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What is PoE -Part 2

PoE, abbreviation of Power over Ethernet, is a technology that allows network cable(Ethernet cable) to transmit electrical power for PoE-enable devices. It is a cost-saving solution for you to deploy IP device conveniently with existing CAT-5 Ethernet infrastructure without the need to make any modifications. While it has developed over 10 years, people still have doubts and misconception to PoE. This article intend to explain PoE in depth but simply.

PoE has compatibility issue? Actually it is not. In the early time, PoE confronted with compatibility problem because there is no standard for the power and voltage. Therefore, different PoE products from different vendors can not work together. However, this issue was settle in 2003 when PoE is defined as IEEE 802.3af standard by the Institute of Electrical and Electronic Engineers (IEEE), which is the largest technical professional organization in the world. Nowadays, most of PoE devices on the market is complied with IEEE 802.3af/at standards, even from different vendors.

PoE Standard

802.3af PoE Standard: This standard is able to support 15.44 watts of power, but in practice, powered devices (PDs) reliably receive 12.95 watts due to power losses through the circuit.

802.3at PoE Standard: Also known as PoE+, this standard supports 30 watts of power, but as with the 802.3af standard, power losses lower the amount supplied to 25.5 watts.

802.3bt or PoE++ Standard: It is a higher powered PoE standard, also called the next generation standard that may provide up to 90 watts by using 4 pairs of balanced twisted-pair cabling.

Active PoE vs. Passive PoE

If the PoE device is compatible with PoE IEEE802.3af/at/bt standard with a fixed 48V power voltage, it can be considered as active PoE. Active PoE devices will auto-detect the power requirement of powered devices(PDs) and power can be transmitted accurately, avoiding over-powering or under-supplying issue. While passive PoE is on the contrary, it means any device using PoE that is not IEEE 802.3 standard. And it supply power to powered devices without negotiation, which easily damages the PoE devices or shortens their life. Therefore, according to different IEEE 802 standards, there are 4 class types to categorize power requirement for powered devices.

PoE Class Types

Classification ensures that powered devices receive the appropriate level of power. This also allow the PSE to allocate the left unused power to other PDs. The below table will present the range of power allocated with different class types for 802.3 standard powered devices(PDs).

Mode A vs. Mode B

The power supply of PoE devices is divided into two methods, namely Mode A and Mode B. Ethernet cable is 4 pair twist copper cable with 8 pinouts.

Mode A: It is also known as Alternative A, which refers using 2 pairs data pinouts 1-2 and 3-6 to transmit or receive power and data, and the other two pairs 4-5 and 7-8 pinouts are unused. Mode A devices are sometimes referred to as end-span units.

Mode B:  When devices operate in Mode B, it means all data pairs are used. Mode B sends data using pinouts 1-2 and 3-6.  Power is sent using data pin pairs 4-5 and 7-8. Mode B devices are also referred to as midspan devices.

What are the advantages of Power over Ethernet?

  • Money saving – PoE technology requires few electricity technical knowledge, you can finish the installation following instruction, saving the cost for hiring professional electrical installers. What’s more, there’s no need to build extra wire cabling as power and data are transmitted over single Ethernet.
  • Flexibility- PoE is popularly applied in the places where hard to find power supply(AC outlet) or reach easily, such as ceiling, outdoor deployment, industrial environment.
  • Standardization – Majority of PoE devices are complied with IEEE 802.3af/at/bt standard, which implies most of powered devices that you own will not confront compatibility problem, proving convenience when choosing PoE devices.
  • Easy to use – connect power sourcing equipment (PSE) to PDs with twisted-pair Ethernet cable, such as IP cameras, VoIP phones, or WAPs, if you have existing ethernet switch or require high power, adding PoE injector can help to deal with power supply for powered devices, such as IoT applications, pan-tilt-zoom (PTZ) IP cameras, Point of Sales (POS) etc.
  • Scalability – PoE devices are designed plug and play, you can add new equipments fast without expensive and inconvenient new powerline installation.
  • Safety – PoE devices work in low power voltage so that it is safe enough to reduce electrical accident for the network system.

PoE technology and IoT application influent each other. You are supposed to embrace them with expectation. Want to know more about PoE solution, contact us to get suitable PoE devices for building your wired cabling system.

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