Hi
qos basically manages the bandwidth available during congestion and it doesnt create bandwidth.
The config differs based on the requirements of the customers and also the bandwidth they have.
There are 5 different steps in achieving the same which begins with classification, marking, policing, shaping and queueing,
Classification is where you identify the traffic pattern based on the TCP ports or ACLS or using NBAR.
Marking again done with DSCP or IP Precedence values in normal ip backbone and using MPLS EXP bits in the MPLS backbone.
this is where you tag the importance to the traffic pattern which you have identified in the previous step and give the kinda priority or bandwidth assurance to them.
Policing basically to monitor the traffic flow and drop or remark them with defered dscp values once it exceeds the confirmed or viloated value.
shaping is the next thing which doesnt drop but put them on buffer and send them during non congestion so your traffic utilisation on your link will be uniform irrespective of usage you have.
ofcourse i would suggest to go thru this link to have more info about qos..
http://cisco.com/en/US/tech/tk543/tsd_technology_support_category_home.html
regds
