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Biamp Systems

Power over Ethernet (PoE)

Power over Ethernet (PoE) was originally developed to provide power along with data to locations where AC power would be inconvenient, expensive, or infeasible to install. However, even in situations where AC power is feasible, PoE offers some extra advantages.

PoE is simple to set up and does not require a qualified electrician to install because it operates at a low voltage. Another benefit is that the data and power are confined to a single cable, which means cabling requirements are reduced, and as an extra benefit, existing network infrastructure can be used in most cases.

The flexibility that PoE offers by combining network signal and power into a single Ethernet cable shows there are many great incentives to using this technology and make it a highly desirable attribute in today’s market.

PoE provides a minimum of 12.95 Watts at 44V DC to each device. PoE+ provides a minimum of 25.5 Watts at 50V DC to each device. PoE+ devices will not function properly on PoE power.

Biamp uses the IEEE 802.3af Type 1 standard for PoE devices across the Audia, Nexia, Vocia product range.

For Tesira, the EX-Logic and TEC-1 devices also use the IEEE 802.3af Type 1 standard, while all other Tesira Expanders require the IEEE 802.3at Type 2 Class 4 (also known as PoE+).

PoE sources

There are three main types of PoE sources in use today, all are compatible with CAT5, CAT5e and CAT6 cable. Each solution has its own benefits and the solution you choose depends on the existing infrastructure and the number of PoE devices that will eventually be connected.

PoE Switch (PoE Endspan)

The most preferable option, especially if new networking hardware is required. A PoE switch looks like your average Ethernet switch, however it provides an all-in-one source for data and power. Typically this is the most economical option when powering multiple PoE devices.

Standard connection of a PoE Switch to a PoE device.

Single-Port Midspan (PoE Injector)

A Single-Port Midspan is designed to be used in-line with the Ethernet cable to provide power to a single device and suits applications where there aren't enough PoE devices to warrant the cost of a PoE Switch, or, if the data needs to first be transmitted a long distance (e.g. via fiber), before being converted back to Ethernet, and then PoE applied.

The downside to using a Single-Port Midspan is the requirement for a mains outlet to operate, and the tendency to become costly when more than a few devices require power.

Standard connection of a Single-Port PoE Midspan to a PoE device.

Multi-Port Midspan (PoE Injector)

The Multi-Port Midspan was developed to “inject” power into an existing Ethernet network where the existing Ethernet switch does not provide PoE capability. The Midspan box sits between an existing Ethernet switch and the PoE devices.

Standard connection of a Multi-Port PoE Midspan to a PoE device.

PoE and PoE+ IEEE standards

Biamp uses the IEEE 802.3af Type 1 standard for PoE devices across the Audia, Nexia, Vocia product range.

For Tesira, the EX-Logic and TEC-1 devices also use the IEEE 802.3af Type 1 standard, while all other Tesira Expanders require the IEEE 802.3at Type 2 Class 4 (also known as PoE+).

The standard used can be determined by the Class identified in the product manual or on the product data sheet. The vast majority of manufacturers offering PoE solutions conform to the standard and you can be assured if the switch or midspan injector you’re purchasing lists this operating standard, your Biamp device should perform correctly. Due to power dissipation the maximum distance any single Ethernet cable run can be is 328 ft (100m) from the PoE source. Also, if this distance is exceeded, data communications could be negatively affected as well.

The PoE IEEE 802.3af Type 1 standard provides a minimum of 12.95 Watts at 44V DC to each device. 12.95 Watts of a maximum 15.4 Watts is assured to be available at the PoE device, allowing for power dissipation / loss in the cable.

For PoE+ IEEE 802.3at Type 2 Class 4 standard provides a minimum of 25.5 Watts at 50V DC to each device. 25.5 Watts of a maximum 34.2 Watts is assured to be available at the PoE+ device, allowing for power dissipation / loss in the cable.

The PoE discovery process

Non-PoE devices will not be affected if they are connected to a PoE network due to the three operation states of PoE; detection, classification, and operation.

During detection, the PoE source will leave the Ethernet cable unpowered while it periodically looks to see if something has been plugged in. The low level of power used during this detection period is unlikely to damage a device not designed for PoE. In addition, over-current protection, under-current detection and fault protection from shorts, power fluctuation or failure is also monitored. If a valid PoE signature is found present, then the PoE source may inquire how much power is required by the device; this is referred to as classification. The device may return a default full-power signature (Class 0), or one of four other choices before moving on to the operation stage, where the device becomes fully functional.

Available wattage is important

Most PoE sources will deliver the full 15.4 Watts (Type 1) or 34.2 Watts (Type 2) across all ports, however, be aware some PoE sources may list a maximum wattage they are able to provide, and this is when the class of device becomes important. The minimum wattage a PoE source is required to supply can be determined by the total number and class of PoE devices that will eventually be connected to it.

To calculate the minimum wattage your PoE source must be able to deliver, use the following formula and table:

(Total devices in a distinct class) x (power output from PoE source of that distinct class) = total watts required (for that selected class).

Now, repeat this formula for the next class of devices, and the next, etc. Finally, sum the total watts required by each class to find the minimum power rating for the PoE source.

Class

Usage

Min Power Requirement

of Device [Watts]

Power Output from

PoE Source [Watts]

Class description

0

Default

12.95

15.40

-

1

Optional

3.84

4.45

Very Low power

2

Optional

6.49

7.52

Low power

3

Optional

12.95

15.40

Mid power

4

Valid for 802.3at devices
(Type 2 only)

25.50

34.20

High power

Example: if you had three class 0 devices and two class 2 devices;

(3 x 15.40 Watts) + (2 x 7.52 Watts ) = 61.24 Watts

The minimum rating for the PoE source should be 61.24 Watts

The class of any Biamp device can be found on its respective Product Data Sheet or Product Manual.

Power Management (EEE)

Ensure that any PoE switch used with Biamp devices either will allow you to defeat EEE (Energy Efficient Ethernet) functionality or does not have this feature. So-called "green" switches will not provide constant power to the Biamp devices. Devices will become non-functional as a result of the switch putting their PoE port into a low-power "sleep" state.

Data and power pinout

In an Ethernet cable, four twisted pairs are used as the medium for transmission. The actual data transmission only takes up two pairs of wires (pairs 1-2 and 3-6). The PoE source can apply voltage either between the RX and TX pairs (Mode A: pins 1–2 and 3–6), or between the two spare pairs (Mode B: pins 4–5 and 7–8).

Power must only be applied to one set of pairs at a time and this decision is made by the PoE source device. From an end user's point of view, the mode selected is not a concern because it is a requirement of the IEEE standard that all devices must be able to accept power in Mode A or Mode B form, however both modes must not be supplied at the same time.

Pin

Mode A

Mode B

1

Positive

-

2

Positive

-

3

Negative

-

4

-

Positive

5

-

Positive

6

Negative

-

7

-

Negative

8

-

Negative

4 PoE data and power pinout standards.png

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