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.

Real-time multimedia transfer through the Internet becomes more difficult when wireless links are in the path, due to the time varying channel capacity, from interference and multipath fading effects which introduce additional stochastic variations beyond the wireline network traffic effects. These wireless variations create problems for existing end-to-end rate adaption using feedback. This paper introduces a framework for cross-layer solutions to the streaming video problem with a focus on graceful degradation under network congestion and/or wireless fading effects without direct coordination between source coder, channel coder, and physical layer modulator. The solution presented includes network transportation and wireless based optimizations and requires little reliance upon end-to-end rate adaption. The suggested method uses progressively coded, leaky prediction source data and physical layer based rate adaption in concert with error tolerant network protocols.

IP version 4 specifies options that extends the basic IP header and also allow new functions to be added to IP without breaking existing implementations. Since options must always be inspected 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 severely increased loss rate.

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

This thesis presents two proposals for improving network layer reaction times and an investigation into the consequences of using IPv4 options. The first proposal, the Selective TRuncating Internetworking Protocol (STRIP), is an augmentation of the IP networking layer. The idea behind STRIP is to expose information related to layered media at the networking layer. Media streams that are divided into different layers (where one layer provides the most basic quality and additional layers provide incremental enhancements to the quality of the media) are placed in the same networking layer protocol data unit (PDU) for transport across the network. Each layer in the PDU is implicitly assigned a priority level, indicating its importance to the media stream. Intermediate routers, on the path of the media stream, can use the exposed layering information to drop parts of the PDU (thereby dropping layers) in response to short term congestion, instead of having to discard an entire packet. By enabling routers to take action as soon as congestion is detected, fast reaction times are made possible. Links with variable throughput, e.g., wireless links, are locations where it is especially desirable to be able to react to short term congestion. The proposal also presents how STRIP could be realized in todays Internet by using IPv4 options. The second proposal is an algorithm that is capable of calculating all backup-paths that are available by simply forwarding packets to directly connected neighbors in the case that a directly connected neighbor fails. The algorithm allows backup-paths to be calculated in advance, which can be used as soon as a router failure is detected. Providing that the failure detection mechanism is fast, router failures can be circumvented very rapidly. The algorithm is compared to a brute force approach and shown to be an order of magnitude faster for the most common network topologies. The investigation of IPv4 options focuses on the implications of their use to implement networking proposals. A widely held belief in the Internet community is that the use of IPv4 options can result in increased loss rates, delays and jitter. Because of the severe implications of this supposition and because there did not seem to exist any actual measurements confirming the claim, it was decided that an investigation should be performed. The result of the investigation shows that packets carrying IP options are indeed subjected to an increase in loss rates, delays and jitter, compared to packets without options. The increase in delay and in jitter are, however, probably not so severe as to rule out the use of options. Unfortunately, the increase in loss rates were found to be very high, definitely raising concerns on the appropriateness of using IPv4 options in networking proposals.

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