Calculation of backplane bandwidth and packet forwarding rate for switches in each layer.

For a large surveillance project, the focus is the choice of switches. Here we choose a layer three network architecture, network structure for the access layer aggregation layer and core layer. Relative to the layer two network architecture, the scale of the layer three architecture network is larger, the transmission distance is farther, and the scalability is higher.

The topology is as follows.

If the switch allocation is not reasonable, in some-sized networks, there will be lag or drop from time to time and even cause system paralysis. Therefore, the reasonable selection and allocation of switches in the access layer, aggregation layer and core layer are crucial. And the key points of the switch selection lie in the brand and the parameters of the switch itself.

For the use of the access layer switch, if the project itself is not very large, you can use some easy-to-use (fool) switches. It most uses 100 Megabit switches in general projects, of which the number of connected terminals does not exceed 8pcs. If the number of terminals is over 8pcs, it recommends a Gigabit Uplink switch.

The aggregation layer carries the high pressure of the connection with the access layer and core layer. It needs to consider the viewing bandwidth of the simultaneous-processing monitoring video.

Step 1, confirm the bandwidth of switches in the aggregation layer.

If there are 1000 IP cameras and 8 aggregation switches, each switch handles a total of 500M of data rate from 125 cameras (125* 4M=500M). That requests the aggregation switch should support simultaneous forwarding of over 500M switching capacity. A general Gigabit switch is meeting the requirement.

Step 2, confirm the backplane bandwidth of switches in the aggregation layer.

To ensure sufficient bandwidth, the requirement of backplane bandwidth to a 16-port Gigabit switch is (16*1000M*2)/1000=32Gbps.

Step 3, confirm the packet forwarding rate.

The packet forwarding rate of a 1000M port is 1.488Mpps/s. The packet forwarding rate of a 16-port aggregation switch is 16*1.488Mpps/s=23.44Mpps.

According to the above conditions, if a 16-port Gigabit switch is selected for the aggregation layer, the aggregation layer needs to meet the backplane bandwidth of at least 32Gbps and the packet forwarding rate of at least 23.44Mpps.

The core switch plays the role of the data forwarding and network structure setting.

The core switch is mainly responsible for data forwarding and network architecture setting and has higher requirements for switching capacity, network management functions, and stability. In addition, because the storage device is on the core layer, it also needs to consider the switching capacity of the switch, as well as the bandwidth and high-speed forwarding capacity of the link to the core.

Following conditions should be met.

Bandwidth

The bandwidth of 1000-channel monitoring is at least 1000*4Mbps=4000Mbps. The core switch is recommended to choose high-bandwidth Gigabit or 10GbE switch with 10GbE uplink port in order to make the data flow smoothly.

Backplane bandwidth

If a total of 12 gigabit ports with two 10Gigabit ports will be in use, in order to ensure sufficient bandwidth, the backplane bandwidth requirement of core switch is (12*1000M*2+2*10000*2)/1000=64Gbps.

Packet forwarding rate

The packet forwarding rate of a 1000M port is 1.488Mpps/s, a 10G port is 14.88Mpps/s.

In order to ensure line speed forwarding, there will be at least 12 Gigabit ports and two 10Gigabit ports, then the core switch forwarding rate is 12*1.488Mpps/s+2*14.88Mpps/s=47.56Mpps.

According to the above conditions: when there are 1000 cameras access to the network, the core layer switches need to meet at least 64Gbps backplane bandwidth, packet forwarding rate of at least 47.56Mpps.

In the actual project, if the 12 ports of the core switch are connected to full-load equipment, to ensure that the switch is not under full load as well as its scalability, we'd better use a 16-port, or 24-port Gigabit interface, two up-connected 10 Gigabit ports of the core switch. The required backplane bandwidth and packet forwarding rate are higher. This switch capacity and packet forwarding rate are more than sufficient to ensure the project data exchange at high speed.

In addition to the backplane bandwidth and packet forwarding rate of the switch, its performance is still influenced by quite a several factors, such as scalability, number of slots, module type, module redundancy, routing redundancy, etc. Especially on the scale of the network monitoring project, we need to calculate the backplane bandwidth and packet forwarding rate when choosing a switch to ensure the system works stably and reliably, keeping the image away from the interrupt and reducing the occurrence of failure.