To support proper delivery of voice traffic in a hierarchical switched network, follow several QoS rules of thumb. See the basic network diagram in Figure 14-1.
- A QoS trust boundary should be established as close to the end devices (at the access layer) as possible.
- Let the IP Phone handle the trust boundary for attached PCs; the IP Phone should be trusted.
- PCs running Cisco SoftPhone should be untrusted. Instead, the inbound voice traffic should be classified and the CoS and differentiated services code point (DSCP) values marked.
- Normal PCs with no voice capability should be untrusted (CoS and type of service [ToS] set to 0).
- On Catalyst 6000 switches, port trust can be VLAN-based and applied to the voice VLAN ...