I'm working through the IPexperts Lab2 for the CCIE Wireless - trying to reverse engineer the solutions to the questions and understand the subjects where I'm lacking. Namely QoS.
I was digging around trying to find the reason why the solution for section 2.8 bullet point number two was to use the command 'mls qos trust ip-precedence' for all the connections between the core switches. The bullet point asks you to ensure that the layer 3 QoS markings are trusted between the switches, and that you trust the 3 most significant bits of the DiffServ field in the IP packet.
I found this explanation for the difference between 'mls qos trust dscp' and 'mls qos trust ip-precedence'. DSCP is the most significant 6 bits of 8-bit service-type field, where IP-Precedence refers to the most significant 3 bits of 8-bit service-type field.
This picture shows this breakdown in a little better detail.