Powering PoE Switch From A PoE Switch: Is It Possible?

PoE (Power Over Ethernet) technology supports power and data transmission over the same Ethernet cable, which makes the cabling easier and greatly saves the space. Characterized by this advantage, PoE switch gains the popularity among many users. In practical application, we may meet some emergency, such as power failure. At this time, is powering PoE switch from a PoE switch possible? This article will discuss this topic.

Working Principe of PoE Switch

Before we come to the answer of powering PoE switch from a PoE switch, let’s learn about working principle of PoE switch. A whole PoE system consists of Powering Sourcing Equipment (PSE) and Power Device (PD). PoE switch is a type of PSE device. The PSE device not only powers Ethernet client devices, but also manage the entire Power over Ethernet process. While the PD device is PSE load which receives power, or we can call it PoE system client. The working principle pf PoE switch can be divided into five steps.

Detection: PoE switch outputs very small voltage on the port, until it detects that the PD equipment connected to the cable end supports the IEEE802.3af standard.

PD Classification: After detecting the PD, PoE switch may classify PD equipment, and assess the power loss of PD equipment.

Begin to Supply Power: In a configurable time (usually less than 15μs) start-up period, PoE switch begin to power PD equipment with low voltage, until it provides 48V DC power supply.

Power Supply: PoE switch provide stable and reliable 48V DC power for PD equipment to meet the power consumption which is less than 15.4W.

Power Off: If the PD equipment is disconnected from the network, the PoE switch will stop powering the PD equipment quickly, generally within 300-400ms, and repeat to detect whether the end of the cable is connected to the PD equipment.

Powering PoE Device From A PoE Switch

PoE switch is self-adaptive. When the PSE has the power supply requirement, the PD will output the voltage to the PSE. This means the switch can be powered by PoE while simultaneously providing power by PoE to other devices such as IP phones or wireless access points. This provides great flexibility because it means that the switch can be deployed without the constraints of an AC power outlet. As for powering PoE switch from a PoE switch, Universal PoE (UPOE) technology will be required and the following part will talk about UPOE. The following figure shows the evolution of PoE technology.

Evolution of PoE Standard

Powering PoE Switch From A PoE Switch with UPOE Technology

UPOE technology is a new innovation from Cisco Systems which happens to the industry’s first 60-watt Power over Ethernet technology. It can offer twice the power per port of the switch—providing both power and network access to a greater range of devices through a single standard Ethernet cable. This can surely help to lower the total cost of IT operations. By using UPOE technology, powering PoE switch from a PoE switch is possible. Here is an example to help you have a better understanding of this.

Most major networking vendors provide PoE Passthru, but they all require using higher powered sources. It physically would be impossible otherwise. If X is the power provided to the switch and Y is the power the switch uses, then Z is the power available for PoE devices. Then X – Y = Z. If you want Z to meet the PoE specification, then X has to be at least: Z + Y which means your input power needs to be UPOE.

Conclusion

As the enterprise workspace evolves with more and more end devices for communication, collaboration, security, and productivity, the need of PoE is also evolving to support newer end devices with increased power requirements. Regarded as upgrade of PoE, UPOE technology doubles the power delivered per port over PoE+ to 60 Watts which can extend resilient network power to a broad range of devices. What’s more, it realizes powering PoE switch from a PoE switch.

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