Today we use the case to see how to select the switch in the monitoring system.
Case:
There is a campus network, more than 500 high-definition cameras, stream 3 to 4 trillion, the network structure is divided into access layer - convergence layer - core layer. Stored at the aggregation layer, each convergence layer corresponds to 170 cameras.
We must first understand these issues:
How to choose a product, reason. The difference between Gigabit and Gigabit. What are the reasons that affect the transmission of images in the network? Which are related to the switch.
Backplane bandwidth
The sum of all port capacity X port numbers should be less than the backplane bandwidth, enabling full-duplex non-blocking wire-speed switching, proving that the switch has the maximum data exchange performance.
For example: a switch that can provide up to 48 Gigabit ports, the full configuration capacity should reach 48 × 2G × 2 = 192Gbps, to ensure non-blocking wire-speed packet switching when all ports are in full duplex .
Packet forwarding rate
Full configuration packet forwarding rate (Mbps) = full configuration of GE ports × 1.488Mpps + full configuration 100M ports × 0.1488Mpps, of which a Gigabit port has a theoretical throughput of 1.488Mpps when the packet length is 64 bytes.
E.g:
If a switch can provide up to 24 Gigabit ports and the advertised 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 is designed with a blocked architecture.
A switch that is generally both satisfied is a qualified switch
Relatively large backplanes and relatively small throughput switches, in addition to retaining the ability to upgrade and expand, are software efficiency/dedicated chip circuit design issues;
Relatively small backplanes and relatively high throughput switches have relatively high overall performance.
Camera stream
The factors that affect the definition are usually the code stream settings of the video transmission (including the coding and decoding capabilities of the coded transmission and receiving equipment, etc.). This is the performance of the front-end camera and has nothing to do with the network. .....
Usually the user thinks the clarity is not high, and it is actually a misunderstanding to think that the idea caused by the network causes.
A Gigabit link can support data transmission
Calculation: Stream: 4Mbps
Access: 24*4=96Mbps<1000Mbps<4435.2Mbps
Convergence: 170*4=680Mbps<1000Mbps<4435.2Mbps
Access switch
The access layer switch mainly considers the link bandwidth between access and aggregation. That is, the uplink link capacity of the switch needs to be greater than the number of video cameras* that are accommodated at the same time. In this way, there will be no problem with real-time video recording. However, if a user sees the video in real time, the bandwidth needs to be taken into account. The bandwidth occupied by each user to view a video is 4 M. If each camera of an access switch is When one person is watching, it needs the bandwidth of the camera *bit rate*(1+N).
24*4*(1+1)=128M
Aggregation layer switch
At the convergence layer, it is necessary to process the 3-4M code stream of 170 cameras at the same time (170*4M=680M), which means that the convergence layer switch needs to support switching capacity of more than 680M at the same time. General storage is connected to the convergence, so video recording is wire-speed forwarding.
But to take into account real-time viewing of monitored bandwidth, each connection occupies 4M, and a 1000M link can support 250 cameras to be debugged. Each access switch connects 24 cameras. 250/24, the equivalent of the network can withstand the pressure of each camera at the same time 10 users in real-time viewing.
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 convergence layer, so the core switch does not have the pressure of video recording, that is, it only needs to consider how many people watch the video at the same time. Assuming that there are 10 people monitoring the case at the same time, each person sees 16 videos, that is, the exchange capacity needs to be greater than 10*16*4=640M, basically no need to consider.
When the video surveillance in the LAN is used for switch selection, the selection of the access layer and convergence layer switch usually only needs to consider the exchange capacity factor. Because users are usually connected through the core switch and get video.
Switch selection
When the video surveillance in the LAN is used for switch selection, because the main pressure is at the aggregation layer switch, the aggregation layer switch must not only monitor the storage traffic, but also bear the pressure of real-time viewing call monitoring. Therefore, it is very important to choose the applicable aggregation switch.
For the access switch, there is no essential difference between the ports that connect the cameras to the downstream ports at 100Mbit/Gigabit, but the uplink must be Gigabit.
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