Dell PowerConnect 8100 CLI Reference Guide - Page 829

37 Voice VLAN Commands The Voice VLAN feature enables switch ports to carry voice traffic with an administrator-defined priority so as to enable prioritization of voice traffic over data traffic. Using Voice VLAN helps to ensure that the sound quality of an IP phone is protected from deterioration when the data traffic utilization on the port is high. Voice VLAN is the preferred solution for applying QoS to voice traffic in an enterprise environment. Voice VLAN scales with the number of ports and does not make significant demands on the switch CPU for classification of voice traffic. However, Voice VLAN does require the administrator to perform the additional configuration step of defining the QoS policy to be applied to voice traffic. The switch can be configured to support voice VLAN on a port connecting to the VoIP phone. When a VLAN is associated with the voice VLAN port, then the VLAN ID information is passed onto the VoIP phone using the LLDPMED mechanism. The voice data coming from the VoIP phone is tagged with the exchanged VLAN ID; thus, regular data arriving on the switch is given the default PVID of the port, and the voice traffic is received on a predefined VLAN. The two types of traffic are therefore segregated so that better service can be provided to the voice traffic. When a dot1p priority is associated with the voice VLAN port instead of VLAN ID, then the priority information is passed onto the VoIP phone using the LLDP-MED mechanism. Thus, the voice data coming from the VoIP phone is tagged with VLAN 0 and with the exchanged priority. Regular data arriving on the switch is given the default priority of the port (default 0), and the voice traffic is received with higher priority, thus segregating both the traffic to provide better service to the voice traffic. The switch can be configured to override the data traffic CoS. This feature enables overriding the 802.1P priority of the data traffic packets arriving at the port enabled for voice VLAN. Thus, a rogue client that is also connected to the voice VLAN port does not deteriorate the voice traffic. Voice VLAN is recommended for enterprise-wide deployment of voice services on the IP network. Voice VLAN Commands 829