Specifying PoE switches for Biamp Tesira devices

Initial considerations

In addition to ensuring network switches can handle the traffic that is intended to be transmitted through them, it is important to make sure the switches can power all the connected PoE devices.

PoE (Power Over Ethernet) is a set of standards developed by the IEEE under the 802.3 publication that describes power provision over Ethernet.

PoE Budget is a specification of network switches and multi-port PoE injectors. This power budget is a shared resource available as needed to all ports. Each PoE device negotiates power needs with the switch or PoE injector based on the class of the device. The device is then provided with power from the PoE budget accordingly.

PoE budget may be exceeded during system operation if a network switch is not properly specified. This will cause the switch to turn off PoE on one and possibly all the ports. The communication with endpoint devices will be interrupted and Tesira performance could be temporarily or even permanently compromised.

The terms PoE and PoE+ have some overlap in meaning. For this reason, PoE and PoE+ equipment will be generically referred to as “PoE equipment” throughout this article.

Calculating PoE device counts

Calculating how many devices a single network switch can power will help identify how many switches are required to power all the PoE devices in the system.

Please follow these steps:

1. Check the total PoE budget of the switch in the manufacturer's specification.

2. Check the Biamp endpoint device's PoE class using the provided technical documentation (Datasheet/Manual), this Tesira PoE devices reference chart or the online PoE budget calculator.

3. Make note of the "Max Power From Switch" value for the PoE class of your selected endpoint devices. *

4. Divide the total PoE budget by "Max Power From Switch" figure. The result will show how many PoE devices the switch can power.

5. Make sure the PoE class is supported on the needed number of ports. **

* When planning the PoE budget of switches, it is important to distinguish between the “Max Consumption” and “Max Power From Switch” values. "Max Power From Switch" shows the actual power that the switch port may have to deliver so the endpoint PoE device still receives sufficient power after line-loss in the 100m cable.

The Tesira TCM-1A and AMP-450P are 802.3at Class 4 devices with built-in amplifiers and will draw the maximum power available from the switch port during heavy workloads or while recharging the power reserve. Budget the full 30W per port even though they may only draw 7W in an idle state if the device will be operated under heavy load.

Note that some manufacturers provide a maximum power value for devices which is lower than the maximum as defined by the PoE class. For example, a device may be classified as 802.3at Class 4, but has a maximum draw of 16W as opposed to 30W. Adjust the maximum power figure of 16W by adding 16% to account for possible line loss. This is the “Max Power From Switch” for this device.

** Even if it’s calculated that 380W of PoE budget on the selected 24-port switch is sufficient to power 12 x Class 4 endpoint devices, the switch specifications may have a maximum of 4 ports that support 802.3at Class 4. Therefore, only 4 x Class 4 devices may be connected to the switch as per the manufacturer’s specification.

Tesira PoE devices

Use the chart below for reference information on PoE classes and the maximum power draw of Biamp Tesira devices (listed in alphabetical order):

PoE injectors

If planning to include just a few PoE devices in a system, consider using a non-PoE network switch with PoE injectors instead of a switch with full PoE support on all ports. This may help to reduce the overall cost of the system.

The algorithm for determining the correct PoE injectors is similar to selecting PoE network switches:

• If using single-port PoE injectors, check that each injector supports the PoE class of the selected device and thereby provides the "Max Power From Switch" for the device.
• Multi-port PoE injectors (sometimes referred to as PoE Injector Hubs) usually have a total PoE budget specification just like PoE network switches. This budget specification may be used in the same manner as described above.

Important! Note that there are passive PoE injectors that do not negotiate the PoE class with the connected PoE device and just provide continuous power right after the connection.

Passive PoE injectors can permanently damage connected devices in some cases and should generally be avoided or at least be used with caution.

These injectors do not comply with any particular PoE standard, so you must check the documentation for the exact power they provide and compare it to the power that your device requires before connecting it to a passive injector.

Daisy-chained Parlé microphones

TCM-1 and TCM-1A head models have the ability to connect up to three microphones on one switch port in a daisy-chain. However, the PoE class of the device remains the same, regardless of the number of daisy-chained microphones.

• TCM-1 head microphone is considered as a single 802.3at Class 3 device, regardless of the number of connected TCM-1EX microphones:

• TCM-1A microphone is considered as a single 802.3at Type 2 - Class 4 device, regardless of the number of connected TCM-1EX microphones:

TCM-X and TCM-XA network boxes have the ability to connect up to two microphones on one switch port. However, the PoE class of the device remains the same, regardless of the number of connected microphones.

• TCM-X network box is considered as a single IEEE 802.3af Class 3 device regardless of the number of connected TCM-XEX microphones.

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• TCM-XA network box is considered as a single IEEE 802.3at Type 2 - Class 4 device regardless of the number of connected TCM-XEX microphones.

TTM-X network boxes have the ability to connect up to two microphones on one switch port. However, the PoE class of the device remains the same, regardless of the number of connected microphones.

• TTM-X network box is considered as a single IEEE 802.3af Class 3 device regardless of the number of connected TTM-XEX microphones.

Troubleshooting

The PoE network switch or injector automatically negotiates and provides power to the endpoint device. If the PoE device does not power on, reboots repeatedly, or is not responding as expected, there may be a PoE negotiation problem. Consider the following when troubleshooting:

Further reading

• Power over Ethernet (PoE)
• Parlé-series Beamtracking Microphones
• Tesira PoE Power Budget Calculator