How to choose a switch in the monitoring system

Compared with analog video surveillance, high-definition network video surveillance replaces coaxial cable with twisted pair cable, and the transmission of twisted pair cable depends on the switch. With the application of high-definition network video surveillance more and more, how to choose the switch is the user. For more concerned issues, let's use the case to find out how to choose a switch.

1, for example

There is a campus network, more than 500 high-definition cameras, and the code stream is 3~4 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...

The sum of all port capacity x port numbers should be less than the nominal backplane bandwidth, enabling full-duplex non-blocking wire-speed switching, proving that the switch has the conditions for maximum data exchange performance. For example, a switch with up to 48 Gigabit ports should have a full configuration capacity of 48 × 1G × 2 = 96Gbps to ensure non-blocking wire-speed packet switching when all ports are in full duplex. .

2, packet forwarding rate

Full configuration packet forwarding rate (Mbps) = full configuration GE port number × 1.488 Mpps + full configuration 100 Mbps port number × 0.1488 Mpps, of which 1 gigabit port has a theoretical throughput of 1.488 Mpps when the packet length is 64 bytes.

For example, if a switch can provide up to 24 Gigabit ports and the claimed packet forwarding rate is less than 35.71 Mpps (24 x 1.488 Mpps = 35.71), then there is reason to believe that the switch uses a blocking structure design.

Generally, a switch with a backplane bandwidth and a packet forwarding rate is a suitable switch. A switch with a relatively large backplane and relatively small throughput, in addition to retaining the ability to upgrade and expand, is a problem with software efficiency/special chip circuit design; a switch with a relatively small backplane and relatively large throughput has a relatively high overall performance.

The camera stream affects the definition, usually the stream setting of the video transmission (including the encoding and decoding capabilities of the encoding transmitting and receiving devices, etc.), which is the performance of the front-end camera, independent of the network.

Usually, users think that the definition is not high, and the idea that is caused by the network is actually a misunderstanding.

According to the above case, calculate:

Code stream: 4Mbps

Access: 24*4=96Mbps<1000Mbps<4435.2Mbps

Convergence: 170*4=680Mbps<1000Mbps<4435.2Mbps

3. Access switch

The link bandwidth between access and aggregation is mainly considered, that is, the uplink link capacity of the switch needs to be larger than the number of cameras * code rate accommodated at the same time.

In this way, video real-time recording is no problem, but if a user sees the video in real time, it needs to consider this bandwidth. The bandwidth occupied by each user to view a video is 4M, if each camera of an access switch is If one is watching, you need the camera's *code rate*(1+N) bandwidth, which is 24*4*(1+1)=128M.

4, aggregation switch

The aggregation layer needs to process the 34M code stream of 170 cameras (170* 4M=680M) at the same time, which means that the aggregation layer switch needs to support the forwarding capacity of 680M or more at the same time. 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, and a 1000M link can support 250 cameras to be debugged. Each access switch is connected to 24 cameras, 250/24, which is equivalent to the network can withstand the pressure of real-time viewing of 10 cameras per user at the same time.

5, the core 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.

6, switch selection focus

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.

The above is all the answers to how to choose the switch in the monitoring system. For more information, please pay attention to Tengyuan Zhituo. If you have any needs or questions in this regard, please feel free to ask our customer service staff.