Improving the robustness of today's intra-domain link-state networks is of increasing importance. This is because it is becoming commonplace for such networks to carry telephony, on-demand video and other kinds of real-time traffic. Since user requirements on real-time traffic are exacting, it is essential that the network is able to respond rapidly to network errors. A way of reaching fast reaction times in response to network errors is to precompute fail-over paths that can be utilized immediately when an error is detected. The fail-over path is thereafter in use until the network has converged, handling traffic that would otherwise have been lost due to the error. During convergence (when new paths are calculated) there is a caveat that needs to be avoided -the formation of temporary loops. Temporary loops can form naturally during convergence in link-state networks and can unfortunately prevent traffic from reaching a fail-over path. Traffic can therefore be lost even though a fail-over path is in place. We present an algorithm that can be used in conjunction with link-state routing, to ensure that temporary loops do not form during convergence. The algorithm improves on previous loop-free algorithms for link-state routing by reducing the number of state transitions necessary before a router can update its routing table to a new, guaranteed to exist, path for a wide variety of topological configurations.

IP version 4 specifies options that extend the basic IP header and also allow new functions to be added to IP without breaking existing implementations. Since options must always be inspected at routers, it is generally believed that routers prioritize ordinary packets over packets carrying options in a way that significantly impacts the performance of options. This article presents an experiment based on end-to-end probing using UDP packets, capturing the performance penalties associated with IPv4 options. Analysis of experiment results quantifies the impact of IPv4 options on forwarding performance in terms of delay, jitter and loss rate. From the analysis it can be concluded that there is a slight increase in delay and jitter and a severe increase in loss rate.

Godkänd; 2004; 20061127 (ysko)

Many emerging real-time applications generate layered data streams, which can be used effectively to adapt multicast real-time transmissions to heterogeneous bandwidth environments. However, these applications have not changed with regard to being sensitive to transient congestion and cannot wait a full round-trip time for sender-initiated adaptation. In this paper we propose the selective truncating internetwork protocol (STRIP) supporting layered data transfer, and capable of handling congestion at a finer level of granularity by truncating packets, i.e., stripping off less important data. STRIP inter-operates with the traditional IP infrastructure and can be introduced in a step-by-step fashion, starting where the benefits are obvious, for example with routers which are connected to bandwidth constrained links and which have a surplus of processing capacity. We describe the design and architecture of STRIP and compare it with solutions for differentiated forwarding on a per-packet basis. STRIP provides a simple mechanism that can meet the demands for real-time flows effectively by supporting low delay forwarding, avoiding data-unit reordering, and supporting various drop priorities at the same time.