"If there is no congestion, then the policy-map does not come to effect. Would this be a correct statemet ? "
Yes, with regards to basic CBWFQ queuing. Not true if you were also using the CBWFQ policy to mark/police/shape packets (NB: as not done in your policy-map example).
"that the service-policy only becomes in effect when there is congestion in the link ?"
Keeping in mind above answer, logically yes, although even for basic policy queuing (such as your example) actually there's often an interface hardware queue or buffer, that when it overflows, the overflow packets are placed into the CBWFQ queue(s). I.e. some congestion might not derive benefit of your policy queuing. (NB: often interface command to adjust hardware queue/buffer size. Later IOSs are supposed to size default better.)
Also, policy maps can be used to manage queue congestion when the physical link isn't congested, such as for a subinterface or VC and/or under a shaper.
Hi everyone, I would like to thank you in advance for any help you can provide a newcomer like myself!
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