Chapter 1: Overview
Power Budgeting The power for PoE on the ports on the AT-SBx81GP24 Line Card is provided by the AT-SBxPWRPOE1 Power Supply. It can provide up to 1200 watts of power for powered devices. You may install up to two power supplies in the chassis for a total of 2400 watts for the powered devices.
The number of powered devices the chassis can support at one time depends on the number of AT-SBxPWRPOE1 Power Supplies in the chassis and the power requirements of the powered devices in your network. Table 4 lists the maximum number of powered devices by class, for one or two power supplies. The numbers assume that the powered devices require the maximum amount of power for their classes.
Note
The maximum number of PoE ports in the SwitchBlade x8112
Switch is 240 ports.
Table 4. Maximum Number of Powered Devices
| | Maximum Number of | Maximum Number of |
| Class | Ports with | Ports with |
| One PoE PSU | Two PoE PSU’s |
| |
| | (1200 W) | (2400 W) |
| | | |
| | | |
| 0 | 77 | 155 |
| | | |
| 1 | 240 | 240 |
| | | |
| 2 | 171 | 240 |
| | | |
| 3 | 77 | 155 |
| | | |
| 4 | 40 | 80 |
| | | |
PoE Wiring The IEEE 802.3af and 802.3at standards define two methods for delivering power to powered devices over the four pairs of strands that comprise a standard Ethernet twisted-pair cable. The methods are called Alternatives A and B. In Alternative A, power is supplied to powered devices on strands 1, 2, 3, and 6, which are the same strands that carry the 10/100Base-TX network traffic. In Alternative B, power is delivered on strands 4, 5, 7, and 8. These are the unused strands.
Note
1000BASE-T cables carry the network traffic on all eight strands of the Ethernet cable.
The PoE implementation on the AT-SBx81GP24 Line Card is Alternative
A. Power is transmitted on strands 1, 2, 3, and 6.
