How many network surveillance cameras can a switch drive ? How many Gigabit switches can be connected to 2 million network cameras? 24 network heads, is it okay to use a 24-port 100M switch? Let's do some simple analysis on this kind of problem!
1. Choose according to the code stream and quantity of the camera
1. Camera stream
Before choosing a switch, you must first figure out how much bandwidth each image takes.
2. Number of cameras
To find out the bandwidth capacity of the switch. Commonly used switches include 100M switches and Gigabit switches. Their actual bandwidth is generally only 60~70% of the theoretical value, so the available bandwidth of their ports is roughly 60Mbps or 600Mbps.
Example:
According to the brand of network camera you use, look at the single bit stream, and then estimate how many cameras can be connected to a switch.
For example, 1.3 million: a single 960p camera’s code stream is usually 4M, and if you use a 100M switch, you can connect 15 sets (15×4=60M);
With a Gigabit switch, you can connect 150 (150×4=600M)
2 million: a single 1080P camera stream is usually 8M, with a 100M switch, you can connect 7 sets (7×8=56M);
With Gigabit switches, you can connect 75 sets (75×8=600M)
These are all explained by taking the mainstream H.264 camera as an example, and H.265 can be halved.
In terms of network topology, a LAN is usually a two- to three-layer structure. The end connected to the camera is the access layer, generally a 100M switch is enough, unless you connect many cameras to one switch.
The aggregation layer and the core layer are calculated according to how many channels of images are aggregated by the switch.
The calculation method is as follows:
If you connect a 960P network camera, generally use a 100M switch for less than 15 channels of images; use a Gigabit switch for more than 15 channels; Gigabit switch.
Selection of weak current products,,,
H3C switch configuration video tutorial detailed explanation
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Second, the selection requirements of the switch
The monitoring network has a three-layer architecture: the core layer, the aggregation layer, and the access layer.
1. Selection of access layer switches
Condition 1: Camera stream: 4Mbps, 20 cameras is 20*4=80Mbps.
That is to say, the upload port of the access layer switch must meet the transmission rate requirement of 80Mbps/s. Considering the actual transmission rate of the switch (usually 50% of the nominal value, 100M is about 50 M), so the access layer The switch should use a switch with a 1000M upload port.
Condition 2: The backplane bandwidth of the switch, if a 24-port switch is selected, with two 1000M ports, a total of 26 ports, then the bandwidth requirement of the switch backplane at the access layer is: (24*100M*2+1000*2*2 )/1000=8.8Gbps backplane bandwidth.
Condition 3: Packet forwarding rate: the packet forwarding rate of a 1000M port is 1.488Mpps/s, then the switching rate of the switch at the access layer is: (24*100M/1000M+2)*1.488=6.55Mpps.
According to the above conditions: when 20 channels of 720P cameras are connected to a switch, the switch must have at least one 1000M upload port and more than 20 100M access ports to meet the requirements.
2. Selection of aggregation layer switches
If there are a total of 5 switches connected, each switch has 20 cameras, and the code stream is 4M, then the traffic at the aggregation layer is : 4Mbps*20*5=400Mbps, then the upload port of the aggregation layer must be above 1000M.
If 5 IPCs are connected to a switch, generally an 8-port switch is required, does this 8-port switch meet the requirements? It can be seen in the following three aspects:
Backplane bandwidth: number of ports*port speed*2=backplane bandwidth, that is, 8*100*2=1.6Gbps.
Packet exchange rate: number of ports*port speed/1000*1.488Mpps=packet exchange rate, that is, 8*100/1000*1.488=1.20Mpps. The packet exchange rate of some switches is sometimes calculated to fail to meet this requirement, so it is a non-wire-speed switch, and it is easy to cause delay when performing large-capacity throughput.
Cascading port bandwidth: IPC code stream * quantity = minimum bandwidth of upload port, that is, 4.*5=20Mbps. Normally, when the IPC bandwidth exceeds 45Mbps, it is recommended to use a 1000M cascade port.
3. How to choose a switch
1. Examples
There is a campus network with more than 500 high-definition cameras and a bit stream of 3-4 megabytes. The network structure is divided into access layer-aggregation layer-core layer. It is stored in the aggregation layer, and each aggregation layer corresponds to 170 cameras.
Problems faced: how to choose products, the difference between 100M and 1000M, what are the reasons that affect the transmission of images in the network, and what factors are related to switches...
Twice the sum of all port capacity x port quantity should be less than the nominal backplane bandwidth, which can realize full-duplex non-blocking wire-speed switching, proving that the switch has the conditions to maximize data switching performance.
For example: a switch that can provide up to 48 Gigabit ports, its full configuration capacity should reach 48 × 1G × 2 = 96Gbps, in order to ensure non-blocking wire-speed packet switching when all ports are in full duplex .
2. Packet forwarding rate
Fully configured packet forwarding rate (Mbps) = fully configured number of GE ports × 1.488Mpps + fully configured 100M port number × 0.1488Mpps, and the theoretical throughput of one Gigabit port is 1.488Mpps when the packet length is 64 bytes.
For example: 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), then it is reasonable to think that the switch is designed with a blocking structure .
Generally, the switch that satisfies both the backplane bandwidth and the packet forwarding rate is the appropriate switch.
A switch with a relatively large backplane and a relatively small throughput, in addition to retaining the ability to upgrade and expand, has problems with software efficiency/special chip circuit design; a switch with a relatively small backplane and a relatively large throughput has relatively high overall performance.
The camera bit stream affects the definition, usually the bit stream setting of the video transmission (including the encoding and decoding capabilities of the encoding sending and receiving equipment, etc.), which is the performance of the front-end camera and has nothing to do with the network.
Usually users think that the clarity is not high, and the idea that it is caused by the network is actually a misunderstanding.
Based on the above example, calculate:
Code stream: 4Mbps
Access: 24*4=96Mbps<1000Mbps<4435.2Mbps
Convergence: 170*4=680Mbps<1000Mbps<4435.2Mbps
3. Access switch
The main consideration is the link bandwidth between access and aggregation, that is, the uplink capacity of the switch needs to be greater than the number of cameras that can be accommodated at the same time*bit rate.
In this way, there is no problem with real-time video recording, but if some users watch the video in real time, this bandwidth must also be taken into account. The bandwidth occupied by each user to view a video is 4M. If each camera connected to the switch has If one person is watching, the bandwidth of the number of cameras*bit rate*(1+N) is needed, that is, 24*4*(1+1)=128M.
4. Aggregation switch
The aggregation layer needs to process the 3-4M code streams of 170 cameras at the same time (170* 4M=680M), which means that the aggregation layer switch needs to support the switching capacity of more than 680M forwarding at the same time. Generally, storage is connected to the convergence, so video recording is forwarded at wire speed.
However, considering the bandwidth of real-time viewing and monitoring, each connection occupies 4M, and a 1000M link can support 250 cameras to be debugged and called. Each access switch is connected to 24 cameras, 250/24, which means that the network can withstand the pressure of 10 users viewing each camera in real time at the same time .
5. Core switch
The core switch needs to consider the switching capacity and the link bandwidth to the aggregation layer. Because the storage is placed on the aggregation layer, the core switch does not have the pressure of video recording, that is, it only needs to consider how many people watch how many channels of video at the same time.
Assume that in this case, there are 10 people monitoring at the same time, and each person watches 16 channels of video, that is, the switching capacity needs to be greater than 10*16*4=640M.
6. Switch selection focus
When selecting switches for video surveillance in the LAN, the choice of access layer and aggregation layer switches usually only needs to consider the factor of switching capacity, because users usually connect and obtain video through core switches.
In addition, since the main pressure is on the aggregation layer switch, it is very important to choose an appropriate aggregation switch because it is not only responsible for monitoring the traffic of the storage, but also bears the pressure of real-time viewing and monitoring.
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