A Host Interface Architecture and Implementation for ATM Networks

The advent of high speed networks has increased demands on processor architectures. These architectural demands are due to the increase in network bandwidth relative to the speeds of processor components. One important component for a high-performance system is the workstation-to-network host interface . The solution presented in this thesis migrates a carefully selected set of protocol processing functions into hardware. The host interface is highly parallel and all per cell functions are performed by dedicated logic to maximize performance. There is a clean separation between the interface functions, such as segmentation and reassembly, and the interface/host communication. This architecture has been realized in a prototype which connects an IBM RISC System/6000 workstation to a SONET-based ATM network carrying data at the OC-3c1 rate of 155 Mbps

Operating Systems Support for End-to-End Gbps Networking

This paper argues that workstation host interfaces and operating systems are a crucial element in achieving end-to-end Gbps bandwidths for applications in distributed environments. We describe several host interface architectures, discuss the interaction between the interface and host operating system, and report on an ATM host interface built at the University of Pennsylvania. Concurrently designing a host interface and software support allows careful balancing of hardware and software functions. Key ideas include use of buffer management techniques to reduce copying and scheduling data transfers using clocked interrupts. Clocked interrupts also aid with bandwidth allocation. Our interface can deliver a sustained 130 Mbps bandwidth to applications, roughly OC-3c link speed. Ninety-three percent of the host hardware subsystem throughput is delivered to the application with a small measured impact on other applications processing

Experimental Evaluation of an ATM Host Interface

We have previously reported a design for a host interface board intended to connect workstations to ATM networks, and an implementation that was underway. Since then, we have made some modifications to the hardware implementation, and implemented software support. Our prototype connects an IBM RS/6000 to a SONET-based ATM network carrying data at the OC-3c rate of 155Mbps. In this paper, we discuss an experimental evaluation of the interface and supporting software. Our experiments uncovered an unexpected bottleneck in providing high bandwidth to application processes, and we suggest a number of possible improvements to workstation architectures to address this bottleneck

Implementation and Performance of An ATM Host Interface for Workstations

This brief paper outlines our strategies for providing a hardware and software solution to interfacing hosts to high-performance networks. Our prototype implementation connects an IBM RS/6000 to a SONET-based ATM network carrying data at the OC-3c rate of 155Mbps. We have measured application-to-network data rates of up to 130 Mbps

AVATAR -- ATM VideoAudio Transmit and Receive

To facilitate the transport of audio and video data across emerging Asynchronous Transfer Mode (ATM) networks, a simple, low cost, audio/video ATM appliance, the AVATAR, has been developed. This appliance is capable of handling uncompressed bidirectional audio and NTSC video connections. The intended applications for this device include TeleMentoring (a NSF sponsored exploration of distance mentoring), video conferencing, and network monitoring. Our experience has shown that AVATAR is an effective, low cost means of providing multimedia connectivity between sites within the Aurora Gigabit testbed

Event Signaling Within Higher Performance Network Systems

The afterburner ATM link Adapter has allowed us to evaluate three event-signaling schemes: polling, traditional interrupts and the clocked interrupts first investigated in our operating system work in AURORA. The schemes are evaluated in the context of a single-copy TCP/IP stack. The experimental results indicate that clocked interrupts can provide throughput comparable with traditional interrupts for dedicated machines (up to over 144 Mbps, the highest TCP/IP/ATM throughput reported), and better performance when the machines are loaded with an artificial workload. Polling, implemented to be used with an unmodified netperf measurement tool, was competitive for small TCP/IP socket buffer sizes (¡32KB). We concluded that clocked interrupts may be preferable for applications requiring high throughput on systems with heavy processing workloads, such as servers

Leaf trichomes and foliar chemistry mediate defence against glasshouse thrips; Heliothrips haemorrhoidalis (Bouché) in Rhododendron simsii

Herbivore defence mechanisms are a costly diversion of resources away from growth and reproduction. Thus time-limited and tissue specific expression in critical plant parts is more efficient as defined by optimal defence theory. Surprisingly little is known about Rhododendron herbivore defence but it may be mediated by combined chemical and physical mechanisms. Rhododendron simsii Planch. survives cyclic infestations of a leaf-feeding thrips, Heliothrips haemorrhoidalis, which severely damage mature leaves but avoid terminal young leaves suggesting specific, localised defence expression. We examined correlations between the distribution of thrips and feeding damage with density of trichomes and the concentration of the diterpenoid, grayanotoxin I, a compound implicated in but not previously reported to meditate invertebrate defence in Rhododendron. Our data show that as leaves matured the number of thrips and area of feeding damage increased as trichome density and grayanotoxin I concentration decreased, this inverse correlation 10 suggesting trichomes and grayanotoxin I mediate defence in younger leaf tissue. Grayanotoxin I was tested against H. haemorrhoidalis and was toxic to immature life stages and repellent to the adult thrips, reducing numbers of first instars emerging on leaves when applied at ecologically relevant concentrations. This work demonstrates that the pattern of defensive traits in foliage of a species of Rhododendron is key to its ability to tolerate cyclic infestations of a generalist herbivore, effectively conserving vital tissues required for growth and reproduction

Herbivore-Mediated Effects of Glucosinolates on Different Natural Enemies of a Specialist Aphid

The cabbage aphid Brevicoryne brassicae is a specialist herbivore that sequesters glucosinolates from its host plant as a defense against its predators. It is unknown to what extent parasitoids are affected by this sequestration. We investigated herbivore-mediated effects of glucosinolates on the parasitoid wasp Diaeretiella rapae and the predator Episyrphus balteatus. We reared B. brassicae on three ecotypes of Arabidopsis thaliana that differ in glucosinolate content and on one genetically transformed line with modified concentrations of aliphatic glucosinolates. We tested aphid performance and the performance and behavior of both natural enemies. We correlated this with phloem and aphid glucosinolate concentrations and emission of volatiles. Brevicoryne brassicae performance correlated positively with concentrations of both aliphatic and indole glucosinolates in the phloem. Aphids selectively sequestered glucosinolates. Glucosinolate concentration in B. brassicae correlated negatively with performance of the predator, but positively with performance of the parasitoid, possibly because the aphids with the highest glucosinolate concentrations had a higher body weight. Both natural enemies showed a positive performance-preference correlation. The predator preferred the ecotype with the lowest emission of volatile glucosinolate breakdown products in each test combination, whereas the parasitoid wasp preferred the A. thaliana ecotype with the highest emission of these volatiles. The study shows that there are differential herbivore-mediated effects of glucosinolates on a predator and a parasitoid of a specialist aphid that selectively sequesters glucosinolates from its host plant

Flower vs. Leaf Feeding by Pieris brassicae: Glucosinolate-Rich Flower Tissues are Preferred and Sustain Higher Growth Rate

Interactions between butterflies and caterpillars in the genus Pieris and plants in the family Brassicaceae are among the best explored in the field of insect–plant biology. However, we report here for the first time that Pieris brassicae, commonly assumed to be a typical folivore, actually prefers to feed on flowers of three Brassica nigra genotypes rather than on their leaves. First- and second-instar caterpillars were observed to feed primarily on leaves, whereas late second and early third instars migrated via the small leaves of the flower branches to the flower buds and flowers. Once flower feeding began, no further leaf feeding was observed. We investigated growth rates of caterpillars having access exclusively to either leaves of flowering plants or flowers. In addition, we analyzed glucosinolate concentrations in leaves and flowers. Late-second- and early-third-instar P. brassicae caterpillars moved upward into the inflorescences of B. nigra and fed on buds and flowers until the end of the final (fifth) instar, after which they entered into the wandering stage, leaving the plant in search of a pupation site. Flower feeding sustained a significantly higher growth rate than leaf feeding. Flowers contained levels of glucosinolates up to five times higher than those of leaves. Five glucosinolates were identified: the aliphatic sinigrin, the aromatic phenyethylglucosinolate, and three indole glucosinolates: glucobrassicin, 4-methoxyglucobrassicin, and 4-hydroxyglucobrassicin. Tissue type and genotype were the most important factors affecting levels of identified glucosinolates. Sinigrin was by far the most abundant compound in all three genotypes. Sinigrin, 4-hydroxyglucobrassicin, and phenylethylglucosinolate were present at significantly higher levels in flowers than in leaves. In response to caterpillar feeding, sinigrin levels in both leaves and flowers were significantly higher than in undamaged plants, whereas 4-hydroxyglucobrassicin leaf levels were lower. Our results show that feeding on flower tissues, containing higher concentrations of glucosinolates, provides P. brassicae with a nutritional benefit in terms of higher growth rate. This preference appears to be in contrast to published negative effects of volatile glucosinolate breakdown products on the closely related Pieris rapae