While most of the previous research has focused on providing Quality of Service (QoS) on a per session basis, there is a growing need to also support hierarchical link-sharing, or QoS guarantees for traffic aggregate (such as those belonging to the same organization, service provider, or application family). Supporting QoS for both single sessions and traffic aggregates is difficult as it requires the network to meet multiple QoS requirements at different granularities simultaneously. This problem is exacerbated by the fact that there are no formal models that specify all the requirements.

We have developed an idealized model that is the first to simultaneously capture the requirements of the three important services in an integrated services computer network: guaranteed real-time, adaptive best-effort, and hierarchical link-sharing services. We then designed two hierarchical scheduling algorithms, Hierarchical Packet Fair Queueing (H-PFQ) and Hierarchical Fair Service Curve (H-FSC). H-PFQ is the the first algorithm to simultaneously support all three of real-time, adaptive best-effort, and link-sharing services. H-FSC allows a more flexible resource management than H-PFQ by decoupling the delay and bandwidth allocation. From a conceptual point of view, H-FSC is the first algorithm that goes beyond Fair Queueing and still satisfies all important requirements in integrated services networks. To find out more about and H-PFQ and HFSC's technical advantages, click here.

HFSC, along with a packet classifier and a graphical user interface program has been implemented in both NetBSD 1.2D and FreeBSD 2.2.6. This implementation supports IETF Integrated Services (intserv) service models and RSVP signaling. It also supports most standard CAIRN testbed network hardware. It is currently under testing on CAIRN. Software packages for both NetBSD and FreeBSD are now freely available here.

Several projects are already using HFSC as their QoS engine. To find out more about how HFSC enables QoS in these projects, click here.