic payload, in bits. So only if each symbol represents only one bit of information, such as baseband binary signals, the baud rate and bit rate are numerically equal, but they are not of the same meaning.
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    in the area of telecommunications and computing, bit rate , variable rbit) is the number of bits transmitted or processed within a unit of time. Bit rate is often used in telecommunications as a synonym for connection speed, transmission speed, channel capacity, maximum throughput, and digital bandwidth capacity. Bit rates are specified using "bits per second" (bit/s or bps) and are often associated with the SI prefix, such as "thousand" (kbit/s or Kbps), "Mega" (Mbit/s or Mbps), "Kat" (gbit/s or Gbps), and "Too" (tbit/ s or tbps).

Similar explanations endless, but what is the difference between baud rate and bit rate?

Personal comparisons tend to be explained by wiki, but there is still a doubt that the baud rate is a measure of the rate at which the data is transmitted. There is really a difference between the symbol and the message when the Transfer object is different.

Personally, in the field of communication and computing, a binary transmission signal is used, even if the symbol is converted into binary information (for example, the characters are described in ASCII code). So, what if we are using a three-way transmission signal (for example, high, 0, low-level three states). So at this time the transmission of the same amount of information at the bit rate is not used when the binary 1.5 times times. If we use octal or hexadecimal to transmit the signal. In fact, from the above formula Ⅰ can be seen, bit rate (messaging rate) and baud rate between the difference between a real coefficient log2n, which is a dimensionless amount, that is, a modulation method with the use of the relevant amount. So, in this sense, the bitrate is just a special case of the baud rate when using binary.

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In the field of electronic communication, the baud rate is the modulation rate, which refers to the number of baud in the unit time after the signal is modulated, that is, the number of changes in the carrier parameters within a unit time. It is a measure of the signal transmission rate, usually in "baud per second" (BPS).
The baud rate is sometimes confused with the bit rate, which is actually a measure of the rate of information transmission (messaging rate). The baud rate can be understood as the number of transmission code element symbols per unit of time (rate of transfer of symbols), through different modulation methods can load multiple bits of information on a code element.

Rigorous definition:
. Bit Rate
In the digital channel, the bitrate is the transmission rate of the digital signal, which is represented by the number of significant bits (bit) of the binary Code transmitted within a unit of time, expressed in bits per second bit/s (bps), kilobits per second (Kbps), or megabits per second (Mbps) ( Here K and M are 1000 and 1000000 respectively, instead of 1024 and 1048576 when the computer memory capacity is involved.

. Baud Rate
Baud rate index according to the signal to the carrier modulation rate, it is in the unit time the carrier modulation state changes the number of times to express, its unit is Porter (Baud). The baud rate is related to the bit rate: bit rate = baud rate x the number of bits corresponding to the individual modulation state.

How to differentiate between the two.
Obviously, the bit rate of the two-phase modulation (a single modulation state corresponds to 1 bits) is equal to the baud rate, the bit rate of the four-phase modulation (2 bits for a single modulation state) is twice times the baud rate, and the bit rate of the eight-phase modulation (3 bits for a single modulation state) is three times times the baud rate;

Reprinted from: http://blog.chinaunix.net/uid-346158-id-2130835.html