Cisco Catalyst 3750 Hardware Installation Manual page 29

Chapter 1 Product Overview
10/100 and 10/100/1000 Ports
Voltages that present a shock hazard may exist on Power over Ethernet (PoE) circuits if
Warning
interconnections are made using uninsulated exposed metal contacts, conductors, or terminals.
Avoid using such interconnection methods, unless the exposed metal parts are located within a
restricted access location and users and service people who are authorized within the restricted
access location are made aware of the hazard. A restricted access area can be accessed only through
the use of a special tool, lock and key or other means of security. Statement 1072
The 10/100 ports on the Catalyst 3750-24PS and 3750-48PS switches and the 10/100/1000 ports on the
Catalyst 3750G-24PS, 3750G-48PS, 3750G-24WS-S25, and 3750G-24WS-S50 switches provide PoE
support for devices compliant with IEEE 802.3af and also provide Cisco pre-standard PoE support for
Cisco IP Phones and Cisco Aironet Access Points.
Each of the Catalyst 3750-24PS switch 10/100 ports or the Catalyst 3750G-24PS switch 10/100/1000
ports can deliver up to 15.4 W of PoE. On the Catalyst 3750-48PS or 3750G-48PS switches, any 24 of
the 48 10/100 or 10/100/1000 ports can deliver 15.4 W of PoE, or any combination of the ports can
deliver an average of 7.7 W of PoE at the same time, up to a maximum switch power output of 370 W.
Each of the Catalyst 3750G-24WS-S25 and 3750G-24WS-S50 switch 10/100/1000 ports can deliver up
to 15.4 W of PoE.
On a per-port basis, you can control whether or not a Catalyst 3750 PoE port automatically provides
power when an IP phone or an access point is connected. The device manager and the CLI provide two
PoE settings for each 10/100 or 10/100/1000 PoE port: Auto and Never.
When you select the Auto setting, the port provides power only if a valid powered device, such as an
IEEE 802.3af-compliant powered device, a Cisco pre-standard IP phone, or a Cisco pre-standard Cisco
access point, is connected to it. The Auto setting is the default. However, when you select the Never
setting, the port does not provide power even if a Cisco IP phone or an access point is connected to it.
For information about configuring and monitoring PoE ports, see the device manager online help and the
switch software configuration guide.
Cisco enhanced power negotiation allows some powered devices, such as the Cisco 7970G IP Phone, to
operate in high-power mode on Catalyst 3750 PoE switches. The powered device and the switch
negotiate through power-negotiation Cisco Discovery Protocol (CDP) messages for an agreed-upon
power-consumption level. The negotiation allows a high-power Cisco powered device that consumes
more than 7 W to operate at its highest power mode. The powered device first boots up in low-power
mode, consumes less than 7 W, and negotiates to obtain enough power to operate in high-power mode.
The device changes to high-power mode only when it receives confirmation from the switch. High-power
devices can operate in low-power mode on switches that do not support power-negotiation CDP.
For information about configuring and monitoring PoE ports, see the device manager online help and the
switch software configuration guide.
You also can connect a Cisco IP Phone or Cisco Aironet Access Point to a Catalyst 3750 PoE switch
Note
10/100 or 10/100/1000 port and to an AC power source for redundant power. The powered device might
change to the AC power source as its primary power source when connected to it. In that case, the PoE
port becomes the backup power source for the powered device.
If the primary source fails, the second power source becomes the primary power source to the powered
device. During the power transfer, an IP Phone might reboot or reestablish link with the switch.
For information about Cisco IP Phones and Cisco Aironet Access Points, see the documentation that
came with your IP phone or access point.
Catalyst 3750 Switch Hardware Installation Guide
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