DELL PC7024 User Manual

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 LLDP-

MED 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.

2CSPC4.XCT-SWUM2XX1.book  Page 809  Monday, October 3, 2011  11:05 AM