Catalyst Switch Role in IP Telephony

Cisco voice-capable Catalyst switches can provide three primary features to assist you with your IP telephony deployment:

• Inline power Inline power capabilities allow a Cisco Catalyst switch to send power through the Category 3 (or better) copper cabling to a Cisco IP Phone or other inline power-compatible devices (such as wireless access points) without the need for an external power supply. Inline power is also referred to as Power over Ethernet (PoE). Inline power was developed in 2000 by Cisco to support the emerging IP telephony solution and was later standardized by the IEEE as the 802.3af standard.
• Auxiliary VLAN support Auxiliary VLAN support allows a switch to support multiple VLANs on a single access port. You can connect a PC to the back of the Cisco IP Phone because some Cisco IP Phones have built-in switches. Auxiliary VLANs allow you to place the IP Phone, and the devices that are attached through the IP Phone, on separate VLANs.
• Class of service (CoS) marking CoS marking is data link layer (Layer 2) marking that is used to prioritize network traffic. Prioritizing voice traffic is critical in IP telephony networks. If voice traffic is not given priority, poor voice quality may result because voice frames wait in the switch queue behind large data frames. The switch can use existing CoS marking to prioritize network traffic and can also classify and mark traffic that it receives.