Alcatel OS6850-P48 User Guide - Page 159

Managing Power over Ethernet (PoE) Understanding Priority Disconnect Understanding Priority Disconnect The priority disconnect function differs from the port priority function described on page 5-7 in that it applies only to the addition of powered devices (PDs) in tight power budget conditions. Priority disconnect is used by the system software in determining whether an incoming PD will be granted or denied power when there are too few watts remaining in the PoE power budget for an additional device. For example, if there are only 2 watts available in the current PoE power budget and a user plugs a 3.5W powered device into a PoE port, the system software must determine whether the device will be powered on. Based on priority disconnect rules, in some cases one or more existing devices may be powered down in order to accommodate the incoming device. In other cases, the incoming device will be denied power. Priority disconnect rules involve the port priority status of an incoming device (i.e., low, high, and critical), as well as the port's physical port number (i.e., 1-24). Understanding priority disconnect rules is especially helpful in avoiding power budget deficits and the unintentional shutdown of mission-critical devices when PDs are being added in tight power budget conditions. For detailed information on how priority disconnect uses port priority and port number criteria for determining the power status of incoming PDs, refer to the illustrated examples on pages 5-10 through 5-11. Reminder. Priority disconnect applies only when there is inadequate power remaining in the power budget for an incoming device. For information on setting the priority disconnect status, refer to the section below. For information on setting the port priority status (a separate function from priority disconnect), refer to "Setting Port Priority Levels" on page 5-7. Setting Priority Disconnect Status By default, priority disconnect is enabled in the switch's system software. For information on changing the priority disconnect status, refer to the information below. Disabling Priority Disconnect When priority disconnect is disabled and there is inadequate power in the budget for an additional device, power will be denied to any incoming PD, regardless of its port priority status (i.e., low, high, and critical) or physical port number (i.e., 1-24). To disable priority disconnect, use the lanpower priority-disconnect command. Since the switch allows you to set priority disconnect status on a slot-by-slot basis, be sure to specify the slot number in the command line. For example, the syntax -> lanpower 2 priority-disconnect disable disables the priority disconnect function on slot 2. Enabling Priority Disconnect To enable priority disconnect, use the lanpower priority-disconnect command. Be sure to specify the slot number in the command line. For example, the syntax -> lanpower 8 priority-disconnect enable enables priority disconnect on slot 8. OmniSwitch 6850/6850E Series Hardware Users Guide June 2011 page 5-9