Backplane Bandwidth and Calculation Method of Industrial Switch

The backplane bandwidth of the Industrial Switch is the maximum amount of data that can be throughput between the switch interface processor or the interface card and bus.The backplane bandwidth indicates the total data exchange capacity of the industrial switch, and the unit is Gbps, also called the switching bandwidth. The backplane bandwidth of a general industrial switch ranges from several Gbps to hundreds of Gbps.The higher the backplane bandwidth of an industrial switch, the stronger the ability to process data, but the higher the design cost.

The utilization of backplane bandwidth resources is closely related to the internal structure of the industrial switch.The internal structure of the industrial switch mainly includes the following: First, the shared memory structure, which relies on the central switching engine to provide high-performance connections of all ports, and the core engine checks each input packet to determine the route.This method requires large memory bandwidth and high management costs, especially with the increase of industrial switch ports, the price of the central memory will be high, so the cow of the industrial switch becomes the bottleneck of performance realization; the second is the cross bus structure, which A direct point-to-point connection can be established between ports, which is very good for single-point transmission, but not suitable for multi-point transmission; the third is the hybrid crossover bus structure, which is a hybrid crossover bus implementation. The integrated cross-bus matrix is divided into small cross-matrixes, which are connected by a high-performance bus in the middle.The advantage is that the number of crossover buses is reduced, the cost is reduced, and the bus contention is reduced; but the bus connecting the crossover matrix becomes a new performance bottleneck.

When purchasing an industrial switch, you can also calculate the backplane bandwidth through a formula based on the number of ports and port rates to determine whether the industrial switch meets the requirements and whether it is a wire-speed switch. How to calculate it specifically?

   1) Line-speed backplane bandwidth

Calculate the total network bandwidth available from all port numbers on the industrial switch.The calculation method is the number of ports * relative port number speed * 2 (full duplex mode) If the total network bandwidth ≤ tolerance backplane bandwidth, then the backplane bandwidth is wire-speed.

    2) Layer 2 packet forwarding wire speed

The second layer packet forwarding rate = the total number of Gigabit network card port numbers × 1.488Mpps + the total number of 100M port numbers * 0.1488Mpps + the number of other types of ports * relative calculation method, if this speed can be less than or equal to the tolerance layer two packet forwarding speed, then the industry The switch can guarantee the wire speed in the case of doing the second layer exchange.

    3) Layer 3 packet forwarding wire speed

The third-layer packet forwarding rate = the total number of gigabit network card port numbers × 1.488Mpps + the total number of 100-megabit port numbers * 0.1488Mpps + the number of other types of ports * relative calculation method, if this speed can be less than or equal to the tolerance of the three-layer packet forwarding speed, then the industrial The switch can guarantee the wire speed in the case of doing Layer 3 interchange.

So, how did the gigabit port packet forwarding rate of 1.488Mpps get it?

The evaluation index of the packet forwarding line speed is based on the number of 64byte data files pushed per unit time as the measurement standard.For Gigabit Ethernet, the calculation is as follows:

1000000000/8/(64+8+12)=1 488 095.2380952pps is 1.488Mpps, of which 1000000000: 100Mbps port transmission rate, the first 8: 8 bits per byte; 64: the minimum length of the Ethernet frame; Two 8: Ethernet frame preamble, 12: frame gap

When the Ethernet frame is 64byte, consider 8byte frame header and 12byte frame gap Of the fixed overhead. So a wire-speed Gigabit Ethernet port forwarding 64byte packet when the packet forwarding rate of 1.488Mpps. Fast Ethernet’s wire-speed port packet forwarding rate is exactly one-tenth of Gigabit Ethernet, which is 148.8kpps.

* For 10 Gigabit Ethernet interfaces, the packet forwarding rate of a wire-speed port number is 14.88Mpps.

* For Gigabit Ethernet, the packet forwarding rate of a wire-speed port number is 1.488Mpps.

* For a Fast Ethernet interface, the packet forwarding rate of a wire-speed port number is 0.1488Mpps.

Therefore, if the above three standards can be considered, then we can say that the industrial switch truly guarantees linearity and no blockage.Therefore, when purchasing an industrial switch , it is necessary to select a switch that can meet the requirements of the backplane bandwidth and packet forwarding rate according to the number of ports and port rate of the switch, otherwise it will easily form a bottleneck in the system.