Dell PowerConnect 55xx Systems User Guide 491Voice VLANThe Voice VLAN feature enables you to enhance VoIP service by configuringports to carry IP-voice traffic from IP phones on a specific VLAN. This VLANis configured with a QoS profile that ensures high voice quality.Equipment, such as VOIP phones, transmits IP traffic with a pre-configuredOrganizational Unique Identifier (OUI) prefix in the source MAC address.This enables the switch to dynamically identify ports connected to the VoIPequipment and automatically add these ports to the Voice VLAN.IP phones use one of the following modes, both of which are supported by thedevice:• Use only tagged packets for all communications.• Initially use untagged packets while retrieving the initial IP addressthrough DHCP. Then the phone uses the Voice VLAN and starts sendingtagged VoIP packets.Non-VoIP traffic is dropped from the Voice VLAN when the device is in AutoVoice VLAN secured mode.The Voice VLAN feature also provides QoS actions to VoIP, ensuring that thequality of voice does not deteriorate if the IP traffic is received unevenly.To summarize, when Voice VLAN is enabled and configured, and VoIPequipment is connected to one of the switch ports, the VoIP traffic triggersthe switch’s Voice VLAN feature to add this port to the Voice VLAN (a VLANthat usually carries only voice traffic), and to assign traffic from this port aspecific QoS profile, ensuring high voice quality.The device supports a single voice VLAN.
