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Power Over Ethernet full report
Post: #1

Power Over Ethernet


¢ Power over Ethernet is a mechanism for supplying power to network devices over the same cabling used to carry network traffic. PoE allows devices that require power, called Powered Devices (PDs),such as IP telephones, wireless LAN Access Points, and network cameras to receive power in addition to data, over existing infrastructure without needing to upgrade it.
¢ This feature can simplify network installation and maintenance by using the switch as a central power source for other network devices

Presented By
Allied Telesyn


The advantage of PoE

Some of the advantages of PoE include:
¢ A single cable between switch and Powered Device (PD)
¢ No separate power installation/ connection needed for PD's
¢ Simplified installation and space saving
¢ Device placement is not limited to nearby power sources
¢ PD's can be easily moved to wherever there is LAN cabling
¢ Safety - no mains voltages anywhere
¢ A UPS can guarantee power to devices even during mains failure
¢ Devices can be shut down or reset remotely
¢ Little configuration or management required

PoE Devices

¢ VoIP phones
¢ Wireless access points (for example AT-WA75xx)
¢ Ethernet hubs
¢ Digital clocks
¢ Webcams
¢ Security cameras
¢ Intercoms
¢ Building access systems
¢ Even a network electric guitar
¢ Plus others¦

PoE standard

¢ The PoE IEEE 802.3af standard was formally approved by the IEEE Standards Board in June 2003 and is an amendment to the existing IEEE 802.3 standards.
¢ Power Sourcing Equipment (PSE) “ power source can be an Ethernet switch
¢ Power Device (PD)

How PoE works

¢ PoE requires little configuration or management.
¢ The PSE automatically determines whether a device connected to a port is a powered device or not, and can determine the power class of the device.
¢ The PSE can supply up to 15.4 watts of power (at 48 Volts) to the device, while at the same time providing standard Ethernet network functionality.

Power Device (PD) discovery

¢ The first step for PSE equipment (an Ethernet switch for example) is to ascertain whether a device plugged into a port is a valid Powered Device (PD).
¢ The IEEE 802.3af-2003 standard for device detection involves applying a DC voltage between the transmit and receive wire pairs, and measuring the received current.
¢ A PSE will expect to see approximately 25K Ohm resistance and 150nF capacitance between the pairs for the device to be considered a valid PD.
¢ A range around these values is specified in the IEEE 802.3ad standard.
¢ The PSE will check for the presence of PD's on connected ports at regular intervals, so power is removed when a PD is no longer connected.

Power classes

¢ Once a PD is discovered, a PSE may optionally perform PD classification by applying a DC voltage and current to the port. If the PD supports optional power classification it will apply a load to the line to indicate to the PSE the classification the device requires.
¢ Allocated power is subtracted from total power budget
¢ Any unclassified PD is considered to be a class 0 device.
¢ The IEEE 802.3af standard supports delivery of up to 15.4 watts per port that may be used to deliver power to PoE devices.
¢ The maximum power consumed by a PD, as specified by the standard, is 12.95 watts.
¢ The system provides the 'extra' power (up to 15.4 watts) to compensate for line loss.

Power through the cable

¢ An Ethernet cable (CAT5) has four twisted pairs, but only two of these are used for data transfer.
¢ The spare pairs are used. In this case the unused pairs are used to transfer the power.
¢ The data pairs are used. Since Ethernet pairs are transformer coupled at each end, it is possible to apply DC power to the centre tap of the isolation transformer without upsetting the data transfer.
¢ The IEEE 802.3af standard does not allow both sets of wires to be used
¢ Different vendors PSE equipment may use one or other of the methods to supply power depending on PoE implementation
¢ So the PSE applies power to either the spare or data wires.
¢ The Powered
¢ Device (PD) must be able to accept power from both options.
¢ The voltage supplied is nominally 48V, and a maximum of 12.95W of power is available at the Powered Device.
¢ An isolated DC-DC converter transforms the 48V to a lower voltage more suitable for the electronics in the Powered Device.

Power Capacity

¢ Ther is enough power for the switch itself, and has 400 watts available for PoE provision.
¢ The maximum possible power requirement (24 ports * 15.4W = 370 watts) falls below the maximum amount of power available (400 watts).
¢ You can reduce the amount of power a port can source, from the maximum of 15.4 W, using the command:
set poe [{port=port-list|ALL}] [priority=low|high|critical] [powerlimit=value]

Power threshold

¢ The switch sends a Simple Network Management Protocol (SNMP) trap to your management workstation and enters an event in the event log whenever the total power requirements of the powered devices exceed the specified percentage of the total maximum power available on the switch. At the default setting of 95%, the switch sends an SNMP trap when the PoE devices require more than 95% of the maximum available power on the switch.
set poe threshold=value

Powered Device (PD) detection

¢ The Allied Telesyn implementation of PoE offers two methods of PD detection.
¢ The default is to use the IEEE 802.3af standard resistance and capacitance measurements as described earlier.
¢ Thesecond option is to support legacy PD's that were designed before the IEEE standard was finalised.This involves measuring for a large capacitance value to confirm the presence of a PD.

¢ In legacy mode, the IEEE method will be tried first and failing the discovery of a valid PD the legacy capacitance measurement will be tried.
¢ PD detection is carried out in real-time by the PSE controller on each switch port to detect and monitor the presence of any powered devices. Power is not supplied to an specific port until a valid PD is detected. A switch port which has a PD unplugged, will cease to have power supplied.

Software monitoring

¢ The 'show switch port=x' command has some additional parameters added, specifying whether PoE is enabled on the port and any power limit and priority that have been set.
¢ The 'show poe' command details power threshold set, a power usage percentage, and power consumed by each switch port.
¢ The 'show poe port=x' command details the PoE information for a specified port, including power limit, power consumed, power class¦
Post: #2

PoE Explained
Since its standardization in 2003, Power over Ethernet (PoE) has found widespread application in markets such as VoIP telephony, wireless LANs, IP video security and access control. As discussed in Veracity's earlier article, Power Without the Struggle, its benefits as a power delivery method include drastically lower installation and maintenance costs, and its technology offers a supply that is reliable, safe, efficient and robust, while being as simple as possible to install. PoE gives network installers control over the power distribution to their equipment, however for many this is not their forté: while the concepts behind PoE are straightforward in absolute terms compared to the complexities of other IT technology, the fundamentals of electrical power and its delivery are new territory to a significant proportion of users. This white paper, therefore, intends not only to serve as a reference to those technical features of PoE that are relevant to users of network equipment, but also to provide further explanation of the basic principles behind the technology, so that these features may be understood well enough to enable the effective design, installation and troubleshooting of PoE-enabled networks.
Presented By
Veracity UK Ltd
6 Barns Street

Post: #3




Power over Ethernet is a mechanism for supplying power to network devices over the same cabling used to carry network traffic.
PoE allows devices that require power, called Powered Devices (PDs),such as IP telephones, wireless LAN Access Points, and network cameras to receive power in addition to data, over existing infrastructure without needing to upgrade it.

This feature can simplify network installation and maintenance by using the switch as a central power source for other network devices.

1. Cost Saving:
PoE saves time and money by avoiding the need for separate installation of Data and Power infrastructure.
2. Simplicity
Power is fully integrated with Ethernet infrastructure, so access to rough places for power deployment become simpler.
3. Reliability
As a central UPS joins in, reliability rises. Moreover, the need for a local backup for each AC outlet is avoided
4. Control
Network management infrastructure provides control and monitor of the Powered Devices; Shutdown & reset on remote.
5. Security
Shutting down unnecessary PDs when no one is at office ensures better business security.

IP telephony
web cameras
PDA, notebooks
embedded PC, Ethernet devices and their periphery
remote sensors
industrial or in-house automation
cash desks
security and monitor systems
supplying of line converters

Post: #4
please give full report
Post: #5
send me full report or documentation on power over ethernet to this mail
Post: #6
sen me documentation on power over ethernet

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