Telephony: Configuring Articulation VLANs
The articulation VLAN affection enables admission ports to backpack IP articulation cartage from an IP phone. When
a about-face is affiliated to a Cisco IP Phone, the buzz sends articulation cartage with layer-3 IP precedence
and layer-2 chic of account (CoS) values, which are both set to 5 for articulation traffic; all
other cartage defaults to 0. Because the complete affection of an IP buzz alarm can adulterate if the
data is anyhow sent, the about-face supports affection of account (QoS) based on IEEE 802.1p CoS
(802.1p provides a apparatus for implementing QoS at the MAC level). The 802.1p acreage is
carried in the 802.1q block header. If you attending at the fields in an 802.1q tag, you will see a field
called the antecedence field, which is area the 802.1p advice goes. QoS uses classification
and scheduling to accelerate arrangement cartage from the about-face in an organized, anticipated manner.
The Cisco IP Buzz is a configurable device, and you can configure it to advanced cartage with
an IEEE 802.1p priority. You can additionally configure the about-face to either assurance or override the
traffic antecedence assigned by a Cisco IP Phone—which is absolutely what I’ll appearance how to do here.
The Cisco buzz basically has a three-port switch: one to affix to the Cisco switch, one to
a PC device, and one to the absolute phone, which is internal.
You can additionally configure an admission anchorage with an absorbed Cisco IP Buzz to use one VLAN
for articulation cartage and addition VLAN for abstracts cartage from a accessory absorbed to the phone—like
a PC. You can configure admission ports on the about-face to accelerate Cisco Discovery Protocol (CDP)
packets that acquaint an absorbed Cisco IP Buzz to accelerate articulation cartage to the about-face in any of
these ways:
In the articulation VLAN, tagged with a layer-2 CoS antecedence value
In the admission VLAN, tagged with a layer-2 CoS antecedence value
In the admission VLAN, untagged (no layer-2 CoS antecedence value)
The about-face can additionally action tagged abstracts cartage (traffic in IEEE 802.1Q or IEEE 802.1p
frame types) from the accessory absorbed to the admission anchorage on the Cisco IP Phone. You can configure
layer-2 admission ports on the about-face to accelerate CDP packets that acquaint the absorbed Cisco
IP Buzz to configure the buzz admission anchorage in one of these modes:
In trusted mode, all cartage accustomed through the admission anchorage on the Cisco IP Buzz passes
through the buzz unchanged.
In untrusted mode, all cartage in IEEE 802.1Q or IEEE 802.1p frames accustomed through the
access anchorage on the Cisco IP Buzz accept a configured layer-2 CoS value. The default
layer-2 CoS amount is 0. Untrusted approach is the default.