Improving network layer reaction times

Abstract: 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.