Voice VLAN is used to isolate voice traffic for two main reasons:
- Security. Nowadays such software as Wireshark or Voice Over Misconfigured Internet Telephones (VOMIT) makes it possible to pick voice packets out, process them and compile the whole conversation into an audio file with a WAV extension. So to prevent eavesdropping one has to isolate both types of traffic from each other.
- QoS. Used for voice traffic prioritization among others.
switchport mode access
switchport access vlan 10
switchport voice vlan 45