The third queuing discipline supported by pfSense is Hierarchical Fair Service Curve (HFSC). An HFSC can be thought of as a form of bandwidth allocation in which guarantees are made about latency. An HFSC queue is defined by a nonlinear curve with two parts. The first part, m1, determines the amount of bandwidth the queue gets up to p milliseconds. After p milliseconds, the second part of the curve (m2) determines the behavior of the queue. This is the amount of bandwidth guaranteed to the queue.
To illustrate HFSC, imagine two services competing for bandwidth: a VoIP connection and a file download. Assume a linear service curve such that the VoIP connection requires that a packet be sent every 30 ms, while ...
