In fact, regarding the choice of switches, we have mentioned it in the previous section. Today we will use a detailed example to understand the choice of switches, taking 500-channel monitoring how to choose a switch as an example.
First, the basic understanding
When understanding the choice of switches, let's add some basic knowledge:
Camera code stream: Before selecting a switch, you must first figure out how much bandwidth each image takes up, and this is the code stream.
Number of cameras: To figure out the bandwidth capacity of the switch. Common switches have hundreds of megabytes of switches and gigabit switches. Their actual bandwidth is generally only 60 to 70% of the theoretical value, so the available bandwidth of their ports is roughly 60Mbps or 600Mbps.
Example
Look at the single stream based on the brand of the network camera you are using, and then estimate how many cameras a switch can pick up. such as:
1.3 million: 960p camera single stream is usually 4M, with 100M switch, then you can connect 15 (15 × 4 = 60M); with Gigabit switch, you can connect 150 (150 × 4 = 600M).
2 million: 1080P camera single stream is usually 8M, with 100M switch, you can connect 7 (7 × 8 = 56M); with Gigabit switch, you can connect 75 (75 × 8 = 600M) These are the mainstream The H.264 camera is an example for everyone to explain, H.265 is halved.
Second, 500 way monitoring how to choose a switch
Example: How to select a switch for 500-channel monitoring
For example, there is a campus network, more than 500 high-definition cameras, and a code stream of 3 to 4 megabytes. The network structure is divided into the core layer of the access layer convergence layer. Stored in the aggregation layer, each aggregation layer corresponds to 170 cameras.
The problem: how to choose the product, the difference between 100 Mbps and Gigabit, what are the reasons for the image transmission in the network, and what factors are related to the switch...
You can see the topology diagram as follows:
1. 500-channel monitoring access layer switch
The first 500 cameras, the code stream of each camera is 4M.
1. Condition 1: Camera code stream: 4 Mbps, 10 cameras are 10*4=40 Mbps.
That is to say, the access port of the access layer switch must meet the transmission rate requirement of 40Mbps/s, considering the actual transmission rate of the switch (usually 50% of the nominal value, 50M of 100M), so a hundred megabytes The switch can carry 10 cameras, 500 channels can be used to access the layer to use 50 100M switches, of course, can also be calculated by Gigabit switches.
2. Condition 2: The backplane bandwidth of the switch. If a 16-port 100-Mbps switch is selected, the bandwidth requirement of the switch backplane of the access layer is: (16*100M*2)/1000=3.2Gbps backplane bandwidth.
3. Condition 3: Packet forwarding rate: The packet forwarding rate of a 1000M interface is 1.488 Mpps/s, and the switching rate of the access layer is: (16*100M/100M)*0.1488=2.368Mpps.
According to the above conditions: When there are 500 cameras accessing the network, 50 100M access switches are required at this time, and the backplane bandwidth needs to be greater than 3.2Gbps, and the packet forwarding rate is greater than 2.368Mpps.
Second, the choice of the aggregation layer switch
The aggregation layer is up and down, and the pressure is the biggest. It is necessary to consider the bandwidth of the monitoring and viewing at the same time.
If there are 500 cameras in the aggregation layer and there are three switches in the aggregation layer, each of them needs to process the 4M stream (170* 4M=680M) of 170 cameras at the same time, which means that the aggregation layer switch needs to support the exchange of 680M or more at the same time. capacity. In this case, the general Gigabit switch can be said to be just enough (if in the actual project, if the budget is sufficient, the aggregation layer should use 4 switches as much as possible).
Generally, the storage is connected to the aggregation, so the video recording is wire-speed forwarding. However, considering the bandwidth of real-time monitoring, each connection occupies 4M, a 1000M link is practical 600M, and 150 cameras are supported for debugging. Each access switch is connected to 10 cameras, 150/10, which is equivalent to the network can withstand the pressure of 15 users in real time viewing each camera.
Third, the choice of the core layer switch
The core switch needs to consider the switching capacity and the link bandwidth to the aggregation. Because the storage is placed at the aggregation layer, the core switch does not have the pressure of video recording, that is, just consider how many people watch video at the same time. Assume that in this case, there are 10 people watching at the same time, each person watching 16 channels of video, that is, the exchange capacity needs to be greater than 10*16*4=640M.
supplement:
When video surveillance in the LAN is selected for the switch, the choice of the access layer and the aggregation layer switch usually only needs to consider the factor of the switching capacity, because the user usually connects and acquires the video through the core switch. In addition, since the main pressure is at the aggregation layer switch, it is very important to select the applicable aggregation switch because it has to bear the monitoring of the stored traffic and the pressure to view the monitoring in real time.
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