PoE (Power over Ethernet) technology allows PSE (Power Sourcing Equipment, such as a PoE switch) to use Ethernet cables to deliver both power and data simultaneously to PD (Powered Device, like IP cameras and VoIP phones), which can simplify cabling installation and save cost. Different PoE standards like IEEE802.3af, 802.3at and 802.3bt are released by IEEE (Institute of Electrical and Electronic Engineers) to regulate the amount of power delivered to those PDs. Then how much do you know about those PoE standards? How many PDs can be connected to a PSE based on different PoE wattages? Here offers a detailed explanation.
At present, PoE standard has three types: IEEE 802.3af, IEEE 802.3at and IEEE 802.3bt. Those PoE standards define the minimum power that PSE can source and the maximum power that the PD will expect to receive.
IEEE 802.3af is also known as standard PoE with supply voltage of 44-57V, and supply current of 10-350mA. In this standard, the maximum power output of a port is limited to 15.4W. However, some power will be lost on the Ethernet cable during the transmission. Thus, the minimum guaranteed power available at the PD is 12.95 watts per port. It can support VoIP phones, sensors and so on.
The updated IEEE 802.3at standard also named PoE+, which is backward-compatible with standard PoE. The supply voltage of PoE+ ranges from 50V to 57V, and the supply current can be 10-600mA. It provides up to 30W of power on each port of a PSE. Due to power loss, the minimum output power assured on each port is 25W. This type can support devices that require more power like LCD displays, biometric sensors and tablets.
IEEE 802.3bt is the latest PoE standard that defines two types of powering/wattage standards - Type 3 and Type 4 in the table above. They will increase the maximum PoE power by delivering more power through two or more pairs of Ethernet cables. In Type 3 and Type 4 modes, PSEs will identify the PDs and set the power accordingly to the maximum PD power, resulting in a better power-delivery system.
Type 3 is also known as PoE++, which can carry up to 60W for each PoE port (minimum power ensured on each PD port is 51W) over a single RJ45 cable to power devices like video conferencing system components.
Type 4 is named higher-power PoE. It can supply maximum power output of 100W on each PoE port (minimum power ensured on each PD port is 71W), which is suitable for devices like laptops or TVs, etc. Both the two modes of IEEE 802.3bt are backward compatible with 802.3af and 802.3at. The following table concludes the specifications of the PoE standards. The following table concludes the specifications of the PoE standards.
|Type||Standard||PD Min. Power Per Port||PSE Max. Power Per Port||Cable Category||Power Over Pairs||Released Time|
|Type 1||IEEE 802.3af||12.95W||15.4W||Cat5e||2 pairs||2003|
|Type 2||IEEE 802.3at||25W||30W||Cat5e||2 pairs||2009|
|Type 3||IEEE 802.3bt||51-60W||60W||Cat5e||2 pairs class0-4, 4 pairs class5-6||2018|
|Type 4||IEEE 802.3bt||71-90W||100W||Cat5e||4 pairs class7-8||2018|
IEEE 802.3af and 802.3at are the most common PoE standards that a wide majority of PoE devices can support. IEEE 802.3bt has been newly released, which is not in large-scale use. Only a few vendors’ products support this standard, such as FS S5860-24XB-U, which is a PoE++ switch that supports auto-sensing IEEE 802.3af/at/bt PoE standard. Therefore, we just discuss PoE wattage of IEEE 802.3af and 802.3at here.
As described above, standard PoE can supply maximum power output of 15.4W, while PoE+ is 30W. When a plan calls for multiple devices to be connected to one PoE/PoE+ switch, it’s necessary to ensure the total wattage required by the devices does not exceed the maximum wattage of the switch. Here takes FS S3400-24T4FP PoE/PoE+ switch as an example. It’s a managed switch with 24 RJ45 ports and 4 SFP ports. It complies with IEEE 802.3af/at, the total power budget is 370W. This means the 24-port switch provides the availability of PoE and PoE+ power. Therefore, this switch can simultaneously connect 24 (15.4W×24=369.6＜370W) devices with PoE standard. And it can support 12 (30W×12=360W＜370W) devices with PoE+ standard.
Figure 2: Applications of FS PoE+ switches.
Usually, if a network switch supports both PoE and PoE+ standards, it can automatically detect whether the connected device is compatible with PoE or PoE+, and supply the suitable power to the device. For example, if we connect a PoE-enabled device with 5W power to the S3400-24T4FP PoE/PoE+ switch, then the switch will provide 5W power to the device. If we connect the switch with a PoE-enabled device that requires 20W power, then the switch will supply it with 20W power. And if we connect a device without PoE ability to the PoE switch, the switch will only deliver data to the device.
FS now has PoE/PoE+ switches that follow the PoE standard for higher security and better ability. They are available in 8/16/24/48 ports options. These switches support layer 2+ switching features like VLAN. They also offer advanced management like WEB, CLI, TELNET, SNMP. FS PoE/PoE+ switches can power any 802.3af or 802.3at device of the market, making them flexible and secure. The following table lists the specifications of 4 FS PoE/PoE+ switches.
|PoE Standard||Model||Port||Switch Capacity||Power Budget||Forwarding Rate||Fans|
|IEEE 802.3af/at||S3260-8T2FP||8x RJ45 | 2x SFP||20 Gbps||240W||15 Mpps||With Fans|
|IEEE 802.3af/at||S3410-24TS-P||24x RJ45 | 2x SFP+, 2x RJ45/SFP||88 Gbps||370W||66 Mpps||With Fans|
|IEEE 802.3af/at||S5500-48T8SP||48x RJ45 | 8x 10G SFP+||256 Gbps||370W||192 Mpps||With Fans|
|S5860-24XB-U||24x Base-T | 4x SFP+, 4x SFP28||
||370W||565 Mpps||With Fans|
PoE standards specifies the maximum power output of a PSE, helping protect PoE-enabled devices from high-voltage damage. In addition, PoE technology can make the cabling installation easier and save your costs. It’s especially suitable for IP monitoring and remote monitoring applications, such as a PoE electronic billboard, or a PoE electronic display.