Hi Muhammed,
if i have correctly understood your question you will possibly find useful these couple of answers:
a) the default for every interface is FIFO (first in first out) - as to say the firs to come is the first processed
b) you can define a subinterface with a stronger priority than others but this is not the purpose of QoS
find attached a very nice documentation about the commands you need to use to achieve your goals and specifically for your purpose i would like t sugest you to check the "match" command to fit the needs of your networks.
Take Care
Alessio
