Router mechanisms designed to achieve fair bandwidth allocations, like Fair Queueing, have many desirable properties for congestion control in the Internet. However, such mechanisms usually need to maintain state, manage buffers, and/or perform packet scheduling on a per flow basis, and this complexity may prevent them from being cost-effectively implemented and widely deployed. In this paper, we propose an architecture that significantly reduces this implementation complexity yet still achieves approximately fair bandwidth allocations. We apply this approach to an island of routers -- that is, a contiguous region of the network -- and we distinguish between edge routers and core routers. Edge routers maintain per flow state; they estimate the incoming rate of each flow and insert a label into each packet header based on this estimate. Core routers maintain no per flow state; they use FIFO packet scheduling augmented by a probabilistic dropping algorithm that uses the packet labels an...

We consider the transmission of variable bit rate (VBR) video over a network offering a guaranteed service such as ATM VBR or the guaranteed service of the IETF. The guaranteed service requires that the flow accepted by the network has to be conforming with a traffic envelope #; in return, it receives a service guarantee expressed by a network service curve #. Functions # and # are derived from the parameters used for setting up the reservation, for example, from the T-SPEC and R-SPEC fields used with the Resource Reservation Protocol (RSVP). In order to satisfy the traffic envelope constraint, the output of the encoder is fed to a smoother, possibly with some look-ahead. The resulting stream is transported by the network; at the destination, the decoder waits for an initial playback delay and reads the stream from the receive buffer. We consider the problem of whether there exists one optimal strategy at the smoother which minimizes the playback delay and the receive buffer size, given the traffic envelope # and the service curve #. We show that there does exist such an optimal smoothing, and give an explicit representation for it. We also obtain a simple expression for the smallest playback delay and playback buffer size which can be achieved over all possible smoothing and playback strategies. We show that the computation of optimal smoothing and minimum playback delay do not depend on the past. We show that separate delay equalization is optimal in the CBR case, but not otherwise. We also apply the theory to the analysis of which T-SPEC should be requested by a source-destination pair, given some playback delay and buffer constraint, and given the path characteristics advertised in RSVP PATH messages.

Bounding performance characteristics in communication networks is an important and interesting issue. In this study we assume uncertainty about the way di erent ows in a network are multiplexed, we even drop the common FIFO assumption. Under so-called blind multiplexing we derive new bounds for the tractable, yet non-trivial case of feed-forward networks. This is accomplished for pragmatic, but general tra c and server models using network calculus. In particular, we derive an end-to-end service curve for a ow of interest under blind multiplexing, establishing what we call the pay multiplexing only once principle. We specify the algorithms necessary to apply this result in a network of blind multiplexing nodes. Since these algorithms may have prohibitive computational costs, we present strategies to reduce the computational e ort in a controlled manner such that the quality of the bounds is a ected as little as possible. Finally we present some numerical results from a network calculus tool we developed and compare our bounds against the best known bounds for networks of blind multiplexing nodes.

In this paper we describe the design, implementation, and analytical background of the DISCO Network Calculator. The DISCO Network Calculator is an open-source toolbox written in Java which we developed for worst-case analyses based on network calculus. To our knowledge it is the first of its kind. It allows to do network analyses regarding performance characteristics such as delay and backlog bounds for piecewise linear arrival and service curves. We illustrate the tool's usefulness by two comprehensive example applications.