问题：

[多选] In the design of a QoS solution， which two factors should be taken into consideration？（）

A .  On congested links， all forms of traffic will require some form of QoS.
B .  All traffic types and requirements should be examined to determine the number of traffic classes required.
C .  In the implementation of link efficiency mechanisms on links that typically transport relatively large packets， header compression will be most efficient.
D .  In the implementation of link efficiency mechanisms on links that typically transport relatively small packets， header compression will be most efficient.
E .  In the implementation of link efficiency mechanisms on links that typically transport relatively small packets， payload compression will be most efficient.
F .  Payload compression provides more available bandwidth and reduces processing delay time.