An order-theoretic characterization of the Howard-Bachmann-hierarchy

In this article we provide an intrinsic characterization of the famous Howard-Bachmann ordinal in terms of a natural well-partial-ordering by showing that this ordinal can be realized as a maximal order type of a class of generalized trees with respect to a homeomorphic embeddability relation. We use our calculations to draw some conclusions about some corresponding subsystems of second order arithmetic. All these subsystems deal with versions of light-face Π₁¹-comprehension

Multipath routing and multiple description coding in ad-hoc networks : a simulation study

The nature of wireless multihop ad-hoc networks makes it a challenge to offer connections of an assured quality. In order to improve the performance of such networks, multipath routing in combination with Multiple Description Coding (MDC) has been proposed. By splitting up streams of multimedia traffic into several substreams (called descriptions), by sending these substreams along different paths from the source to the destination, and by reassembling them again at the destination, the quality of the received stream may be improved as compared to the single-description, single-path case. In this paper we present a simulation study of the combination of MDC and multipath routing from a network perspective with a realistic medium access control protocol (IEEE 802.11) and a widely used routing protocol (Dynamic Source Routing with our own multipath extensions). Our simulations show that for most of the cases considered, the combination of multipath routing and MDC does not perform better than single-path routing and a single description in IEEE 802.11-based networks