Auto-QoS

Auto-QoS
Obviously, implementing QoS can be an administrative headache. Some configurations have
the potential to affect application delivery across a wide spectrum of the network, and without
practical skills and experience it’s easy to make mistakes. To help administrators build QoSbased
networks with the minimum of effort, Cisco has created something called auto-QoS.
Auto-QoS can be used to simplify the deployment of QoS features. Auto-QoS makes certain
assumptions about the network design, allowing the switch to prioritize different traffic flows
and use the output queues appropriately instead of just using the default QoS behavior of best
efforts service from a single queue. Auto-QoS uses the input packet label and traffic type to
automatically classify traffic. The switch then uses this classification to place traffic in the
appropriate output queue.
One of the main features of auto-QoS is the ability of the switch to identify ports that
have IP telephones attached to them and allocate sufficient buffer space to afford the VoIP
(Voice over IP) calls the correct QoS. This does not just apply to the ports with the IP phones
connected, but also to uplinks that carry the VoIP calls to the next switch. This process is
called trust.
Trust allows for ports that may carry VoIP traffic (but not actually have IP phones directly
connected) to recognize that a packet marked as carrying such a service must be afforded the
same QoS as if it were directly connected, and therefore proven to be VoIP. Trust is configured
across a QoS domain. Packets are marked only at the ingress to the domain and trusted from
there on, obviating the need to mark again at every switch or router.
Trust will be pretty important in the future, when all networks start to use
QoS. Obviously, QoS is not going to be free, and ISPs will probably charge
more for better QoS on the Internet. It follows that when an arriving packet
demands a better QoS because of some bits set in an IP header, we should be
certain that we are prepared to agree to those demands; otherwise the system
would be open to abuse. Disreputable users would be able to manipulate
the DSCP code bits to create higher priorities for web browsing, for example.