1. Main considerations for PoE switch selection
1. Select a standard PoE switch
In the previous PoE column, we mentioned that the standard PoE power supply switch can automatically detect whether the terminal in the network is a PD device that supports PoE power supply.
The non-standard PoE product is a strong power supply type network cable power supply device, which supplies power as soon as it is powered on. Therefore, first make sure that the switch you buy is a standard PoE switch, so as not to burn the front-end camera.
2. Equipment power
Select a PoE switch according to the device power. If the power of your surveillance camera is less than 15W, you can choose a PoE switch that supports the 802.3af standard; if the power of the device is greater than 15W, then you need to choose a PoE switch of the 802.3at standard; if the power of the camera exceeds 60W, you need to choose 802.3 BT standard high-power switch, otherwise the power is insufficient, and the front-end equipment cannot be brought.
3. Number of ports
At present, there are mainly 8, 12, 16, and 24 ports on the PoE switch on the market. How to choose it depends on the number and power of front-end connected cameras to calculate the total power number. The number of ports with different power can be allocated and combined according to the total power supply of the switch, and 10% of the network ports are reserved. Be careful to choose a PoE device whose output power is greater than the total power of the device.
In addition to meeting the power requirements, the port should also meet the communication distance, especially the ultra-long distance (such as more than 100 meters) requirements. And it has the functions of lightning protection, electrostatic protection, anti-interference, information security protection, prevention of virus spread and network attacks.
Selection and configuration of PoE switches
PoE switches with different numbers of ports
4. Port bandwidth
Port bandwidth is the basic technical indicator of the switch, reflecting the network connection performance of the switch. Switches mainly have the following bandwidths: 10Mbit/s, 100Mbit/s, 1000Mbit/s, 10Gbit/s, etc. When choosing a PoE switch, it is necessary to first estimate the traffic flow of several cameras. When calculating, there should be a margin. For example, a 1000M switch cannot be fully estimated. Generally, the utilization rate is about 60%, which is about 600M. .
Look at a single stream according to the network camera you use, and then estimate how many cameras can be connected to a switch.
For example, a single code stream of a 1.3 million-pixel 960P camera is usually 4M,
If you use a 100M switch, you can connect 15 sets (15×4=60M);
With a Gigabit switch, 150 units (150×4=600M) can be connected.
A 2-megapixel 1080P camera usually has a single stream of 8M.
With 100M switch, you can connect 7 sets (7×8=56M);
With a gigabit switch, 75 sets (75×8=600M) can be connected.
5. Backplane bandwidth
Backplane bandwidth refers to the maximum amount of data that can be handled between the switch interface processor or interface card and the data bus.
The backplane bandwidth determines the data processing capability of the switch. The higher the backplane bandwidth, the stronger the ability to process data and the faster the data exchange speed; otherwise, the slower the data exchange speed. The calculation formula of the backplane bandwidth is as follows: Backplane bandwidth = number of ports × port rate × 2.
Calculation example: If a switch has 24 ports, and the speed of each port is gigabit, then the backplane bandwidth=24*1000*2/1000=48Gbps.
6. Packet forwarding rate
The data in the network is composed of data packets, and the processing of each data packet consumes resources. Forwarding rate (also called throughput) refers to the number of data packets that pass through per unit of time without packet loss. If the throughput is too small, it will become a network bottleneck and negatively affect the transmission efficiency of the entire network.
The formula for the packet forwarding rate is as follows: Throughput (Mpps) = Number of 10 Gigabit ports × 14.88 Mpps + Number of Gigabit ports × 1.488 Mpps + Number of 100 Gigabit ports × 0.1488 Mpps.
If the calculated throughput is less than the throughput of the switch, wire-speed switching can be achieved, that is, the switching rate reaches the data transmission speed on the transmission line, thereby eliminating the switching bottleneck to the greatest extent.
Post time: Jun-09-2022