What is POE? when we can use POE switch and why we required POE switch?
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PoE = Power over Ethernet (used to power devices like IP Phones and Wireless Access Points over existing copper without the need for Power Cords located at the end device)
Here is the Cisco description;
Power over Ethernet (PoE) is the ability for the LAN switching infrastructure to provide power over a copper Ethernet cable to an endpoint or powered device.
This capability was developed and first delivered by Cisco in 2000 in order to support the emerging IP Telephony deployments. IP telephones, such as desktop PBX phones, need power for their operation, and PoE enables scalable and manageable power delivery and simplifies deployments of IP Telephony.
While IP telephones and wireless access points (APs) are the most intuitive uses for PoE, the advent of the 802.3af standardization of PoE opens the door to a new generation of network-attached devices, such as video cameras, point-of-sale devices, security access control devices (card scanners), building automation and industrial automation.
PoE promises to create a new world of networked appliances as it provides power and data connectivity over existing Ethernet cables.
This document answers some of the most frequently asked questions about Cisco IP phone power requirements.
Q. What is Power over Ethernet?
A. Power over Ethernet (PoE) is the ability to deliver 48 VDC of power over the same copper cable as Ethernet. Two primary elements are required in order to implement PoE. They are:
power sourcing equipment (PSE)-the LAN switch or source power delivered over Ethernet
the powered device (PD)-the end device that accepts and uses power from the Ethernet cable for its operation
Here is some related info (note that all competitors now use 802.3af);
This describes the differences between the older Cisco Inline Power (proprietary) and the Standards based 802.3af;
Cisco Inline Power and IEEE 802.3af
Cisco launched Cisco Inline Power in March 2000 and has shipped more than 16 million inline power capable ports on the Catalyst switches. This innovation was quickly recognized within the industry and the IEEE started work to standardize Power over Ethernet implementations such that multi-vendor interoperability was enabled. With the ratification of IEEE802.3af, as with other Cisco innovations, Cisco will support both IEEE 802.3af and prestandard Power over Ethernet concurrently. Cisco has also extended prestandard power management extensions using Cisco Discovery Protocol negotiation to Cisco IEEE 802.3af compliant devices to further optimize PSE power management.
Applying Power over Ethernet requires that the device type be resolved to ensure that power is not applied to nonpower capable devices. To prevent unfortunate mishaps and to reduce the burden of network administration, Cisco and the IEEE devised mechanisms whereby the switch is able to determine whether a powered device or a nonpowered device is attached to a port. However, the phone detection mechanisms used by the Cisco prestandard Power over Ethernet implementation and IEEE802.3af are different in that the Cisco prestandard Power over Ethernet implementation uses AC powered device detection and IEEE 802.3af uses DC powered device detection. DC detection differs from AC detection in that AC detection transmits a low frequency AC signal and expects the same signal to be received back on the receive pair. DC detect applies a DC Current and detects the presence of a powered device by measuring the load applied by the powered device. It should be noted that Cisco IEEE 802.3af compliant devices support prestandard and IEE 802.3af detection mechanisms.
Using a Cisco inline power capable switch or Power Sourcing Equipment (PSE), the switch port will send discovery signals on active and inactive Ethernet ports to detect whether a powered device is present or not.
continued on next post......