Bandwidth calculation method and description of Big B and Small B

 

1. Description of byte and bit

In computer science, bit is the smallest unit of information, which is called a binary bit. It is usually represented by 0 and 1. Byte is called a byte. It consists of eight (8 bit) bytes (1 byte), used to represent a character in the computer. Bit and byte can be converted. The conversion relationship is 1 byte = 8bit (or 1B = 8b, that is, 1bit is abbreviated to 1B (note that it is a lowercase English letter B), and 1byte is abbreviated to 1B (note that it is a capital English letter B ).

 

In a computer network or a network operator (Internet Service ProviderIn general, the unit of bandwidth rate is expressed in BPS (or B/S, Small B); BPS indicates the number of bits per second (that is, the number of bits transmitted per second, it is the abbreviation of bit per second. In practice, 1 mbps bandwidth means 1 Mbps (1 Mbps for megabits per second instead of 1 Mbps for megabytes ).

 

Conversion formula:

1 byte = 8bit
1B = 8B ---------- 1B/S = 8B/s (or 1bps = 8bps)
1kb = 1024b ---------- 1kb/S = 1024b/s
1 MB = 1024kb ---------- 1 Mb/s = 1024kb/s

 

Standard tip: in actual writing specifications, B should represent byte (bytes), and B should represent bit (BIT ), however, in actual writing, bit and byte are both mixed into B, for example, both MB/s and MB/s are mixed into MB/s, this leads to errors due to unit confusion in actual computing.

 

Ii. Actual use

In actual online applications, when downloading software, you often see the words "Bandwidth speed", such as KB (kb/s) and 103kb/s, because the ISP's line bandwidth is measured in BITs (bit, that is, Small B), and the download software usually displays bytes (byte, 1 byte = 8 bits ), therefore, the actual value can be obtained through conversion.

 

However, we can convert it according to the conversion formula:

128kb/S = 128 × 8 (kb/s) = 1024kb/S = 1 MB/S: 128kb/S = 1 MB/S

That is, we need to have 1 Mbps of bandwidth and the download speed can reach kb/s.

 

Theoretically: the theoretical bandwidth speed of 2 m (2 Mb/s) is 256kb/s (that is, 2048kb/s), and the actual rate is about 80 -- 200kb/s; (This is caused by many factors, such as the user's computer performance, network equipment quality, resource usage, network peak periods, website service capabilities, line attenuation, and signal attenuation ).

The theoretical bandwidth of 4 m (4 Mb/s) is 200 kb/s, and the actual rate is about --- kb/s.

 

Iii. Description of ADSL bandwidth

Asypolicric Digital Subscriber Loop Technology is an asymmetric digital user line technology to achieve broadband access to the Internet. As a transmission layer technology, ADSL makes full use of existing copper wire resources, A pair of twisted pair wires provide 8 Mbps downstream bandwidth of 640 Kbps (theoretically 1 Mbps), thus overcoming the "bottleneck" of traditional users in the "Last Mile ", it realizes broadband access in the true sense.

 

Uplink speed: indicates the data transmission rate when the user's computer sends information to the network.

Downlink rate: the transmission rate at which the network sends information to the user's computer. For example, if you use ftp to upload files to the Internet, the upload speed will be "Uplink speed". If you download files from the Internet, the download speed will be "downlink speed ".

Of course, in the actual upload and download process, the quality of lines, devices (including computers and other devices) will also have a greater or less impact on the speed.

 

 

Impact of uplink speed on downlink speed:

TCP/IP stipulates that each packet requires a backend of acknowledge information. That is to say, a reply to the received information is required for the transmitted data to determine the transmission speed, and decide whether to re-transmit the lost data.

Part of the upstream bandwidth is used to transmit the Acknowledge data. When the upstream load is too high, the transmission speed of acknowledge data will be affected, and the download speed will be affected. This has a particularly significant impact on Asymmetric Digital loops, that is, connections with upstream bandwidth much less than the download bandwidth.

Some experiments have proved that when the upload is full, the download speed is about 40% of the ideal speed, which can explain why many friends get a higher download speed when using BT to download.

 

Summary:

In the bandwidth unit provided by the network operator, "BPS" refers to "bit per second ". The actual speed refers to the BPS "Byte persecond" (1 byte = 8bit ).

In the calculation of the uplink or downlink speed of the network speed, the value must be divided by 8 to convert the bit to byte.

For example, the lower speed (that is, the download speed) is 1 Mb/s, and the equivalent value is 128 Kbps. The conversion method is 1 Mbps = 1024/8 (Kbps) = 128 kbps is Kbyte/s.

 

 

 

 

 

 

Organized from Network

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