Dell PowerConnect 6248 Configuration Guide - Page 37
Voice VLAN, Using Voice VLAN - qos setup
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Voice VLAN Voice VLAN enables switch ports to carry voice traffic with a defined priority in order to enable the separation of voice and data traffic coming onto the port. A primary benefit of using Voice VLAN is to ensure that the sound quality of an IP phone is safeguarded from deteriorating when the data traffic on the port is high. The inherent isolation provided by VLANs ensures that inter-VLAN traffic is under management control and that network attached clients cannot initiate a direct attack on voice components. QoS based on IEEE 802.1P class of service (CoS) uses classification and scheduling to send network traffic from the switch in a predictable manner. The system uses the source MAC address of the traffic traveling through the port to identify the IP phone data flow. IP Phones will use this VLAN. They will obtain their VLAN ID via CDP, DHCP or LLDP-MED. The voice traffic is sent to the switch tagged. The setup protocols (CDP, DHCP, etc.) are not tagged. Using Voice VLAN When an IP phone is connected to the switch, the voice traffic from the phone and the data traffic from the network could potentially deteriorate the voice quality. You can overcome this in multiple ways using different options in Voice VLAN. You can configure the switch to support Voice VLAN on a port that is connecting the VOIP phone. Both of the following methods segregate the voice traffic and the data traffic in order to provide better service to the voice traffic. • 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. By this method, 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 pre-defined VLAN. As a result, both kinds of traffic are segregated in order to provide better service to the voice traffic. Switching Configuration 37