Dell PowerConnect 7000 Series, Reference Manual

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Voice VLAN Commands
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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