Detailed description and conversion method of bit, byte, BPS, BPS, PPS and Gbps in the network

Time:2020-6-27

bit
The smallest unit of computer memory. In a binary computer system, each bit can represent a digital signal of 0 or 1.

Byte
Byte unit, generally refers to the unit of storage medium size. A B (uppercase B is commonly used to represent byte) can represent a character (A-Z), a number (0-9), or a symbol (,.?!% & + – * /), but Chinese characters need 2 bytes.
1 Byte = 8    bits
1 KB   = 1024 Bytes
1 MB   = 1024 KB
1 GB   = 1024 MB
Note: when calculating the size of storage media, you need to convert it to the nth power of 2 (1KB = 2 ^ 10 bytes).

bps
Bits per second” is often used to indicate the transmission rate of data machine and network communication. For example, gigabitethernet port:
5 minute input rate 38410000 bits/sec, 6344 packets/sec
382410000 bits/sec = 382.41Mbps
So it is often said that fast Ethernet can achieve 100m transmission. In fact, the actual transmission file size is only 10MB = 100MB
Note: when calculating the transmission rate, directly use 1000 to convert (1 MB = 1000 KB = 1000000 bit).

Bps
“Byte per second” computers generally display speed in BPs, but sometimes it is confused with transmission speed. For example, ADSL claims that the bandwidth is 1Mbps, but in practical applications, the download speed is not 1MB, only 1Mbps / 8 = 128kbps
That is to say, B related to transmission speed generally refers to bit.
B related to capacity generally refers to byte.

PPS – packet forwarding rate
Packet forwarding rate indicates the capacity of the switch to forward packets. The unit is general bit PPS (packet per second), and the packet forwarding rate of general switch ranges from tens of kpps to hundreds of MPPs. Packet forwarding rate refers to the number of millions of packets (MPPs) that can be forwarded by the switch per second, that is, the number of packets that can be forwarded by the switch at the same time.
Packet forwarding rate reflects the exchange capability of the switch in terms of packets.

Gbps – backplane bandwidth
The backplane bandwidth of a switch is the maximum amount of data that can be handled between the switch interface processor or interface card and the data bus. The backplane bandwidth marks the total data exchange capacity of the switch, in Gbps, also known as the switching bandwidth. The backplane bandwidth of general switches varies from several Gbps to hundreds of Gbps. The higher the backplane bandwidth of a switch, the stronger the ability to process data, but the higher the design cost.

The availability of backplane bandwidth of a switch can be judged from the following two aspects:
1. (capacity of all ports × number of ports × 2) less than or equal to the backplane bandwidth can realize full duplex non blocking switching, which proves that the switch has the condition of maximum data switching performance.
2. Full configured throughput (MPPs): the number of full configured Ge ports × 1.488mpps, in which the theoretical throughput of one Gigabit port is 1.488mpps when the packet length is 64 bytes.

Theoretical throughput of Ge port -1.488mpps
The minimum packet length for Ethernet transmission is 64 bytes. The measurement of packet forwarding speed is based on the number of packets (minimum packets) that are sent in 64bytes per unit time.

For Gigabit Ethernet, the calculation method is as follows:

1000Mbps/((64B+8B+12B)×8bit)=1.488095pps

Note: when the Ethernet frame is 64BYTE, the fixed overhead of 8byte preamble and 12byte frame gap should be considered.
In Ethernet, each frame header is added with an 8-byte preamble, which is used to tell the monitoring device that data is coming. Then, there must be a frame gap between each frame in Ethernet, that is to say, after each frame is sent, one frame needs to wait for a period of time to send another frame. In the Ethernet standard, the minimum is 12 bytes. However, the frame gap may be larger than 12 bytes in practical application. Here I use the minimum value. Each frame has a fixed overhead of 20 bytes. (in addition, the 20 bytes of information cannot be captured by the packet capturing software.)
Therefore, the packet forwarding rate of a full duplex line speed Gigabit Ethernet port is 1.488mpps when forwarding 64BYTE packets.

The following are packet forwarding rates for common Ethernet ports:

1. 10 Gigabit Ethernet: 14.88mpps
2. Gigabit Ethernet: 1.488mpps
3. 100M Ethernet: 0.1488mpps

Packet forwarding rate indicates the capacity of the switch to forward packets. The unit is general bit PPS (packet per second), and the packet forwarding rate of general switch ranges from tens of kpps to hundreds of MPPs. Packet forwarding rate refers to the number of millions of packets (MPPs) that can be forwarded by the switch per second, that is, the number of packets that can be forwarded by the switch at the same time. Packet forwarding rate reflects the exchange capability of the switch in terms of packets.
The backplane bandwidth of a switch is the maximum amount of data that can be handled between the switch interface processor or interface card and the data bus. The backplane bandwidth marks the total data exchange capacity of the switch, in Gbps, also known as the switching bandwidth. The backplane bandwidth of general switches varies from several Gbps to hundreds of Gbps. The higher the backplane bandwidth of a switch, the stronger the ability to process data, but the higher the design cost.

So generally speaking, BPS is used for the second layer capability and PPS is used for the third layer capability. For devices supporting the third layer switching, manufacturers will provide the second layer forwarding rate and the third layer forwarding rate respectively.

In addition, let’s talk about how PPS is calculated
We know that the line speed packet forwarding rate of a Gigabit port is 1.4881mpps,
The line speed packet forwarding rate of 100m port is 0.14881mpps, which is an international standard, but how to get it?
During the transmission of specific packets, 64 preamble (leading symbol) will be added to the front of each packet, that is, a 64 byte packet,
Originally, there were only 512 bits, but in the process of transmission, there would be 512 + 64 + 96 = 672bit, that is, the length of a packet is actually
With 672 bit Gigabit port line speed packet forwarding rate = 1000Mbps / 672 = 1.488095mpps, which is about 1.4881mpps, 100MB divided by 10
0.14881mpps
Then it will be very simple. In fact, directly multiplying the PPS value in the device parameters by 672 will transform it into a popular BPS concept that we can understand.
General sales in order to facilitate your calculation and integer understanding of 672 to 500.