Why Power over Ethernet?

The LAN, to date, has been utilized for Data Flow only. Central equipment; Hubs, Routers and Switches are plugged into the mains, as is the User Terminal. An independent infrastructure is the telephone system, in which the end terminal does not need to be connected to the mains.

Recent trends in telecommunications are attempting to marry traditional telephony with today's networks. IP Telephony converges voice and data, opening a new world of opportunities and features. This serves today's telephony well, until faced with a power failure or lack of a mains socket, presenting reliability issues. PowerDsine addresses this issue by injecting power over the spare pairs of the TIA/EIA-588 Category 5 and above cable. This in itself solves the IP telephone power problem and opens doors to new applications for the LAN.

PowerDsine Power over Ethernet technology converges power, voice and data by delivering an electrical supply and data communications over a single standard LAN cable. This eliminates the need for connecting each Ethernet terminal to both an electrical socket and a data outlet, thereby reducing a corporation's installation and maintenance costs. It also enhances system reliability by maintaining telephony service during power interruptions. In addition, the technology's ability to use a single uninterrupted power supply (UPS) for backup operations within the network enables enterprises to realize their full LAN potential and further reduce installation costs.

What is Power over Ethernet?

A Power over Ethernet system comprises of an Ethernet switch and a Power-Hub or a Power over Ethernet enabled Ethernet switch, which serves as the power source, and a number of Power enabled DTE, which are the loads. The system is a Star topology, where each load is connected with a dedicated connection to the centralized Power-Hub.

The Power-Hub is connected in series to an Ethernet switch/Hub (cascaded) where the Power-Hub inputs are connected to the switch outputs, and the Power-Hub outputs are connected to the patch panel. Power is carried over the spare twisted pairs (pins 7 & 8) and (pins 4 & 5) in an ordinary Category 5 and above cable with negligible degradation of data communication.

What does PowerDsine provide?

A Power over Ethernet Hub, Power-Hub, resembles a patch panel and has 6, 12 or 24 channels, injects the power to the LAN cables. The Power-Hub integrates internal power modules, each module contains a RJ-45 input Data connector and a RJ-45 output connector for the combined Data and Power. A passive module's input to output 10/100BaseT circuitry guaranties bi-directional data flow is maintained, regardless of the module's power status.

The PowerDsine SPEAR, is an internal sophisticated power control and monitoring circuit. It is implemented on each of the power channels and activates the power only when a Power over Ethernet ready Ethernet terminal is present. This prevents the injection of power, and damage of devices such as ordinary NICs, which do not expect power on their Ethernet connection. The SPEAR also provides protection against channel overload and short circuit, reversed polarity caused by a faulty connection or a crossed cable and the connection of two feeding channels to each other.

Each PowerDsine Power-Hub provides remote power feeding for the 6, 12 or 24 terminals from a centralized universal AC input or an external DC power supply. The external 24/48Vdc input may be used to provide optional redundant power feeding. The -24V Power-Hub is designed to ensure at least 8W per output (measured at the channel output port) in order to deliver maximum of 5.6W at the device terminals (after reducing maximum of 100m cabling power drop). The -48V Power-Hub is designed to provide up to 13W at the device terminals. A single port Hub is also available either with -24Vdc or -48Vdc outputs.

How is Legacy Equipment Protected?

For a terminal to receive power on the Ethernet line it must be designed as such. Special detection routines are performed on each port before power is injected, in order to confirm that the terminal is ready. If equipment is not "Power Enabled" the Power-Hub will not supply power to that port. Equipment that is to be powered over the Ethernet is designed to be compatible with a particular Power-Hub and recognizable by it.

PowerDsine Power over Ethernet Application Notes can be downloaded from the PowerDsine Web site. The documents detail how the terminal recognition is performed, and how to build "Power Enabled" equipment.

PowerDsine was a founding member of the standards committee. More details can be found at the site http://grouper.ieee.org/groups/802/3/af/index.html

If a device is incompatible with a Power-Midspan, an external splitter can be installed. The splitter separates the DC voltage and the Ethernet data signal into two separate wires, terminating at a power port and a RJ-45 jack.

How is the Terminal Interrogation Performed?

A PowerDsine Power-Hub interrogates the terminal by putting a constant voltage, current limited source on the wire pairs that are to be powered. A particular capacitive detection circuit is usually designed into equipment that is "Power Enabled". This circuitry returns the voltage in a certain manner that is analyzed by the Power-Hub microprocessor. Only if there is a recognized characteristic, will the Power-Hub inject Power down the line to the Terminal. Most Terminal units can be powered with a PowerDsine Power-Hub, even if they have not been specifically designed Power Enabled. As a minimum an external splitter can be utilized. The user should be in contact with PowerDsine in order to certify the Terminal Power Enabled.

The interrogation process takes very short period of time, depending on the identification characteristics of the Terminal connected. It is repeated at regular intervals on each un-powered port. If a terminal is removed the channel will power down.

PowerDsine advocates the use of the spare wires in an ordinary Cat 5 cable, pairs 4,5 and 7,8. So only these lines are interrogated.

What could be expected if a voltage will be on the 1,2 & 3,6 pairs?

The benefit of the Power over Ethernet is the detection routine, this has high priority in the IEEE standards. Before power is injected to a terminal, the terminal will be 'interrogated' to see if it is "Power Enabled". This Interrogation will be performed on the same lines as the power is due to be supplied.

Therefore if no 'identification' is on pins 1,2,3,6 then no power will be supplied. A terminal will have to be designed correctly in order to receive power on those pins.

Isolation and Safety for PowerDsine Power over Ethernet Power-Hubs:

What is the AC/DC isolation in the power Hub?

The power supply of the Power-Hub is rated with 3KV insulation between its input and output.

Why should Isolation be used in the IP telephones?

The Power-Hub channels are not isolated from each other. [This is not required and would become very expensive]. This means that two terminals that are connected to ground, could be at different potentials and cause damage to the Power-Hub via Ground Loops. If a terminal does not have any external connections, which could be connected to ground, then it does not need to be isolated. i.e. the casing (if plastic) is acceptable isolation.

Regarding safety - which severance is met?

The Power-Hub is designed to Double Isolation Class 2. The unit is designed to meet UL, CSA and TUV

Is the output voltage supply floating or earthed to ground?

The output voltage supply is floating.

Are the Power-Hubs ready for 1KV surge (2msec to 5msec)?

Yes, the Power-Hubs have been tested with transients on the input and output connections.

How many telephone sets can a Ring Generator drive?

PowerDsine Ring Generators are defined for both maximum wattage and maximum REN. To find these maximum ratings, please refer to the product's specifications. Short form specifications are also available in the PowerDsine Ring Generators Selection Guide. A Ring Generators' ability to ring multiple telephone sets is a function of the amount of power that can be continuously dissipated inside the Ring Generator without causing damage to it. This is effected by many parameters, including the Ring Generator's efficiency, ambient temperature, the loads' power factor and the operating duration.

When our specifications define maximum REN, unless otherwise specified, we refer to a standard North American REN. A standard 1 North American REN represents the ringer loading effect of 6930W in series to an 8mF capacitor. A 5 North American REN represents the ringer loading effect of 1926Ohm in series to a 40mF capacitor.

A SONY SPP-X90 cordless telephone, for example is rated 0.3B REN. This means that the PowerDsine PCR-SIN03A Ring Generator, for example, which is rated 5REN maximum, can continuously drive 10 SONY SPP-X90 telephone sets.

What is the Ringer Equivalent Number (REN)?

Ringer Equivalency Number (REN) is a number determined in accordance with the U.S. Code of Federal Regulations, Title 47, part 68, which represents the ringer loading effect on a line. A REN of 1 represents the loading effect of a single traditional telephone set ringing circuit. Modern telephone sets may have a REN lower than 1. Depending on the applicable Telecom standards in use within a given location, different REN units are used. When referring to a telephone set, subscriber's equipment or a Ring Generator's REN, the relevant Telecom standard should be identified.

In order to determine the REN for North America, four different calculations are used:

• 25MW divided by the minimum measured on-hook DC resistance for an applied voltage of up to 100 volts.
• 150W divided by the minimum measured on-hook DC resistance for applied voltage of up to 200 volts.
• 0.6mA divided into the maximum DC current drawn during the AC on-hook impedance test.
• 8KW divided by the minimum AC impedance measured while performing the AC on-hook impedance test (for "B" type ringer).

The largest of these four numbers is listed on the label as the REN of the device. If the AC impedance yields the highest REN (as it usually does), it is followed by a letter corresponding to the type of ring signal applied during testing. For example, if the highest REN calculated was 0.8, and the device was tested as a B type ringer, the REN would be 0.8B.

How to determine the required Ringing Frequency?

Ringing signals transmitted over public telephone networks are generally governed by the local authorities and are specified in the telecom standards. Before designing a system, one should consult the telecom standards that apply at the system's destination in order to determine which ringing frequency is required. Note that PowerDsine Ring Generators support all popular international ringing frequencies. Most models are equipped with a digitally selectable output frequency option. This feature is especially valuable for systems that are aimed at a variety of destinations.

Which safety standards do PowerDsine components meet?

The highest standards of quality ensure proven PowerDsine reliability. PowerDsine is ISO9001 certified, and its subcontractors carry ISO9002 certification. All products meet UL1950, CSA22.2.950, and EN60950 Telecom and safety requirements as well as Bellcore 63 and Bellcore 78 Standards.

How to calculate the required ringing signal amplitude for my design?

Most modern telephone sets, modems and facsimile machines will recognize the Ringing Signal at amplitude of 35Vrms and above. A few facsimile models, and some older telephone sets will require minimum amplitude of 40Vrms or even 45Vrms to ring. When calculating the required output amplitude of a Ring Generator, the objective should be to deliver more than the minimum ringing amplitude to the loop's end. The voltage drop on the loop can be calculated according to the typical line resistance, the loop length, connection resistance and the sum of the line's serial protection resistors. Higher ring generator output amplitude can support longer loops. However, since ring generators are limited for specified output wattage and since telephone devices are current driven, lower output amplitude will allow for higher output current that translates to a higher REN.

How to calculate the Power Factor of a telephone set, and how does it effect the Ring Generator?

Telephone ringing elements include resistance, capacitance and in some cases inductance elements. A ringing element's Power Factor (PF) expresses the amount of phase shift between the AC voltage and the AC current caused by the device. The PF is a function of the ratio between the real and imaginary elements of the ringing element's impedance. Higher capacitance or inductance components in comparison to the resistance component will cause a larger phase shift and be expressed as lower PF. A PF of 1 will cause no phase shift, and indicate that the device has no capacitance and inductance elements, or that both exist and exactly cancel each other's effects. The PF of a ringing element, which includes resistance in series to capacitance, can be obtained by using the following equation:

Higher phase shift between the Ring Generator's output voltage and current will cause its output stage to absorb more energy and to generate more heat. PowerDsine Ring Generators are specified for PF=0.5 and are tested for nondestructive continuous operation at a PF=0.3.