Quality Issues in Internet Packet Forwarding

This thesis addresses quality issues in Internet Protocol (IP) packet forwarding. In IP networks, queue mechanisms and scheduling can be used to construct multiple forwarding behaviors. Thereby, both relative and independent services can be offered to Internet users. Independent services offer forwarding qualities known beforehand. Users are assumed to explicitly request admission to an independent service from their network provider. With relative services, users switch between these services to find one that provides an appealing balance between forwarding quality and cost. The thesis makes contributions to three research areas related to forwarding quality in IP networks; differentiating forwarding mechanisms, admission control for differentiated services, and forwarding quality in radio networks carrying Internet traffic. It contributes to the first research area with definitions of three recommendations related to offering loss-rate differentiation (i.e., multiple drop precedence levels). These recommendations are; (1) the total forwarding quality at congested links should not be degraded due to actions taken to create loss-rate differentiation, (2) traffic at high drop precedence levels should always be given a useful share of available forwarding resources, and (3) users should be able to predict the change in loss-rates when switching between drop precedence levels. We specify and evaluate properties of queue mechanisms following these recommendations. Also, as a contribution to the first research area, a new set of forwarding behaviors is specified and analyzed. These forwarding behaviors are suitable for rate-adaptive and delaysensitive applications with limited loss-tolerance. Applications needing loss-free forwarding of specific packets can be said to have limited loss tolerance. We define and evaluate a scheduling mechanism creating these forwarding behaviors that can be implemented efficiently. The contribution to the second research area is a mechanism for admission control giving assurances on loss-rates to rate varying applications is defined. With this mechanism, dynamic per-link admission thresholds are used to limit committed aggregate rates. To allow for high link utilization through statistical multiplexing we specify a method to adjust these thresholds using low impact traffic monitoring mechanisms commonly available in legacy routers. In radio networks carrying IP traffic, radio transmissions can be scheduled differently to balance spectrum utilization and the forwarding quality provided. Also, parameters settings can be used to optimize the forwarding quality in radio networks for certain transport protocols and applications. This thesis analyses delay spikes experienced by IP traffic in cellular radio networks. We evaluate two different radio-block scheduling mechanisms’ impact on two versions of the Transmission Control Protocol (TCP) (i.e., TCP Sack and TCP Eifel). The evaluation contributes to the third research area by revealing basic dependencies between scheduling, interference, and congestion control mechanisms implemented by TCP. Finally, the thesis contributes to the third research area by proposing extensions to the Internet architecture for inter-layer communication. These extensions allow applications and transport protocols to exchange information with radio link layers. Such information exchange can be used to improve the forwarding quality and to customize data and transport features for current radio conditions. Quality Issues in Internet Packet Forwarding v