You can use the auto-QoS feature to simplify the deployment of existing QoS features. Auto-QoS makes assumptions about the network design, and as a result, the switch can prioritize different traffic flows and appropriately use the egress queues instead of using the default QoS behavior (the switch offers best-effort service to each packet regardless of the packet contents or size and sends it from a single queue).
When you enable auto-QoS, it automatically classifies traffic based on the traffic type and ingress packet label. The switch uses the resulting classification to choose the appropriate egress queue.
You use auto-QoS commands to identify ports connected to Cisco IP Phones and to devices running the Cisco SoftPhone application. . You also use the commands to identify ports that receive trusted traffic through an uplink. Auto-QoS then performs these functions:
•Detects the presence or absence of IP phones
•Configures QoS classification
•Configures egress queues
That tells me that auto-qos is useful for voip since vopi packet have DSCP and CoS value filled out. It would benefit the data if the data traffic coming in already have CoS or DSCP values. The uato-qos would use the CoS or DSCP value from the data packet to treat them accordingly. Auto-QoS is a macro command that enables cos mapping to the the appropriate queues.
