Power Over Ethernet (Poe) Overview; Poe Terms And Standards; Poe Sensing; Power Management - Symbol ES3000 Manual

4-2 ES3000 Advanced Concept Guide

4.1 Power over Ethernet (PoE) Overview

4.1.1 PoE Terms and Standards

Power over Ethernet (PoE) supplies power to Ethernet devices directly through the Ethernet data
cable. PoE distinguishes between two types of equipment: power-supply equipment (PSE), such as
the ES3000 switch, and a powered device (PD), such as an access point. If the powered device
requires power, the PSE injects the current into the cable, and the powered device can operate solely
through the power it receives from the data cable.
The standard for PoE is IEEE 802.3af. The ES3000 switch is compliant with this standard.

4.1.2 PoE Sensing

ES3000 switch can sense whether a powered device is attached to a port. The switch supplies power
only to devices that need it. The switch initially uses resistance detection (802.3af) to determine
whether a port requires power. If that fails, and if capacitance detection is enabled, the switch then
uses capacitance detection to determine whether the port needs power. This allows the switch to
detect the presence of legacy powered devices, which might not be 802.3af compliant.

4.2 Power Management

4.2.1 Power Management Overview

The ES3000 switch has a maximum PoE power budget of 170 watts. This is enough to supply 7 watts
to all 24 PoE ports on the switch. The switch supplies a maximum of 16.5 watts per port.
When a new powered device is connected to a port, the ES3000 switch checks whether enough
power remains in the power budget to support the device. This decision is based on the actual power
drawn by the powered devices at the time of connection, rather than their maximum power
consumption. Each powered device will usually draw less power than it maximum limit.
If there is insufficient power to supply all PoE-enabled ports, the switch does not power all ports. The
administrator can select the method the ES3000 switch uses to decide which ports receive power;
see "Configuring the Switch Policy" on page 4.
The web interface has two configuration pages. The PoE Port Configuration page allows the
administrator to manage and monitor power restrictions for individual ports. The PoE Global
Configuration page allows the administrator to set PoE management policies that affect the entire
switch.