Hi Sze Jie K,
Let me jump in on this. You are using a 3560 or 3750?
Once you enable QoS, all CoS/DSCP values get assigned to 4 different queues. You can’t change or disable these. If you want to mimic something where only voice traffic gets priorited then you could configure something like this:
Q1: 10% of bandwidth
Q2: 80% of bandwidth
Q3/Q4: each 5% of bandwidth
You can assign the CoS/DSCP values that you use for Voice to Q1 and everything else to Q2. It’s a pain to configure QoS on these switches as it affects all your traffic. It’s not as easy as on a router when you can configure only the priority queue for voice and let everything else be forwarded like it was before QoS.
Rene