Cisco WS-SUP32-GE-3B Software Configuration Guide - Page 207

Chapter 14 Configuring Cisco IP Phone Support Default Cisco IP Phone Support Configuration Example: Cisco Prestandard IP Phone When a switching module port detects an unpowered Cisco prestandard IP phone, the switching module reports to the supervisor engine that an unpowered Cisco IP phone is present and indicates which module and port the phone is on. If the port is configured in auto mode, the supervisor engine determines whether there is enough system power available to power up the Cisco IP phone. The power allocation will be the lower value of the default power or the configured port maximum power if a maximum has been specified. If there is sufficient power available, the supervisor engine removes the allocated power from the total available system power and sends a message to the switching module instructing it to provide power to the port. If there is not enough available power for the Cisco IP phone, the supervisor engine sends a message to the switching module indicating that power is denied to the port. Cisco IP phones may have different power requirements. Unless a lower maximum power level has been configured for the port, the supervisor engine initially allocates the configured default of 7 W (167 mA at 42 V) to the Cisco IP phone. When the correct amount of power is determined from the CDP messaging with the Cisco IP phone, the supervisor engine reduces or increases the allocated power. For example, the default allocated power is 7 W. A Cisco IP phone requiring 6.3 W is plugged into a port. The supervisor engine allocates 7 W for the Cisco IP phone and powers it up. Once the Cisco IP phone is operational, it sends a CDP message with the actual power requirement to the supervisor engine. The supervisor engine then decreases the allocated power to the required amount. When you power off the Cisco IP phone through the CLI or SNMP or remove it, the supervisor engine sends a message to the switching module to turn off the power on the port. That power is then returned to the available system power. Example: IEEE 802.3af IP Phone When a switching module port detects an unpowered IEEE 802.3af-compliant IP phone, the module detects the phone's IEEE 802.3af power classification and notifies the supervisor engine of the phone's location and power requirement. If there is sufficient system power available, the supervisor engine allocates the power level indicated by the IEEE class and sends a message to the switching module approving power to the port. If there is not enough available power for the IP phone, the supervisor engine sends a message to the switching module indicating that power is denied to the port. For example, an IEEE 802.3af-compliant IP phone consuming 7.1 W is plugged into a port. The switching module detects the phone and determines that its IEEE power classification is Class 3, which requires between 7.0 W and 15.4 W. The switching module notifies the supervisor engine of the port location and the IEEE classification of the phone. If there is sufficient power available, the supervisor engine removes 15.4 W from the system power and approves power to the port. For this phone, the system is required to reserve an unnecessary 8.3 W due to the broad ranges of the IEEE classification system. If the auto mode is selected for this port with a maximum power level lower than 15.4 W, the Class 3 phone will be denied power. Cisco inline-powered devices that support IEEE 802.3af and CDP can use CDP to override the IEEE 802.3af power classification. In this case, the actual power requirement will be negotiated through CDP to a lower value. Default Cisco IP Phone Support Configuration Cisco IP phone support is disabled by default. When the voice VLAN feature is enabled, all untagged traffic is sent with the default CoS priority of the port. The CoS is not trusted for 802.1P or 802.1Q tagged traffic. OL-11439-03 Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY 14-5