What is the relationship between MHz and Mbps?

Mbps is the unit of data traffic, and MHz is the unit of frequency.

Hz (Hertz) refers to the bandwidth of the cable (BandWidth). Represents the number of oscillations of the electrical signal in the line per unit time, such as the frequency bandwidth of the Category 5 twisted pair is 100MHz. This value is fixed, and the Dongjiang iodine stalks fly when the winter river is said to have a medium. MHzj is Mega Hertz (MHz) is one of the fluctuation frequency units. Bps generally refers to the data rate (also known as the data rate), which measures the number of bits transmitted by the line per unit time. Mbps is the abbreviation of Million bits per second. 1 Mbps represents 1,048,576 bits per second (1Mb=1024Kb=1024*1024bit), that is, 1,048,576 / 8 = 131,072 bytes = 128 KB = 0.125MB per second. Mbps is the unit of rate, megabits per second

Concept analysis

With the popularity of the network and the increasing use of integrated wiring, the transmission level is getting higher and higher, from Category 3 to Category 4 to Category 5, and six types of wiring products have been put on the market. The main parameter defining the level of the descriptor is the transmission bandwidth (MHZ).

At the same time, web applications are also emerging. Transmission media from 10Base5 (thick cable), 10Base2 (thin cable), 10BaseT (twisted pair), 10BaseFL (fiber) to 100BaseTX (STP/UTP), 100BaseT4 (4/5 class UTP), 100BaseFX (fiber), to the present Gigabit fast network has emerged. The main parameter used to describe these applications is the rate (Mbps).

In fact, the Shennong formula has long outlined the relationship between bandwidth B and rate C:

C=B*Log(1+SNR)

Where B is the channel bandwidth, the so-called bandwidth refers to the frequency range in which the signal can be transmitted with appropriate fidelity, and its unit is Hz, which is state-owned by the channel itself, and has nothing to do with the contained signal. SNR is the signal-to-noise ratio, which is determined by the system's transmitting and receiving equipment and the electromagnetic environment in which the transmission system is located. The rate C is a calculation result, which is determined by the combination of B and SNR, and its unit is bps, which is conceptually characterized as a binary digit transmitted per second.

It can be seen that given a channel, the bandwidth B is also given, and the signal-to-noise ratio SNR can be changed to obtain a different transmission rate C. There is a one-to-many relationship between MHz and Mbps, that is, the same bandwidth can transmit different bit stream rates. At the same time, Mbps is application-dependent; MHz is application-independent.

Technical discussion

If you want to give an image of the image, then the car speed and engine speed are just right. When the rotational speed is given, the speed of the car can be calculated with the gears known. In this analogy, the gears act as a bridge. In fact, gears are like cars and engines like speed and bandwidth for coding systems.

Encoding is used for information transfer by a computer. By coding the information, many technical problems, such as synchronization, bandwidth limitations, etc. can be solved. Encoding is critical to the reliable transmission of information.

There are currently two basic coding series. The first is to add a sync bit per N bits to make synchronization possible (such as Manchester encoding when N = 1; 4B5B encoding when N = 4), but this requires a larger bandwidth than the original . And the more sync bits, the greater the bandwidth needs. In order to reduce the bandwidth, it is possible to use an encoding system that adds one sync bit (ie, 7B8B encoding) every 7 bits, but then, when a longer stream of the same type of bit stream is transmitted, the synchronization becomes Very difficult.

Another type of coding is to reduce the bandwidth by increasing the number of levels. The more the number of levels, the less bandwidth is needed. However, when transmitting a long string of continuous signals obtained by 0 encoding, synchronization becomes almost impossible. For example, when we use 5 levels, we need 4 comparators, and each comparator should have its proper tolerance range. That is to say, when we choose the total number of levels, we should also take into account the signal-to-noise ratio (SNR) to be able to identify these different levels.

Manchester, NRZ1 and MLT-3 encoding are the three encoding systems currently used. Their transmission factors are 1, 0.5 and 0.25, respectively. These transition factors can be defined as the ratio of MHz pairs. Table 1 lists the summary features of several coding systems in terms of synchronization and bandwidth.

From this point of view, any coding system has its technical limitations. In addition, there are some parameters such as DC components that also impose certain restrictions on the encoding. In practical applications, the current major coding systems are used together to make a compromise between bandwidth and synchronization, or a bias, for example, a pair. Applications with higher synchronization requirements can choose the Manchester encoding system or other encoding methods that can generate timing. For example, a 100 Mbps application using MLT-3 encoding requires 25 MHz bandwidth; when 4B5B encoding is used in combination, the system needs to add an additional 25 Mbps overhead, and the entire system needs 31.25 MHz bandwidth. The advantage is that the system is Synchronization has become easier. In addition, it is worth mentioning that 100 Fast Ethernet uses the 5B6B encoding system (IEEE802.13), which can be said to be a typical example of bandwidth and synchronization tradeoffs. Table 2 lists the current partial applications and the coding systems they use.

in conclusion

As a user, the most interesting is the communication rate. The rate is a description of the communication from the application level. In order to increase the communication rate, there are two ways to consider: one is to improve the transmission performance of the cable system, thereby determining the bandwidth; the other is to select the appropriate coding system, which determines the conversion factor.

Wiring manufacturers have already developed Category 5 cable systems capable of supporting more than 100 MHz. And they continue to invest in research and development of higher performance cable systems. International organizations such as EIAAA/TIA, ISO/IEC have developed standards for defining LAN component levels through bandwidth.

Although the bandwidth is physically limited, a higher communication rate can be obtained by a suitable encoding system. In particular, the coding system is application-dependent. This means that a new application with the same bit rate but different coding methods may not be supported by the original system, so at the time of design, if only Considering those wiring components that support existing applications and choosing a bit stream rate of MHz to describe, this will lead to serious erroneous decisions. From this perspective, any open system should be independent of the application. And only by using MHz to describe the communication rate, we can make a full choice from the current and future wide application areas. For performance grading problems with integrated wiring systems, we can only measure with bandwidth and not with rate.