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Cisco Inline Power
Cisco Inline Power is often called Cisco prestandard PoE. The major difference between the PoE methods lies primarily in the device detection process. Cisco prestandard PoE uses the following method:
1. The Cisco prestandard PoE device physically connects to the switch.
2. The switch sends an Fast Link Pulse (FLP) tone signal to the device. Only an unpowered. Cisco prestandard PoE device will loop this tone back.
3. When the switch receives the tone back, it realizes the device is an unpowered Cisco prestandard PoE device and applies a minimal amount of power (6.3W) to the line.
4. The unpowered device boots and communicates its actual power requirements to the switch using the Cisco Discovery Protocol (CDP).
If CDP is disabled on the switch (or the connecting device does not support CDP), the switch automatically allocates the maximum amount of power (15.4W) to each port. The device will use only the power it needs; the test of the power is wasted. If all the ports attempt to use the full 15.4W of power, the switch will run out of power before all ports can receive it. In this case, the upper port numbers will remain unpowered.
802.3af Power over Ethernet
Rather than using a FLP tone to detect an unpowered PoE device, 802.3af uses a small DC current that is constantly applied to the line. Non-PoE devices are not harmed by this DC current. An 802.3af-capablc device will be equipped with a resistor that returns a specific level of resistance to the line. When the switch defects this resistance level, it will know how much power to send to the attached device. This power can be sent at four different levels.
802.3af PoE is able to send power over all four pairs of wire in an Ethernet cable, thus sharing the same wires as the data. This allows 802.3af to function even over Gigabit Ethernet (1000BASE-T).
Cisco Inline Power is often called Cisco prestandard PoE. The major difference between the PoE methods lies primarily in the device detection process. Cisco prestandard PoE uses the following method:
1. The Cisco prestandard PoE device physically connects to the switch.
2. The switch sends an Fast Link Pulse (FLP) tone signal to the device. Only an unpowered. Cisco prestandard PoE device will loop this tone back.
3. When the switch receives the tone back, it realizes the device is an unpowered Cisco prestandard PoE device and applies a minimal amount of power (6.3W) to the line.
4. The unpowered device boots and communicates its actual power requirements to the switch using the Cisco Discovery Protocol (CDP).
If CDP is disabled on the switch (or the connecting device does not support CDP), the switch automatically allocates the maximum amount of power (15.4W) to each port. The device will use only the power it needs; the test of the power is wasted. If all the ports attempt to use the full 15.4W of power, the switch will run out of power before all ports can receive it. In this case, the upper port numbers will remain unpowered.
802.3af Power over Ethernet
Rather than using a FLP tone to detect an unpowered PoE device, 802.3af uses a small DC current that is constantly applied to the line. Non-PoE devices are not harmed by this DC current. An 802.3af-capablc device will be equipped with a resistor that returns a specific level of resistance to the line. When the switch defects this resistance level, it will know how much power to send to the attached device. This power can be sent at four different levels.
802.3af PoE is able to send power over all four pairs of wire in an Ethernet cable, thus sharing the same wires as the data. This allows 802.3af to function even over Gigabit Ethernet (1000BASE-T).
| Cisco IP Phone Model | PoE Type |
| 7906G | Cisco prestandard or 802.3af |
| 7911G | Cisco prestandard or 802.3af |
| 7914/7915/7916 Expansion Modules | Local power only |
| 7931G | 802.3af only |
| 7937G Conference Station | 802.3af only |
| 7940G | Cisco prestandard only |
| 7941G | Cisco pre standard or 802.3af |
| 7941G-GE | 802.3af only |
| 7942G | Cisco prestandard or 802.3af |
| 7945G | 802.3af only |
| 7960G | Cisco prestandard only |
| 7961G | Cisco pre standard or 802.3af |
| 7961G-GE | 802.3af only |
| 7962G | Cisco prestandard or 802.3af |
| 7965G | 802.3af only |
| 7970G | Cisco prestandard or 802.3af |
| 7971G-GE | 802.3af only |
| 7975G | 802.3af only |
| 7985G | 802.3af only |
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