In the project, some friends often ask how to choose switches in large monitoring systems. The choice of switches has been a problem for many friends, so today we use cases to understand how large monitors choose switches.
There is a campus network, more than 500 HD cameras, 3~4 streams, and the network structure is divided into access layer convergence layer core layer. Stored in the convergence layer, each convergence layer corresponds to 170 cameras.
How to choose the product and the reason.
The difference between a hundred megabytes and a Gigabit.
What are the reasons that affect the transmission of images in the network?
Which is related to the switch.
The 2 times the sum of all port capacity X ports should be less than the backplane bandwidth, and can achieve full duplex non blocking line speed exchange, proving that the switch has the condition that the maximum data exchange performance is played.
For example, a switch with up to 48 Gigabit ports, with a full configuration capacity of 48 * 2G x 2= 192Gbps, can ensure that no blocking line speed packet switching is provided at full duplex at all ports.
Packet forwarding rate
Full configuration packet forwarding rate (Mbps) = full configuration GE port number x 1.488Mpps+ full megabyte number x 0.1488Mpps, of which 1 Gigabit ports in the packet length is 64 bytes, the theoretical throughput is 1.488Mpps.
If a switch can provide up to 24 Gigabit ports, and the declared packet forwarding rate is less than 35.71 Mpps (24 x 1.488Mpps = 35.71), there is a reason to think that the switch uses a blocked structure design.
Generally speaking, the switches that satisfy both are qualified switches.
The switch with relatively large backplane and relatively small throughput is the problem of software efficiency / special chip circuit design in addition to the ability to upgrade and expand.
The backplane is relatively small with relatively high throughput, and the overall performance is relatively high.
The factors that affect the clarity are usually the stream setting of the video transmission (including the coding and decoding capabilities of the transmitting and receiving devices, etc.), which is the performance of the front end camera and has nothing to do with the network. ...
Usually the user thinks that the definition is not high, and the idea that it is caused by the network is actually a misunderstanding.
A Gigabit link can support data transmission
Bit stream: 4Mbps
The access layer switch mainly takes account of the link bandwidth between access and convergence. That is to say, the upper link capacity of the switch needs to be larger than the number of cameras at the same time. In this way, video real-time video is no problem, but if a user sees the video in real time, it needs to take into account the bandwidth. Each user looks at a video occupying a bandwidth of 4M. If every camera in an access switch is looking, it needs the bandwidth of the camera number * (1+N).
24*4* (1+1) =128M
The 3-4M code stream (170* 4M=680M) that requires simultaneous processing of 170 cameras at the aggregation layer means that the converge layer switch needs to support the simultaneous forwarding of the switching capacity of more than 680M. General storage is connected to the convergence, so video recording is line speed forwarding.
But in order to see the bandwidth of monitoring in real time, each link takes up 4M and a 1000M link can support 250 cameras to be called for debugging. Each switch is connected to 24 cameras. 250/24, equivalent to the network can withstand the pressure of 10 cameras per camera in real time.
The core switch needs to consider the exchange capacity and the link bandwidth, because the storage is placed in the aggregation layer, so the core switch has no video video pressure, that is, as long as considering how many people watch the road video at the same time. Suppose that in the case, 10 people watched at the same time, each of them watched 16 videos, that is, the exchange capacity should be greater than 10*16*4=640M, which basically need not be considered.
When the switch is selected for video monitoring in LAN, the selection of access layer and converging layer switch usually only needs to consider the factors of exchange capacity. Because users usually connect and acquire video through core switches.
Key to switch selection
When the video monitoring system is selected in the LAN, the main pressure is in the convergent layer switch, and the converging layer switch is not only responsible for the traffic monitoring and storage, but also the pressure of real-time view call monitoring. So it is very important to choose the appropriate converging switch.
For access switches, there is no essential difference between the ports of the lower ports and the ports of the cameras, but the upper couplet must be Gigabit.
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