Understanding Power over Ethernet

Power over Ethernet (PoE) is the implementation of the IEEE 802.3 AF and IEEE 802.3 AT standards that allow both data and electrical power to pass over a copper Ethernet LAN cable.

The SRX Series devices support PoE on Ethernet ports. PoE ports transfer electrical power and data to remote devices over standard twisted-pair cable in an Ethernet network. PoE ports allow you to plug in devices that require both network connectivity and electrical power, such as VoIP and IP phones and wireless LAN access points.

You can configure the SRX Series device to act as power sourcing equipment (PSE), supplying power to powered devices that are connected on designated ports.

This topic contains the following sections:

• SRX Series Services Gateway PoE Specifications
• PoE Classes and Power Ratings
• PoE Options

SRX Series Services Gateway PoE Specifications

Table 12 lists the PoE specifications for the SRX210, SRX240 and SRX650 devices

PoE Classes and Power Ratings

A powered device is classified based on the maximum power that it draws across all input voltages and operational modes. When class-based power management mode is configured on the SRX Series devices, power is allocated taking into account the maximum power ratings defined for the different classes of devices.

Table 13 lists the classes and their power ratings as specified by the IEEE standards.

PoE Options

When configuring PoE, you must enable the PoE interface in order for the port to provide power to a connected, powered device. In addition, you can configure the following PoE features:

• Port priority—Sets port priority. When it is not possible to maintain power to all connected ports, lower priority ports are powered off before higher priority ports. When a new device is connected on a higher-priority port, a lower priority port will be powered off automatically if available power is insufficient to power on the higher priority port. (For the ports with the same priority configuration, ports on the left are given higher priority than the ports on the right.)
• Maximum available wattage power available to a port—Sets the maximum amount of power that can be supplied to the port. The default wattage per port is 15.4 watts.
• PoE power consumption logging—Allows logging of per-port PoE power consumption. The telemetries section must be explicitly specified to enable logging. If left unspecified, telemetries is disabled by default. The default telemetry duration is 1 hour. The default telemetry interval is 5 minutes.

• PoE power management mode—Has two modes:

  • Class—When a powered device is connected to a PoE port, the power allocated to it is equal to the maximum power for the class as defined by the IEEE standards.
  • Static—When a powered device is connected to a PoE port, the power allocated to it is equal to the maximum power configured for the port.
• Reserve power—Reserves the specified amount of power for the gateway in case of a spike in PoE consumption. The default is 0.

Related Topics

• Junos OS Feature Support Reference for SRX Series and J Series Devices
• Understanding Ethernet Interfaces
• Example: Configuring PoE on All Interfaces
• Example: Configuring PoE on an Individual Interface
• Example: Deleting a PoE Interface