A.aggregation congestion occurring at the core layer where the different distribution layer devices feed traffic to the core-layer switches
B.speed mismatches when moving from a low-speed LAN environment to a higher speed WAN environment
C.flapping Ethernet interfaces caused by misconfigured LAN interfaces
D.flapping serial interfaces caused by misconfigured WAN interfaces
E.speed mismatches when moving from a high-speed LAN environment to a lower speed WAN environment

A.over leased lines， use the multilink ppp command to reduce latency and jitter， and to create Distributed Link Fragmentation and interleaving
B.use the service-policy command to attach a traffic flow to an interface on the router
C.use the ip rsvp bandwidth command to set a strict upper limit on the bandwidth NBAR uses， and to guarantee admission of any flows
D.use the policy-map command to define one or more QoS policies （such as shaping， policing， and so on） to apply to traffic defined by a class map
E.use the random-detect dscp command to modify the default minimum and maximum thresholds for the DSCP value
F.use the class-map command to define one or more traffic classes by specifying the criteria by which traffic is classified