Information Technology Reference
In-Depth Information
Switch/Hub
Powered End Station
1
3
Data Pair
Data Pair
2
6
-
Power
Sourcing
Equipment
(PSE)
Powered
Device
(PD)
+
1
3
Data Pair
Data Pair
6
2
FIGURE 13.10
Power-over-Ethernet phantom connection. (Source: IEEE 802.3af.)
device that PoE is available, and the rest is not rocket science—just good engineer-
ing to make the connection work just as if the power circuitry wasn't there. A sam-
ple configuration of this scheme is shown in Fig. 13.10.
Another alternative uses spare pairs in the cable bundle to supply the power to
the DTE. As you know, many LAN topologies can get by with only two of the four
pairs in the cable. The trick here is to simply use the extra two pairs to supply
power. The pair assignments are shown in Fig. 13.11.
In PoE, one device, such as a “PoE” hub or switch, provides power to each
connection, and the DTEs (such as an IP phone, a web cam, or an access point)
Switch/Hub
Powered End Station
1
3
Data Pair
Data Pair
2
6
+
4
5
4
5
Power
Sourcing
Equipment
(PSE)
Powered
Device
(PD)
-
7
8
7
8
3
1
Data Pair
Data Pair
6
2
FIGURE 13.11
Power-over-Ethernet spare-pair connection. (Source: IEEE 802.3af.)
 
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