Routers SHOULD implement precedence-ordered queue service. Precedence-ordered queue service means that when a packet is selected for output on a (logical) link, the packet of highest precedence that has been queued for that link is sent. Routers that implement precedence-ordered queue service MUST also have a configuration option to suppress precedence-ordered queue service in the Internet Layer.
Any router MAY implement other policy-based throughput management procedures that result in other than strict precedence ordering, but it MUST be configurable to suppress them (i.e., use strict ordering).
As detailed in Section [5.3.6], routers that implement precedence- ordered queue service discard low precedence packets before discarding high precedence packets for congestion control purposes. Preemption (interruption of processing or transmission of a packet) is not envisioned as a function of the Internet Layer. Some protocols at other layers may provide preemption features.