Dell PowerConnect 5548 User Guide - Page 491

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