The Assured Forwarding (AF) service of the IETF DiffServ architecture provides a qualitative service differentiation between classes of traffic, in the sense that a low-priority class experiences higher loss rates and higher delays than a high-priority class. However, the AF service does not quantify the difference in the service given to classes. In an effort to strengthen the service guarantees of the AF service, we propose a Quantitative Assured Forwarding service with absolute and proportional differentiation of loss, service rates, and packet delays. We present a feedback-based algorithm which enforces the desired class-level differentiation on a per-hop basis, without the need for admission control or signaling. Measurement results from a testbed of FreeBSD PC-routers on a 100 Mbps Ethernet network show the effectiveness of the proposed service, and indicate that our implementation is suitable for networks with high data rates.

A novel algorithm for buffer management and rate allocation is presented for providing loss and delay differentiation for traffic classes at a network router. The algorithm, called JoBS, provides delay and loss differentiation independently at each node, without assuming admission control or policing. Contrary to most existing algorithms, scheduling and buffer management decisions are performed in a single step. Both relative

ii Acknowledgements iv Acronyms xiii 1

In this dissertation, we present a novel service architecture for the Internet, which reconciles application demand for strong service guarantees with the need for low computational overhead in network routers. The main contribution of this dissertation is the definition and realization of a new service, called Quantitative Assured Forwarding, which can offer absolute and relative differentiation of loss, service rates, and packet delays to classes of traffic. We devise and analyze mechanisms that implement the proposed service, and demonstrate the effectiveness of the approach through analysis, simulation and measurement experiments in a testbed network. To enable

Class-based service differentiation can be realized without resource reservation, admission control and traffic policing. However, the resulting service guarantees are only relative, in the sense that guarantees given to a flow class at any time are expressed with reference to the service given to other flow classes. While it is, in principle, not feasible to provision for absolute guarantees (i.e., to assure lower bounds on service metrics at all times) without admission control and/or traffic policing, we will show in this paper that such a service can be reasonably well emulated using adaptive rate allocation and dropping mechanisms at the link schedulers of routers. We name the resulting type of guarantees best-effort bounds. We propose mechanisms for link schedulers of routers that achieve these and other guarantees by adjusting the drop rates and the service rate allocations of traffic classes to current load conditions.