UPOE Architecture
As defined in IEEE 802.3af and IEEE 802.3at, PoE delivers electrical power over two pairs out of the four twisted pairs of cable in Class D (also known as Cat5e) or better, cabling as specified in ISO/IEC 11801:1995. A PSE uses only signal pairs, the pairs 1, 2 and 3, 6, to transport power from the PSE to the PD and leaves the spare pairs, the pairs 4, 5 and 7, 8, idle. This architecture can deliver up to 30W per port. (Refer to Figure 5.)
Figure 5. PoE and PoE+ Architecture
UPOE uses the same cabling standard as PoE. Instead of delivering power over two twisted pairs, it provides the capability to source up to 60W of power by using all the four pairs of standard Ethernet cabling (Cat5e or better).
The architecture for a 4-pair system is pretty straightforward; it is an extension of the 2-pair design. The 2-pair system uses one PSE controller to power the PD through the signal pairs of the cable. In the new 4-pair system two PSE controllers will be used to power both the signal pairs and the spare pairs. Figure 6 shows the UPOE architecture.
Figure 6. UPoE Architecture
Table 1 summarizes the primary comparison between PoE, PoE Plus, and UPOE.
Table 1. PoE/PoE Plus/UPOE comparison
PoE
|
PoE Plus
|
UPOE
| |
Minimum cable type
|
Cat5e
|
Cat5e
|
Cat5e
|
IEEE standard definition
|
802.3af
|
802.3at
|
Cisco proprietary
|
Maximum power per PSE port
|
15.4W
|
30W
|
60W
|
Maximum power to PD
|
12.95W
|
25.5W
|
51W
|
Twisted pair used
|
2-pair
|
2-pair
|
4-pair
|
UPOE Operation
This section describes the UPOE operation steps to detect, classify, and negotiate power and subsequently power up the PD.
PD Detection, Classification
The hardware detection and classification mechanism for UPOE follows the IEEE 802.3 standard. The PSE and the PD use a set of physical layer mechanisms to detect the connection of the endpoint and subsequently classify the endpoints into different categories that map to different levels of power requirements. Table 3 lists the PoE classes.
Table 3. PoE Classes
Class
|
Usage of class
|
Minimum Power Levels Output at the PSE
|
Maximum Power Levels at the Powered Device
|
Class description
|
0
|
Default
|
15.4W
|
0.44 to 12.95W
|
Classification unimplemented
|
1
|
Optional
|
4.0W
|
0.44 to 3.84W
|
Very Low Power
|
2
|
Optional
|
7.0W
|
3.84 to 6.49W
|
Low Power
|
3
|
Optional
|
15.4W
|
6.49 to 12.95W
|
Mid Power
|
4
4
|
Reserved in 802.3af
802.3at
|
Treat as Class 0
30W
|
12.95W to 25.5W
|
High Power
|
At power-on, a UPOE device is treated as a PoE device and allocated 15.4W as the default power. After power-on the PSE and PD go through a power negotiation phase to determine exactly how much power will be provisioned from the PSE to the PD.
