On a previous post, we have already discussed about PoE, which stands for power over Ethernet. It describes various standards and ad-hoc systems allowing passing electric power along with the bandwidth data through twisted pair cables. Two of these techniques are standardized by IEEE 802.3 starting from the year 2003. These standards (802.3 af vs 802.3 at) are known as below:
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As the main title implies, this post is dedicated for comparing major technical and performance difference between these two “Power Over Ethernet (PoE) Standards.” These standards define specifications of the devices being powered using PoE technique. They define specifications of power sourcing equipment or PSE as well. PSE devices are simply used for delivering power / electric energy on Ethernet cable, while PSE is the PD (powered device) is the device consuming the energy delivered by PSE. (i.e., IP compliant mobile phones, IP compliant cameras, wireless APs, etc.)
Also Read: Difference between POE Switch and InjectorRelated: List of Best POE Switches
Also Read: Difference between POE Switch and Injector
Related: List of Best POE Switches
Now let’s move to the primary topic of this post. Before jumping deep into details, following is a simple comparison of features offered by these PoE and PoE+ standards. Have a look below:
Table of Contents
Before jumping deep in technical details, here are general features of IEEE 802.3af and 802.3at, which also roughly describe their differences:
Related: Best Powerline Ethernet Adapter
Following table describes the differences with further details, you may want to have a look before we discuss other technical stuff:
Cat 3 Cable
Cat 5 Cable
0.1 W step negotiation by LLDP
(i.e., dual pair)
Category 5 Cable (Cat 5)
Mode B (Midspan)
As the tables above show, IEEE 802.3af PoE standard delivers up to 15.4 W DC power on each port while delivering minimum 44 V DC and 350ma. With this standard, some power gets dissipated in the cable, and thus only 12.95W is available for the powered device. 802.3at PoE standard is an updated version of the former standard. It is also referred to as PoE+ or PoE plus. It promises to deliver 25.5 W of power to devices with Type 2 support.
Powered devices are prohibited from utilizing all four pairs for power in this standard. Note that both of these PoE and PoE+ standards are incorporated under IEEE 802.3 2012. Generally, power devices supporting IEEE 802.3at PoE+ standard are referred to as PoE Type 2 devices. On the other hand, devices compatible with only IEEE 802.3af PoE standard are known as PoE Type 1 devices.
(Voltage / V)
To improve the performance of 802.3 at, layer two communication signals are used by PSE. IEEE 802.3at devices are capable of utilizing Class 4 current as they possess valid class 2 and mark two currents for the power-up stages. If an 802.3af compliant device presents class 4 current, it is treated as a Class 0 devices since its non-compliant.
Having all these differences, here are some common advantages of these protocols or standards offer in networking:
That’s it for the difference between 802.3af PoE and 802.3at PoE+ protocols. We hope this post helps you to understand the major differences between these two protocols. There are even new updates protocols available, we will discuss about them in another post. If there is any query, suggestion or doubt on your mind, feel free to contact us directly or comment down below. We are always looking forward to hearing from our readers. Make sure to subscribe for regular tech updates, See you until next post!
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