PoE switch introduction and function

A typical power-over-Ethernet system maintains Ethernet switch equipment in the wiring closet, and uses a power supply hub (Midspan HUB) to provide power to the LAN's twisted-pair cable. At the end of the twisted pair, this power is used to drive phones, wireless access points, cameras, and other devices. To avoid power outages, use a UPS.
It can supply power to PoE terminal devices such as wireless APs, webcams, VoIP phones, and PDAs via network cables. The transmission distance can reach 100m. The installation is simple and plug and play is possible. It is very suitable for wireless city, security monitoring and other industries.
PoE Switch Q&A:
1. Is PoE power supply stable?
From a technical point of view, PoE technology has developed for many years and is currently at a very mature stage. However, due to current cost pressures in the monitoring market, the quality of the PoE switches or cables used is too low, or the design of the solutions itself is unreasonable. As a result, the workload of PoE-powered project maintenance is particularly large. Therefore, PoE power supply is not universal among engineering firms. Stable point of view.
The network monitoring project is different from the ordinary network cabling, the data transmission volume is very large, the power is high, and it is required to work all-weather without interruption. The use of quality assured PoE equipment and wires is a guarantee for the stability of the entire system.
2. What are the advantages of PoE power supply solutions?
a. Simplify wiring and save labor costs
One network cable transmits data and power at the same time, and PoE eliminates the time required for expensive power and installation of power, saving cost and time.
b. Safe and convenient
The PoE power supply device only supplies power to the devices that need power supply. Only the devices that need power supply are connected, and the voltage of the Ethernet cable will exist. Therefore, the risk of leakage on the line is eliminated. Users can safely mix legacy devices and PoE devices on the network, which can coexist with existing Ethernet cables.
c, easy to remote management
Like data transmission, PoE can monitor and control the device by using Simple Network Management Protocol (SNMP). This feature can provide such functions as night shutdown, remote restart, and the like.
3. What are the risks or disadvantages of PoE power supply technology in engineering applications?
a. Insufficient power, the power receiving end does not move: The output power of the 802.3af standard (PoE) is less than 15.4 W, which is sufficient for a general IPC, but for a high-power front-end device such as a dome, the output power is not sufficient. To the request.
b. Risks are too concentrated: Generally, a PoE switch will power multiple front-end IPCs at the same time. Any failure of the POE power supply module of the switch will cause all cameras to fail to work. The risk is too concentrated.
c. Equipment and maintenance costs are high: Compared with other power supply methods, PoE power supply technology will increase the amount of post-sale maintenance work. From the standpoint of security and stability, the power supply alone has the best stability and security.
4. How to select a PoE switch?
a. Power supply needs to be supplied to devices with different power consumption: PoE switches adopt different standards and output power is different. For example: IEEE802.3af does not exceed 15.4 W. The maximum power consumption cannot exceed 12.95 W due to the loss of transmission wires. The equipment is powered. A PoE switch conforming to the IEEE802.3at standard can supply power to devices with a maximum power consumption of 25W or less.
b. How many devices can be powered at most: An important indicator of a PoE switch is the total power of a PoE. Under the IEEE802.3af standard, if the PoE power supply of a 24-port PoE switch reaches 370 W, then it can supply 24 ports (370/15.4=24), but if it is the maximum number of ports according to the IEEE802.3at standard The power supply is calculated at 30W, and at most 12 ports can be powered at the same time (370/30=12).
c. The number of interfaces required, whether it is with fiber ports, with or without network management, and rate (10/100/1000M).
5, PoE power supply safe transmission distance? What are the suggestions for the selection of network cable?
The safe transmission distance of POE power supply is 100 meters. It is recommended to use super five-category copper cable.
The issue of POE power supply network cables is only a problem in countries where counterfeit goods are rampant in China and is not a problem in many developed countries. The POE IEEE 802.3af standard requires the output power of the PSE output port to be 15.4W or 15.5W. The power received by the PD device after 100m transmission must be not less than 12.95W. The 802.3af typical current value is calculated as 350ma. The resistance of the 100m network cable must be It is (15.4-12.95W)/350ma = 7 ohms or (15.5-12.95)/350ma = 7.29 ohms.
The standard network cable meets this requirement naturally, and the IEEE 802.3af poe power supply standard itself is measured by a standard network cable. However, the problem of POE power supply network cables is only caused because many network cables in the market are non-standard network cables and are not produced in strict accordance with the requirements of standard network cables. The non-standard network cable materials in the market mainly include copper-clad steel, copper-clad aluminum, and copper-clad iron. These network cables have large resistance and are not suitable for POE power supply. The POE power supply must use an oxygen-free copper cable, which is a standard network cable.
PoE power supply technology has high requirements for wire rods. It is recommended that in monitoring projects, do not save money on wire rods and gain more.

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