Cisco IOS QoS and Queuing Architectures

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

  • QoS signaling

  • ATM/Frame Relay QoS

  • LAN switching QoS