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Analysis of common engineering problems in PoE switch

2018-05-24 10:11:25

PoE switches play an important role in wireless network coverage or wireless monitoring engineering. Although it is not so obvious as wireless AP, bridge and other devices, if there are problems in the actual application process, it will directly affect the entire wireless project.

In order to take some precautions into place before construction and reduce the maintenance of subsequent projects, the COMFAST of the wireless network coverage solution provider here lists several common engineering problems of PoE switches, and can help you to build and maintain wireless network projects better.

1. Power supply distance

It is known that the power supply distance of the PoE switch is generally 100 meters. In fact, the distance of the PoE power supply is determined by the data signal and the transmission distance, and the transmission distance of the data signal is determined by the network line.

1. Network requirements

The lower the impedance of the network line is, the farther the transmission distance is, so we should first guarantee the quality of the network line, purchase the authentic products, and recommend the use of super five types of net. The distance of the ordinary 5 types of line data signals is about 100 meters.

There are two kinds of PoE standard: IEEE802.af and IEEE802.3at standard. They are different in terms of over five kinds of wires, which are mainly reflected in the equivalent impedance. The equivalent impedance of IEEE802.3at should be less than 12.5 ohms and the IEEE802.3af should be less than 20 ohms if the 100 five super wires.

2, PoE standard

To ensure the transmission distance of the PoE switch, the output voltage of the PoE power supply is seen, and the 44-57V DC is as high as possible. The output voltage of the PoE switch port must conform to the IEEE802.3af/at standard.

2. Select the standard PoE switch

How to judge what is a fake PoE device

The fake PoE device only merges the DC power supply to the network cable through a PoE combiner. It can not be powered by standard PoE switches, otherwise the equipment will burn out. Therefore, in engineering applications, we should choose not only the standard PoE switches, but also the standard PoE terminals.

Security measures for standard PoE switches:

1, the power supply terminal (PSE) and the receiving end (PD) can dynamically perceive and adjust the supply voltage.

2, effective protection of the receiving end (usually IPC) is not burned by electric shock (other aspects include short circuit, surge protection, etc.).

3, intelligent detection terminal supports PoE, and will not supply power when accessing non PoE terminals.

Non standard PoE switches usually save cost and do not have the above security measures.

3, switch cascading problem

The number of switches cascaded involves the calculation of bandwidth. A simple example:

If the 100M network port switch is cascaded to the center, the effective bandwidth is 45Mbps (bandwidth utilization 45%). If each switch connects the common 15Mbps monitoring equipment, that is, the single switch bandwidth 15M, then the 45/15 3, and the cascade 3 switches.

Why is the bandwidth utilization equal to about 45%?

The actual Ethernet IP packet header accounts for about 25% of the total flow rate, and the actual utilization link bandwidth is 75%. In actual applications, the reserved bandwidth is considered to be 30%, so the insurance estimation bandwidth utilization is 45%.

4, choose the PoE switch according to the power of the device.

How big is the power of the device, and then choose the PoE switch with high power. If the power of your device is below 15W, then choose the PoE switch that supports the 802.3af standard. If the power is greater than 15W, it is necessary to select the 802.3at standard high-power switch, otherwise it will not move. Of course, your device is supported by PoE. If you do not support PoE, you need to prepare a PoE separator.

More PoE switch related problems, you can find professional wireless coverage solution provider Shenzhen Sihai Zhonglian (brand COMFAST) consultation.