The Cisco QoS architecture has evolved quite significantly over time with a strong foundation in (distributed [D]) CAR, (CB) WFQ, PRIQ, custom queuing, WRED, and the new D-WRED. It has evolved into a complete architecture that incorporates the capabilities of Frame Relay (discard eligibility [DE]) and ATM (cell loss priority [CLP]); IP to ATM CoS; in addition to 802.1P/Q marking, IntServ/RSVP and DiffServ, and a strong focus on MPLS-TE and MPLS QoS.
As in most IP stacks, FIFO queuing is the default behavior. Because of lab constraints, I am unable to present labs with 802.1P/Q, DiffServ, and advanced features here.
Recently, AutoQoS was added to the Cisco portfolio, which essentially covers the following in a more proactive way:
QoS classification and marking
QoS configuration and monitoring
QoS congestion avoidance
QoS congestion management
QoS link-efficiency mechanisms
QoS policing and shaping
ATM/Frame Relay QoS
LAN switching QoS