Dell PowerConnect 7048P User Manual - Page 578

The Voice VLAN feature can be enabled on a per-port basis. This feature supports a configurable voice VLAN DSCP value. This value is later retrieved by LLDP when the LLDPDU is transmitted, if LLDP has been enabled on the port and the required TLV is configured for the port. Identifying Voice Traffic Some VoIP phones contain full support for IEEE 802.1X. When these phones are connected to a port that uses 802.1X port-based authentication, these phones authenticate and receive their VLAN information from LLDP-MED. However, if a VoIP phone has limited support for 802.1X authentication it might try to authenticate and fail. A phone with no 802.1X support would not attempt to authenticate at all. Instead of placing these phones on an unauthenticated or guest VLAN, the switch can automatically direct the VoIP traffic to the Voice VLAN without manual configuration. The switch identifies the device as a VoIP phone by one of the following protocols: • Cisco Discovery Protocol (CDP) or Industry Standard Discovery Protocol (ISDP) for Cisco VoIP phones • DHCP for Avaya VoIP phones • LLDP-MED for most other VoIP phones NOTE: By default, ISDP is enabled globally and per-interface on the switch. LLDP-MED is disabled on each interface by default. Port-based authentication using 802.1X is also disabled on each port by default. After the VoIP phone receives its VLAN information, all traffic is tagged with the VLAN ID of the Voice VLAN. The phone is considered to be authorized to send traffic but not necessarily authenticated. Segregating Traffic with the 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. 578 Configuring VLANs