A PHB is applied to each BA inside the network. The boundary router is positioned at the edge of a DiffServ-capable network. The functions defined for the boundary router can be performed on a router, firewall, or even a host. Interior nodes can be core switches or routers that provide the PHB based on the DSCP bits contained in the DS-field. Figure 3 illustrates the DiffServ boundary and interior functions.
Packets enter the network through an ingress boundary router.
The role of the traffic meter is to measure the packet's conformance with a traffic profile agreed upon by the network provider and the customer. To minimize jitter and delay, packets must spend little or no time in router queues. The core routers in Figure 3 contains a simple BA classifier that determines the PHB to be applied to the packet. All packets belonging to a BA are handled the same way. Again, the PHB is an externally observable behavior performed on each node that is realized through internal queue management and scheduling techniques.