Can you enlighten me about type of service in IPv4 and Differentiated Service Code Point (DSCP) in IPv6 as to what extend they contribute to Quality of Service in IP networks and how they contribute to the Differentiated Service mechanisms?
In a nutshell, both are used to set a priority within the packets so that switches and routers can process the traffic at various priorities. For instance if you set the QoS (quality of service which corresponds to the first bit of the type of service) bit to 5 (high priority) data packets set to 0 – routine, get processed and queued while allowing the higher priority voice packets to process. QoS is a layer 2 mechanism while diffserve is a layer 3 mechanism.
Here is a link to a good article that may answer some more questions for you.