In combination with the above factors, the following factors need to be considered when choosing a monitoring switch:
1. Number and speed of ports
The number and speed of the switch interfaces are the most important indicators for choosing a monitoring switch. The number of interfaces is determined by the number of access devices, and some interfaces can be appropriately reserved for subsequent network expansion. In order to ensure that video traffic is not blocked and transmitted in real time, it is necessary to select a switch with an appropriate port speed, mainly considering the following points:
The bandwidth of the monitoring switch is closely related to the bit stream size of the IPC;
The peak bandwidth requirement of the IPC = bit stream × 120%, and the stable use of the IPC can be guaranteed under the peak bandwidth;
After the NVR joins the IPC, it will simultaneously obtain the main bit stream and sub-bit stream of the IPC;
The actual bandwidth of the switch is recommended not to exceed 70% of the maximum rate of the port, that is, the 100M interface is not recommended to exceed 70M bandwidth, and the 1000M interface is not recommended to exceed 700M bandwidth.
Quick calculation formula: bandwidth value = (main bit stream + sub-bit stream) * number of streams * 1.2
Note: The above 1 and 2 are experimental test data. In addition to the bit rate, the main considerations are data transmission overhead and network fluctuations.
The bit rate of IPC is related to the encoding method (H.264 or H.265) used. By default, the bit rate of IPC is:
So in actual applications, where should 100M switches be selected and where should 1000M switches be selected? The following will analyze and explain through two common topologies.
Scenario 1: Multiple switches in series
In the figure below, three switches A, B, and C are connected one by one using network cables. Each switch is connected to 8 IPCs, and the NVR is connected to switch A to manage all IPCs at the same time.
Assuming that all IPCs have a main stream of 4M and a substream of 0.5M, then:
Cascade port 3# must meet the bandwidth sum of all IPCs on switch C, which is (4+0.5)×120%×8=43.2M, and cascade port 3# can use a 100M port;
Cascade port 2# must meet the bandwidth sum of all IPCs on switches B and C, which is (4+0.5)×120%×(8+8)=86.4M>70M, and cascade port 2# needs to use a Gigabit port;
Cascade port 1# must meet the bandwidth generated by all IPCs on switches A, B, and C. The bandwidth is (4+0.5)×120%×(8+8+8)=129.6M>70M. Cascade port 1# must use a Gigabit port;
So the switch selection in the above topology is: Switch C can choose a 100M switch, and switches B and A are recommended to use a Gigabit uplink (mixed Gigabit and 100M) switch.
Scenario 2: Multiple video recorders monitor all IPCs simultaneously
In the figure below, two NVRs are used for LAN monitoring (for example, one NVR is placed in the monitoring room and one in the front desk). Each switch is connected to 10 IPCs. The two NVRs are connected to switch A to manage all IPCs at the same time. Each IPC will receive two main streams and sub-streams at the same time.
According to the above calculation method, the bandwidth of cascade port 4# and cascade port 5# are both 86.4M, and the bandwidth of cascade port 3# is 172.8M (the bandwidth is doubled because two NVRs simultaneously take the stream), which are all over 70M, so switches B, C and D are recommended to use Gigabit uplink (mixed Gigabit and 100M) switches. The bandwidth of cascade port 1# and cascade port 2# are both 172.8M, and switch A has 4 ports that need to use Gigabit ports, so switch A is recommended to use a full Gigabit switch.
The following are switch selection recommendations based on the number of surveillance cameras and the main code stream bit rate, according to the above bandwidth calculation formula:
Note: If you choose a Gigabit uplink switch, the Gigabit port of the switch is connected to the front-end Gigabit network or the Gigabit interface of the NVR.
For example: There are 20 IPCs in the monitoring network, the main stream is 4M, and the sub-stream is 1M, then the total bandwidth = (4+1) × 20 × 1.2 = 120M, which exceeds 70M. You need to choose a Gigabit uplink switch and connect the Gigabit port of the switch to the NVR.
2. PoE power supply
In traditional network surveillance projects, centralized power supply is generally used to power surveillance cameras. In addition to high cost and complex construction, it also brings limitations such as wiring, power supply risks, and power supply distance. PoE power supply is an inevitable trend in security power supply. Only an ordinary network cable is needed to connect the PoE switch and the network camera to transmit data and supply power at the same time. As follows:
Advantages of PoE power supply:
Avoid additional wiring, neat and beautiful, save wiring costs;
PoE power supply voltage is high, transmission distance is longer and more stable.
Note: This power supply method requires the camera to also support PoE power supply.
