markb replied on Mon, Jun 15 2009 10:05 AM

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The CS# is a priority level in the DiffServ Code Point (DSCP) system of QoS.  The AF# and EF values are priority levels as well.  There are best practices for each priority level based on throughput and delay needs of different applications.  A use for AF# is to place conforming traffic in for example AF21, if the monitored traffic reaches a threshold (Exceed threshold) you can mark it down to AF22, and then if the traffic reaches another threshold (Violate threshold), you can mark it down to AF23.  Your traffic would then have different drop precedences depending if it hits the queue at AF21, AF22, or AF23.  This type of classification would need to take place as close to the source of the traffic as possible and then the queueing policies would be enforced at  an aggregation point.

EF is Expedited Forwarding - For delay sensitive traffic like voice.  This traffic is usually placed in a priority queue.

CS0   Selector 0 (CS0)     Best Effort
Class Selector 1 (CS1)     Scavenger
AF11                                Bulk Data
AF12 
AF13 
Class Selector 2 (CS2)      Network Management
AF21                                 Transactional Data
AF22 
AF23 
Class Selector 3 (CS3)       Call Signalling
AF31                                  Mission-Critical
AF32 
AF33 
Class Selector 4 (CS4)       Streaming Video
AF41                                   Interactive Video
AF42 
AF43 
Class Selector 5 (CS5) 
Expedited Forwarding (EF) Voice
Class Selector 6 (CS6)        IP Routing