Cisco 3750G-12S Hardware Installation Guide - Page 21

Chapter 1 Product Overview 10/100 and 10/100/1000 Ports On 24-port switches, the ports can deliver up to 15.4 W of PoE. On the 48-port switches, any 24 of the 48 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 PoE ports can deliver up to 15.4 W of PoE. On a per-port basis, you can control whether 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 (the default) and Never. • When you select Auto, the port only provides power 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. • When you select Never, 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. Note You also can connect a Cisco IP Phone or Cisco Aironet Access Point to a Catalyst 3750 PoE switch 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. Note 100BASE-TX and 1000BASE-T traffic requires a Category 5 or later cable. 10BASE-T traffic can use Category 3 or Category 4 cables. When you connect the switch to workstations, servers, routers, and Cisco IP Phones, be sure that the cable is a straight-through cable. When you connect the switch to switches or hubs, use a crossover cable. When using a straight-through or crossover cable for 1000BASE-T connections, be sure to use a twisted four-pair, Category 5 or later cable for proper operation. Pinouts for the cables are described in Appendix A, "Technical Specifications." OL-6336-10 Catalyst 3750 Switch Hardware Installation Guide 1-11