How many IP cameras can an Ethernet switch connect to? How many Gigabit switches can be connected to 2 million network cameras? Is it possible to use a 24-port 100M switch for 24 IP cameras? Let’s make an analysis on these problems!
Part I. Choose according to the bitstream and quantity of the camera
1. Camera bitstream
Before choosing a switch, the first thing you should do is to figure out how much bandwidth each image occupies.
2. Number of cameras
Then, you should know the bandwidth capacity of the switch. Commonly used switches are 100M switches and Gigabit switches, whose actual bandwidth is generally only 60~70% of the theoretical value. Therefore, the available bandwidth of their ports is roughly 60Mbps or 600Mbps.
Check the bitstream of a single camera according to the brand of your IP camera and then estimate how many cameras can be connected to a switch.
● For 1.3 million:
The bitstream per 960p camera usually is 4M. If a 100M switch is used, then 15 cameras can be connected (15×4=60M);
With a Gigabit switch, you can connect 150 sets(150×4=600M)
● For 2 million:
The bitstream of a 1080P IP camera usually is 8M. With a 100M switch, you can connect 7 units (7×8=56M);
With a Gigabit switch, you can connect 75 sets (75×8=600M)
These are all explained by taking the mainstream H.264 camera as an example, and the H.265 can be halved.
In terms of network topology, a local area network (LAN) is usually a two- to three-layer structure. The end that connects to the camera is the access layer and a 100M switch is sufficient unless you connect many cameras to one switch.
The aggregation layer and the core layer are calculated according to how many images the switch aggregates. Calculate as follows:
● If you connect a 960P IP camera within 15 approaches of images, generally you can use a 100M switch. If there are more than 15 approaches, you can use a Gigabit switch.
● If you connect a 1080P IP camera within 8 approaches of images, use a 100M switch. If there are more than 8 approaches, use a Gigabit switch.
Part II. What’s the requirement for choosing Ethernet switches?
The monitoring network has a three-layer architecture: core layer, aggregation layer, and access layer.
1. Access layer switches
Camera bitstream: 4Mbps, then 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 50M), the access layer should choose those with 1000M upload port.
If you choose a 24-port switch with two 1000M ports, the total is 26 ports. Then the backplane bandwidth of the switch at the access layer is (24*100M*2+1000*2*2 )/1000=8.8Gbps.
Packet forwarding rate: The packet forwarding rate of a 1000M port is 1.488Mpps/s, so the switching rate of the switch at the access layer should be (24*100M/1000M+2)*1.488=6.55Mpps.
According to the above conditions, when there are 20 720P cameras connected to a switch, the switch must have at least one 1000M upload port and more than 20 100M access ports.
2. Aggregation layer switches
If a total of 5 switches are connected, each switch has 20 cameras, and the bitstream is 4M, then the traffic of the aggregation layer is: 4Mbps*20*5=400Mbps. Thus, the upload port of the aggregation layer must be more than 1000M.
If 5 IPCs are connected to a switch, an 8-port switch is required generally. Could the 8-port switch meet the requirements? Check the following three aspects!
● Backplane bandwidth:
number of ports*port speed*2=backplane bandwidth
● Packet exchange rate:
number of ports*port speed/1000*1.488Mpps=packet exchange rate
Sometimes the packet exchange rate of some switches can’t be calculated to meet this requirement, then it is a non-wire-speed switch. It’s easy to cause delay when handling large-capacity quantities.
● Cascade port bandwidth:
IPC bitstream * quantity = minimum bandwidth of upload port
Normally, when the IPC bandwidth exceeds 45Mbps, it is recommended to use a 1000M cascade port.
Part III. How to choose an Ethernet switch?
There is a campus network and more than 500 high-definition cameras with a bitstream of 3M to 4M. The network structure is divided into the access, aggregation, and core layers. It is stored in the aggregation layer and each aggregation layer corresponds to 170 cameras.
Problems: How to choose products? What’s the difference between 100M and 1000M? What factors will affect the transmission of images in the network, and what factors are related to switches?
That 2 times of the sum of all port capacities*the number of ports should be less than the nominal backplane bandwidth can achieve full-duplex non-blocking wire-speed switching and prove that the switch has the conditions to maximize data switching performance.
For example, for a switch that can provide up to 48 Gigabit ports, its full configuration capacity should reach 48 × 1G × 2 = 96Gbps, which can ensure that it can provide non-blocking wire-speed packet switching when all ports are in full duplex.
2. Packet Forwarding Rate
Full configuration packet forwarding rate (Mbps) = the number of fully configured GE ports* 1.488Mpps + the number of fully configured 100M ports*0.1488Mpps
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 claimed packet forwarding rate is less than 35.71 Mpps (24 x 1.488Mpps = 35.71), then it is reasonable to assume that the switch is designed with a blocking architecture.
Generally, a switch with sufficient backplane bandwidth and packet forwarding rate is suitable.
Switches with relatively large backplanes and relatively low throughput should have problems with software efficiency/dedicated chip circuit design in addition to retaining the ability to upgrade and expand; switches with relatively small backplanes and relatively large throughput have relatively high overall performance.
The camera bitstream, usually the bitstream setting of the video transmission (including the encoding and decoding capabilities of the encoding sending and receiving equipment, etc.), affects the clarity, which is the performance of the front-end camera and has nothing to do with the network. It’s a misunderstanding that users think that the low clarity is caused by the network.
According to the above case, we can calculate:
3. Access Layer Switch
The main point 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 * the bitstream.
If a user is watching the video in real time, the bandwidth needs to be taken into account. The bandwidth occupied by each user to view a video is 4M. Assuming one person is watching, the bandwidth of the number of cameras * bitstream* (1+N) is required, that is, 24*4*(1+1)=128M.
4. Aggregation Layer Switch
The aggregation layer needs to process the 3-4M bitstream of 170 cameras at the same time, which means that the aggregation layer switch needs to support the simultaneous forwarding of more than 680M of switching capacity (170*4M=680M). Generally, the storage is connected to the aggregation, so the video recording is forwarded at wire speed.
However, considering the bandwidth of real-time viewing and monitoring. Each connection occupies 4M, so 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 support 10 users viewing each camera in real time at the same time.
5. Core Layer Switch
The core layer switch needs to consider the switching capacity and the link bandwidth of the aggregation. Because the storage is placed at 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 watching at the same time, each watching 16 channels of video, that is, the exchange capacity needs to be greater than 10*16*4=640M.
6. Keys to Selecting Switch
When selecting switches for video surveillance in a local area network, the selection of access layer and aggregation layer switches usually only needs to consider the factor of switching capacity, because users usually connect and obtain the video through core switches.
Besides, since the aggregation layer is not only responsible for monitoring the stored traffic, but also the pressure of viewing and calling monitoring in real time, it is very important to select the appropriate aggregation switches.