Eclipse/BSD's network output link scheduler uses the hierarchical WF2Q (Worst-case Fair Weighted Fair Queueing) algorithm . This algorithm is similar to an earlier GPS approximation, WFQ (Weighted Fair Queueing) . However, unlike WFQ, WF2Q does not schedule a packet until it is eligible, i.e., its transmission would have started under GPS. Consequently, WF2Q has optimal worst-case fair index bound, making it a good choice for a hierarchical scheduler .
Note that neither YFQ nor WF2Q could be used for CPU scheduling, since they assume that the time necessary to process a request can be estimated and they never preempt a request.