Voice VLAN

In this article we will discuss Voice VLAN, will make brief discussion on Voice VLAN, last article we discuss about Analog Modems.

The voice VLAN is an ingenious feature that enables access ports to carry voice traffic from an IP phone. Cisco IP phones connect to the IP network using Ethernet to send Voice over IP (VoIP) packets.

The voice VLAN feature is disabled by default. When the voice VLAN feature is enabled, all untagged traffic is sent according to the default CoS priority of the port. The CoS value is not trusted for IEEE 802.1p or IEEE 802.1Q tagged traffic.

The voice VLAN feature enables access ports to carry IP voice traffic from an IP phone. Port 1 connects to the switch or other voice-over-IP (VoIP) device. Port 2 is an internal 10/100 interface that carries the IP Phone traffic. Usually, IP phones sit next to a computer on the same desk. They require the same UTP cables as computers and also use Ethernet. If we want to connect them to a switch, we have two options.

The voice VLAN feature is supported only on access ports. Voice VLAN permits the switch to accept tagged traffic on an access (normally untagged) link. CDP is used to negotiate the voice VLAN between the phone and the network switch (the switch signals the phone; this voice VLAN is a separate TLV in the CDP standard).

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