How voice vlans actually work

[GlynnNewey0470]

I understand that a standard access port is not a trunk port, but you can allow two vlans voice and data vlans

Does a voice vlan on an access port basically have its packet all tagged which a voip phone can communicate with as its designed to work with tagged packets only.

And the data vlan basically has untagged traffic, which means all untagged traffic will be associated with the data vlan, as far as the data vlan is concerned its already in the correct vlan so simply does not care about tagged traffic.

I can understand the separation of voice traffic, you would not want a data network to be able to see voice packets for obvious security reasons. Plus I understand you can prioritise packets for voice for qos by separating the vlans. Basically does it work by sending all tagged voice packets first(voice vlan) then send the untagged data packets second(data vlan).

[pieterh]

yes, the access port accepts
- untagged packets for the data vlan
- tagged packets for the voice vlan only
look at this image

the IP phone knows what vlan-id to use in the tag (id is negotiated using CDP or LLDP)
furthermore the switch can be configured to trust the QoS marking from the IP-phone to put voice packets in a priority queue
as the IP-phone acts as a (single port) switch, it can prefer the voice packets over the data packets as outgoing traffic