In order to be able to load the increasingly complex video surveillance system network, the switch needs to access more cameras, and the larger the data volume of the switch. The switch must have a very stable ability to convert data to transmit large amounts and continuously Video data. So, should the ethernet switch choose 100M or 1000M?

The data transmitted per unit time during data transmission is called the code stream, if the amount of data forwarded by the camera under the switch exceeds the forwarding capacity of a certain port, it will also cause this port to discard a large amount of data and cause problems.

For example, a 100M switch forwards a data volume exceeding 100M, which will cause a large amount of packet loss, resulting in screen freezes. So, how many cameras do you need to choose a gigabit switch?

There is a standard, depending on the amount of data forwarded by the camera’s uplink port: if the amount of data forwarded by the uplink port is greater than 70M, choose a gigabit port, that is, choose a gigabit switch or a gigabit uplink switch.

There is a quick calculation and selection method: bandwidth value = (sub stream + main stream) * number of channels * 1.2:

① Bandwidth value> 70M, use gigabit;

②Bandwidth value <70M, use 100M.

Question 1: The code stream calculation process is very clear, but why should it be multiplied by 1.2?

Because according to the principle of network communication, the encapsulation of data packets also follows the TCP/IP protocol, and the data part needs to be marked with the header fields of each protocol layer to be transmitted smoothly, so the header will also occupy a certain proportion of the overhead.
The 4M bit rate and 2M bit rate of the camera we often talk about refers to the size of the data part. According to the data communication ratio, the head overhead accounts for about 20%, so the formula has to be multiplied by 1.2.

Question 2: Why is 70M not 100M?

Mainly to consider burst traffic. The video data stream is composed of a lot of frames. The seemingly smooth data stream actually has many instantaneous bursts of data. This situation requires the switch to buffer and rectify the fluctuation of the data.
The switch stores-forward-store-forward these data, so it is recommended to have a certain reservation. When designing the switching network, there can be 30%-40% reservation. For a 100M port, it is recommended that the forwarding traffic does not exceed 70M.

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