Allied Telesis AT-GS950/8POE - Manual (Page 23)

AT-GS950/8POE Gigabit Ethernet WebSmart Switch Installation Guide
23
Power Budgeting The AT-GS950/8POE switch provides a maximum of 15.4 W of power per
port on four of the eight ports for a total power consumption of 62 W, while
at the same time furnishing standard 10/100 Mbps Ethernet functionality.
The AT-GS950/8POE switch power management functionality supports
any combination of Ethernet ports (1-4) that supply power for IEEE 802.3af
Class 0, 1, 2, or 3 powered devices up to a maximum of 62 watts, as
described in Table 2.
Note
Power is supplied to the powered devices in the order that the ports
are connected or on a first-come-first-served basis until the 62 watt
limit is reached. If the switch is power cycled after the PoE devices
are connected to the switch ports, the power is supplied to ports 1
through 4 in ascending order.
Implementation
A standard Ethernet twisted pair cable contains four pairs of strands for a
total of eight strands. 10/100 Mbps network traffic requires only four
strands (1, 2, 3, and 6), leaving four strands in the cable unused (4, 5, 7,
and 8).
The PoE standard, IEEE 802.3af, describes two alternative ways for
delivering power to a powered device (PD) over twisted pair cabling.
Alternative A uses the same strands that carry the network traffic.
Alternative B uses the spare strands. The PoE implementation on the
AT-GS950/8POE switch is Alternative B, where power is transmitted over
strands 4, 5, 7, and 8.
PDs that comply with the IEEE 802.3af standard typically support both
power delivery methods. When a PD is compliant with the standard, it
receives its power from the switch using either a straight or cross-over
cable. The PoE feature on the AT-GS950/8POE switch works with most
legacy PD’s as long as the device can be powered on pins 4, 5, 7, and 8.
Table 2. IEEE 802.3af Class vs. Power Levels
Class Usage
Minimum Power
Levels Output at
the PSE
Maximum Power
Levels Output at
the PD
0 Default 15.4W 0.44W to 12.95W
1 Optional 4.0W 0.44W to 3.84W
2 Optional 7.0W 3.84W to 6.49W
3 Optional 15.4W 6.49W to 12.95W