In the field of communication transmission, some proper terms are often heard, such as: baud rate, bit rate, etc. Most people may not understand its meaning. What is baud rate? This article will explain the baud rate and other related knowledge in detail.  Show 1. What is bit rate Bit rate is also known as signaling rate and information transmission rate (referred to as information rate, information rate). Its definition is: the amount of information transmitted per unit time (per second) of the communication line (or system), that is, the number of binary digits that can be transmitted per second, usually expressed in Rb, and its unit is bits per second (bit/s or b/ s, the English abbreviation is bps). In a binary system, the information rate (bit rate) is equal to the signal rate (baud rate), for example, when the system transmits at 50 binary symbols per second, the information rate is 50bit/s, and the signal rate is also 50Bd (baud rate). ). In the case of no modulation, the bit rate is equal to the baud rate; with phase modulation technology, the bit rate is not equal to the baud rate. The sending device and the receiving device of the communication system must work under the same baud rate, otherwise there will be frame synchronization errors. 2. What is the baud rate Baud rate is also known as code transmission rate, symbol transmission rate (referred to as symbol rate), signal transmission rate (referred to as signaling rate) or modulation rate. Its definition is: the number of symbols (pulses) transmitted per unit time (per second) of the communication line (or system); or the number of transformations of the modulated signal waveform per unit time during the signal modulation process, usually expressed in RB, the unit is baud (Bd or Baud, the former specification). If 1 symbol is transmitted per second, it is called 1Bd; if the time length of 1 symbol is 200ms, then 5 symbols can be transmitted per second, then the symbol rate (baud rate) is 5Bd. The baud rate (symbol rate) does not limit what kind of code unit it is, so the system of this code unit must be specified when the baud rate is given. For M-ary symbols, the relationship between bit rate (information rate) Rb and baud rate (symbol rate) RB is: Rb=RB·lbM In the formula: lbM=log2M, which represents the logarithm of M with the base 2. Obviously, for binary symbols, since lb2=1, Rb=RB, that is, the baud rate and the bit rate are numerically equal, but the units are different, that is, the meanings of the two are different. For example, if the baud rate is 600Bd, then in binary, the bit rate is also 600bit/s; in quaternary, since lb4=2, the bit rate is 1200bit/s. It can be seen that multiple bits can be transmitted in one symbol. 3. Data transfer rate Data transfer rate is also known as data transfer rate and data transfer rate. Its definition is: the number of characters transmitted per unit time (per second) of the communication line (or system); or the number of code groups (blocks) or the number of bits transmitted per unit time (per second). Its unit is character/second; or code group/second, bit/second (it can be seen that when the data transmission rate uses "bit/s" as the unit, it is equal to the bit rate). For example, in a computer asynchronous serial communication system, the data transmission rate is 960 characters/s, and each character includes 1 start bit, 8 data bits, and 1 stop bit, then the corresponding bit rate is 10×960 Bit/s=9600bit/s=9600bit/s; because it is binary encoding, the corresponding baud rate is also 9600Bd. 4. The connection between baud rate and bit rate: baud, bits and symbols Baud (Bd) is a unit of measurement used to measure the number of signal changes per second for devices such as modems, that is, the number of times the state of the communication line changes per second, not the amount of data transmitted. The word "Potter" comes from a French name - Baudot. He developed a coding scheme for the French telegraph system in 1877. If the modem transmits 1 bit (bit) of data every time the signal changes, then the bit rate (information rate) of the system is the same as the baud rate (symbol rate). However, after the coding technology is adopted, 1Bd (1 signal change) can be expressed as 2bit or more bits (bits). Each baud represents 2bit (bit) is called double-bit encoding, and each baud represents 3bit (bit) is called three-bit encoding. That is to say, one voltage (or current) waveform change may include several bits of data, therefore, baud rate and bit rate cannot be confused; the former refers to the number of voltage (or current) changes (changes), and the latter refers to The amount of data transferred. A code cell is a digital unit that carries information, and refers to a waveform symbol that transmits a digital signal in a digital channel, that is, "a signal coding unit on the time axis". Symbols may be binary or multi-binary. A bit is the measurement unit of "information amount", and the amount of information carried by one binary number is 1 bit (bit). For example, 10010110 is an 8-bit binary number, and the amount of information carried is 8 bits. 5. The difference between baud rate, bit rate and communication speed There are many transmission-related proper terms in the field of communication, many of which are not particularly understood by laymen. 5.1 Concept Bit rate: Refers to the number of bits (bits) transmitted per second. The unit is bps (Bit Per Second). The higher the bit rate, the more data is transmitted per second. Baud rate: Indicates the number of symbols transmitted per second, which is an indicator to measure the data transmission rate. In the information transmission channel, the signal unit that carries the data information is called the symbol, and the number of symbols transmitted through the channel per second is called the symbol transmission rate, or baud rate for short. The baud rate is an indicator of the bandwidth of the transmission channel. Transmission rate: Transmission rate is a general term that refers to the rate at which data is transmitted from one point to another. Contains the above bit rate, baud rate, etc. Communication speed: Communication speed and transmission speed are also a general term. For example, the I2C communication speed is 100KHz, and the SPI maximum communication speed supports 150Mbps. 5.2 Difference between bit rate and baud rate 5.2.1 Bit rate Bit (bit) I believe everyone knows that 1 byte (Byte) is equal to 8 bits (bit). Naturally, bit rate is the number of bits transmitted per second. 5.2.2 Baud rate In the field of electronic communication, Baud is the modulation rate, which refers to the rate at which the effective data signal modulates the carrier, that is, the number of times the modulation state of the carrier changes per unit time. It is a measure of the symbol transmission rate, 1 baud refers to the transmission of 1 symbol per second, and through different modulation methods, multiple bits of information can be loaded on one symbol symbol. Similar to bit rate, you only need to understand the "baud" (ie symbol symbol) in baud rate as a transmission unit. 5.2.3 Relationship between baud rate and bit rate Bit rate = baud rate x number of bits corresponding to a single modulation state. 1 Baud = log2M (bit/s) where M is the number of coding levels of the signal. Can also be written as: Rbit = Rbaud log2M (Rbit: bit rate; Rbaud: baud rate) It can be concluded that the bit rate of two-phase modulation (a single modulation state corresponds to 1 binary bit) is equal to the baud rate; the bit rate of four-phase modulation (a single modulation state corresponds to 2 binary bits) is twice the baud rate; eight The bit rate for phase modulation (3 binary bits for a single modulation state) is three times the baud rate; and so on.
I have to admit, I haven’t thought about baud rate in quite some time. In my daily work I have moved ‘up the stack,’ and can safely assume that someone else has done the work to ensure that the information I send between software components gets to its destination as intended. It’s good, however, to understand how this reliability comes about, and a basic understanding of the role baud rate and bit rate helps. The Challenge of Streaming 1s and 0s from Point A to Point BIt turns out that getting a signal from one end of a piece of wire or fiber to the other is pretty tricky, especially with increasing line length and transmission rate. The important thing to know is that the signal that comes of the line is not exactly the same as the signal that went in. See the figure below: Figure 1: Transmission Line Characteristics From the figure we can see that the cooper cable of the transmission line is a lot more complex than a straight connection. The length of the cable adds resistance, induction, and capacitance components which distort the signal as it travels. In the case of optical fibre, the multiple paths photons can travel (even with single mode fibre) have different lengths, stretching and distorting the signal. The output signal shown is smaller and less defined than the source signal and it is delayed with respect to the timing grid. The big advantage that optical technologies have over copper technologies, apart from lower loss for a given length, is less electromagnetic interference. Any single electrical signal flowing down a wire will emit some of the signal as electromagnetic energy, which can be picked up by other conductors (wires) and converted back into an electrical signal. This means that foreign signals may also be present on the transmission line, as well as the original signal. A key requirement is to be able to ensure the required signal can be distinguished from the unwanted signals (also known as “noise”) at the receiving end. The “Symbolic” Nature of Data on the WireThe challenge with data transmission is to get a signal from point A to point B, carrying as much information as possible, in a reliable manner. Note that the 1s and 0s we send as application developers may have different representations while they are in transit or ‘on the wire.’ For that reason when talking about baud rate we talk about symbols and not bits. Symbol rate is effectively the baud rate. I’ll explain the conversion from bit rate below, but with that in mind, the encoding process needs provide the following functions:
Baud RateBaud rate, then, is the measure of the number of changes to the signal (per second) that propagate through a transmission medium. The baud rate may be higher or lower than the bit rate, which is the number of bits per second that the user can push through the transmission system. Bits will be converted into baud for transmission at the sender side and the reverse conversion will happen at the receiver end so that the user receives the bit stream that was sent. A few simple definitions before we move ahead:
So to convert bit rate to baud rate you multiple baud rate by the number of bits per symbol by the number of channels being used: Bit rate = baud rate * bits per symbol * Channels Next I’ll explain how baud rate and bit rate apply to Solace appliances. Connecting to Solace PubSub+ Event Broker AppliancesAll Solace PubSub+ Event Broker appliances use ethernet connections for data and management connections, and provides an RS232 serial port so you can configure things before an IP address is assigned. I will start by explaining the simpler RS232 and move on to 1GE ethernet. RS232 (Serial Console)Serial communication via a terminal server to the Solace 3xx0 Console, via RS232, is one place where you will find baud rate mentioned within the Solace documentation. RS232 is one of the oldest and simplest computer communication methods. It is pretty slow, with speeds measured in kilobits per second rather than megabits or gigabits, and it is used for initial configuration of Solace hardware, an action that is typically carried out just once upon installation. The entire RS232 standard is not required for a console connection, so I’ll stick to the relevant parts. The RS232 specification is applicable to copper transmission only and does not require any specific ‘standard’ of copper cabling. It is an asynchronous, serial communications protocol that transmits individual ‘data words’ between computer systems. While a data word is configurable between 5 and 8 bits, the usual settings are to transfer 8 bits – or a single byte – as the data word. The specification outlines the signal formats and signal levels as well as the interface specifications (connector types, pin assignments, etc.). The protocol is pretty rudimentary by modern standards as the binary 1s and 0s are transmitted on the wire without any real encoding other than specifying the voltage levels for a 0 and a 1. The specification has information that is transmitted byte by byte – each byte delineated by a start bit and stop bit – and the standard allows for an optional parity bit for detection of bit errors. In its simplest form, bi-directional RS232 communication needs two signal wires and a ground reference. This is shown, between two computers, in the following figure. Figure 2: RS232 DTE-DTE Connection The signal transmitted is shown in the next figure, where a ‘space’ or a ‘0’ being sent as a positive voltage between +5 volts and +15 volts and a ‘mark’ or a ‘1’ as a negative voltage between -5 volts and -15 volts. Figure 3: RS232 Line Levels A byte of information is signaled by enclosing the byte with start and stop bits and declaring the idle state of the signal line. This means that clock signals do not need to be propagated end-end and that, as long as the baud-rate is agreed between the sender and the receiver, the receiver can start its ‘clock’ on receipt of a start bit. The RS232 standard also allows a very primitive form of error checking in the form of a parity bit. This can be used to indicate that an error has occurred in the data word that contains the parity bit. The parity bit can be set to maintain an even or an odd set of 1s in the data word. For example, if set to even parity and the data word contains 3 x 1s then the parity bit will be set to 1 to maintain the even number desired. If even parity is assigned and a data word is received with an odd number of bits and is set to 1, then there is an error. The parity check does not detect all errors though, like in the example where ‘bit 4’ moved from 0 to 1 and bit 7 moved from 1 to 0. In this case, it is optional and often not used. The Solace console has the basic RS232 configuration:
On the wire, a transmitted byte will appear as shown (for ASCII ‘A’): Figure 4: RS232 ‘Framing’ From the trace, you can see that the line in its idle state is held at the negative state, or ‘mark’. The receiving clock will not run until the line transitions to a positive state, or space, and it will then run at the agreed rate so that it can sample the signal at the correct points. The stop bit is a single bit width ‘mark’. This type of coding means that even if I send a set of repeating bytes with all 0s or all 1s, the receiver will still see a ‘clock start’ for every byte, so can keep time with the sender. The usable baud rate setting of the RS232 connection is drastically affected by the length of the cable that is used between the Solace appliance and the data centre terminal server. The higher the baud rate that is configured, the shorter the cable length. The default 115,200 baud setting is designed for very short cable length to a ‘top of the rack’ terminal server found in newer data centres. For data centres where larger terminal servers are deployed that serve a whole suite of racks, the default should be changed to allow longer cables and reliable communication. The value of 9,600 is a common terminal server speed for this style of terminal server/console deployment. To change the baud rate of the serial console, you can issue the following commands in ‘enabled’ mode: solace# configure It should be obvious, but both ends of the RS232 connection must have the same configuration. Gigabit (1000BaseT) EthernetI’m going to talk about 1 gigabit ethernet (GE) since most 10 GE connections are over fibre these days. Gigabit ethernet is used for the management connections to the Solace 3×00. A detailed description of the entire GE data path is beyond the scope of this article, and there are no configuration tweaks available, but enough will be covered so that an appreciation of bits and ‘bauds’ (or symbols) can be reached. The standard allows 1 gigabits per second of data transfer using CAT 5 copper cables installed in most data centres and buildings. It is pretty much the ‘connect and it works’ system for large scale communication in most environments today. While your PC might connect over Wi-Fi at 50 Mbps, 100 Mbps, or perhaps 200Mbps (using 802.11ac Wi-Fi), the backhaul connection to the access point is likely to be gigabit ethernet. So, given that in the previous section we said that RS232 could only sustain 115.5 kilobits per second over quite short distances, how does gigabit ethernet allow buildings to be wired up? The first clue is in the cable. By defining the standards for the cable to, ethernet designers have a known and proven transmission system. CAT 5 was chosen because it was already everywhere in data centres and buildings because it was specified for the previous 100Mbps ethernet standard. The cable itself is designed to work at up to 125Mbps which is required for 100Mb ethernet. Reusing the existing infrastructure would help to significantly reduce the cost of the upgrade from 100Mbps to 1Gbps and increase adoption. The challenge for the 1GE designers was how to get 10x the information through the same copper infrastructure with similar reliability and useable communication distances. 100mbps ethernet uses what is called 4B/5B communication and adds bits to the data flow for error detection and correction. It also uses a separate pair of wires for transmit and receive which is similar to the previous RS232 communication between DTEs. Figure 5: !00Base-T Uses Separate TX / RX Pairs for Full Duplex Transmission. To reuse the cabling, the 1GE designers used a few optimizations to make 10x the data volume fit into the same transmission capacity:
Figure 6: 1000Base-T Uses All Four Pairs with Hybrid Circuits to Allow Full Duplex Transmission Skipping a large amount of detail on bitstream scrambling, convolutional/trellis encoding and Viterbi decoding, the standard then uses a PAM5 modulation scheme to transmit data 2 bits per symbol. This reduces the rate to 250M/2 = 125M baud (symbols) per second which is within the capacity of the environment. Figure 7: Gigabit Ethernet 4D-PAM5 Line Levels to Support Two Bits Per Symbol + Control. The PAM5 scheme is used instead of PAM4 – only 4 signal levels are needed to represent all combinations of two bits – in order to allow extra symbols for signaling and control. The use of convolutional coding and Viterbi decoding provides error correction for the transmission path. This makes up for the reduced voltage difference between ‘states’ (0.5 volt rather than 1 volt used for 100Mbps ethernet) that would drive down the signal-to-noise ratio and add to the errors experienced. Unlike the RS232 example above, this is error correction and it can cope with multiple bit errors. The error correction effectively adds about 6dB to the signal-to-noise ratio allowing gigabit ethernet to run similar distances on CAT5 as 100Mbps ethernet. SummaryBaud rate is the measure of the number of changes to the signal (per second) that propagate through a transmission medium. The baud rate may be higher or lower than the bit rate, which is the number of bits per second that the user can push through the transmission system. Bits will be converted into baud for transmission at the sender side and the reverse conversion will happen at the receiver end so that the user receives the bit stream that was sent. A few simple definitions: Bit rate – the number of binary ‘bits’, 1s or 0s to be transmitted per second To Convert: Bit rate = baud rate * bits per symbol * Channels Visit the solace documentation page to learn more about configuring the baud rate for a PubSub+ Event Broker appliance. |
Is the number of bits transmitted per second is unit of modulation rate or the rate of symbol transmission?
zusammenhängende Posts
Urheberrechte © © 2024 frojeostern Inc.
