Lars Eggert

Application-level differentiated services for Web servers

The current World Wide Web service model treats all requests equivalently, both while being processed by servers and while being transmitted over the network. For some uses, such as Web prefetching or multiple priority schemes, different levels of service are desirable. This paper presents three simple, server‐side, application‐level mechanisms (limiting process pool size, lowering process priorities, limiting transmission rate) to provide two different levels of Web service (regular and low priority). We evaluated the performance of these mechanisms under combinations of two foreground workloads (light and heavy) and two levels of available network bandwidth (10 Mb/s and 100 Mb/s). Our experiments show that even with background traffic sufficient to saturate the network, foreground performance is reduced by at most 4–17%. Thus, our user‐level mechanisms can effectively provide different service classes even in the absence of operating system and network support.

A Node Identity Internetworking Architecture

The Internet consists of independent networks that belong to different administrative domains and vary in scope from personal area networks, private home networks, corporate networks to ISP and global operator networks. These networks may employ different technologies, communications mediums, addressing realms and may have widely different capabilities. The coming years will add a significant level of dynamic behavior, such as mobile nodes and moving networks, which the Internet must support. At the same time, there is a need to address the increasing levels of harmful traffic and denial-of-service attacks. The existing Internet architecture does not support dynamic behavior or secure communication to a sufficient degree. This paper outlines a node-identity-based internetworking architecture that allows heterogeneous networks to work together without loss of functionality. Some of techniques employed in this architecture include reliance on cryptographic node identifiers, identity routers and localized addressing realms.

Effects of ensemble-TCP

TCP currently recalculates the state of each connection from a fixed set of initial parameters; this recalculation occurs over several round trips, during which the connection can be less than efficient. TCP control block sharing is a technique for reusing information among connections in series and aggregating it among connections in parallel. This paper explores the design space of a modified TCP stack that utilizes these two ideas, and one possible design (E-TCP) is presented in detail. E-TCP has been designed so that the network transmission behavior of group of parallel E-TCP connections closely resembles that of a single TCP/Reno connection. Simulated web accesses using HTTP/1.0 over E-TCP show a significant performance improvement compared to TCP/Reno connection bundles. This paper is first to evaluate performance using four different intra-ensemble schedulers for different workloads. In one scenario simulating a common case, E-TCP is 4-75% faster than Reno for transmitting the HTML parts of various pages, and 17-61% faster transmitting the whole pages. In the same scenario, reusing cached state speeds up repeated E-TCP page accesses by 17-53% for the HTML parts and 10-28% for the whole pages, compared to the initial access. E-TCP can also be integrated with other proposed TCP extensions (such as TCP/Vegas or TCP/SACK), to further improve performance.

Protocol enhancements for intermittently connected hosts

Internet users are increasingly mobile. Their hosts are often only intermittently connected to the Internet, due to using multiple access networks, gaps in wireless coverage or explicit user choice. When such hosts communicate using the current Internet protocols, intermittent connectivity can significantly decrease performance and even cause connections to fail altogether. This paper experimentally measures the behavior of Internet communication across a dynamically changing, intermittently connected path. An analysis of the experimental results finds that address changes together with transport-layer timeout and retransmission behaviors are the main limiting factors. Based on these experimental results, this paper proposes a solution that combines the Host Identity Protocol (HIP) with two new protocol enhancements, the TCP User Timeout Option and the TCP Retransmission Trigger. Detailed experiments with HIP and a prototype implementation of these protocol enhancements show that they tolerate address changes and arbitrary-length disconnections while significantly increasing performance under intermittent connectivity to within 86-96% of a scenario with constant connectivity.

Idletime scheduling with preemption intervals

This paper presents the idletime scheduler; a generic, kernel-level mechanism for using idle resource capacity in the background without slowing down concurrent foreground use. Many operating systems fail to support transparent background use and concurrent foreground performance can decrease by 50% or more. The idletime scheduler minimizes this interference by partially relaxing the work conservation principle during preemption intervals, during which it serves no background requests even if the resource is idle. The length of preemption intervals is a controlling parameter of the scheduler: short intervals aggressively utilize idle capacity; long intervals reduce the impact of background use on foreground performance. Unlike existing approaches to establish prioritized resource use, idletime scheduling requires only localized modifications to a limited number of system schedulers. In experiments, a FreeBSD implementation for idletime network scheduling maintains over 90% of foreground TCP throughput, while allowing concurrent, high-rate UDP background flows to consume up to 80% of remaining link capacity. A FreeBSD disk scheduler implementation maintains 80% of foreground read performance, while enabling concurrent background operations to reach 70% throughput.

An experimental study of home gateway characteristics

Many residential and small business users connect to the Internet via home gateways, such as DSL and cable modems. The characteristics of these devices heavily influence the quality and performance of the Internet service that these users receive. Anecdotal evidence suggests that an extremely diverse set of behaviors exists in the deployed base, forcing application developers to design for the lowest common denominator. This paper experimentally analyzes some characteristics of a substantial number of different home gateways: binding timeouts, queuing delays, throughput, protocol support and others.

An Experimental Evaluation of Voice Quality Over the Datagram Congestion Control Protocol

Most Internet telephony applications currently use either TCP or UDP to carry their voice-over-IP (VoIP) traffic. This choice can be problematic, because TCP is not well suited for interactive traffic and UDP is unresponsive to congestion. The IETF has recently standardized the new Datagram Congestion Control Protocol (DCCP). DCCP has been designed to carry media traffic and is congestion-controlled. This paper experimentally evaluates the voice quality that Internet telephony calls achieve over prototype implementations of basic DCCP and several DCCP variants, under different network conditions and with different codecs. It finds that the currently-specified DCCP variants perform less well than expected when compared to UDP and TCP. Based on an analysis of these results, the paper suggests several improvements to DCCP and experimentally validates that a prototype implementation of these modifications can significantly increase voice quality.

Ambient networks: bridging heterogeneous network domains

Providing end-to-end communication in heterogeneous internetworking environments is a challenge. Two fundamental problems are bridging between different internetworking technologies and hiding of network complexity and differences from both applications and application developers. This paper presents abstraction and naming mechanisms that address these challenges in the Ambient Networks project. Connectivity abstractions hide the differences of heterogeneous internetworking technologies and enable applications to operate across them. A common naming framework enables end-to-end communication across otherwise independent internetworks and supports advanced networking capabilities, such as indirection or delegation, through dynamic bindings between named entities

Analysis of Path Characteristics and Transport Protocol Design in Vehicular Ad Hoc Networks

Vehicular ad hoc networks (VANETs) enable new applications by providing self-organizing vehicle-to-vehicle and vehicle-to-roadside communication. Some of these applications require reliable, in-order data delivery across end-to-end connections. The performance of a vehicular transport protocol (VTP) that provides such a service depends on its ability to adapt quickly to the varying path characteristics of highly dynamic environments. This paper studies path characteristics of VANETs in highway scenarios. An analytical evaluation derives upper bounds on the expected connectivity and disruption duration. Simulations validate these results and study further metrics, such as packet loss, packet reordering and round trip times. The paper also briefly outlines a preliminary VTP design that incorporates these analytical results

A global X-bone for network experiments

A global Internet overlay testbed is being deployed to support the distributed, shared use of resources for network research. The Global X-Bone (GX-Bone) augments the X-Bone software system, enhancing its coordination mechanisms to support deployment of local overlays to world-wide, shared infrastructure. The GX-Bone is based on the X-Bones Virtual Internet Architecture which extends the Internet for both concurrent, parallel and recursive overlays and provides decentralized, automated deployment and management. GX-Bone supports host visualization through the NetFS file system, granting individual users compartmentalized access and control of host and router configuration and the DataRouter extension to IP loose source routing that supports application control of network-layer forwarding. GX-Bone can be installed on user-modified kernels, uniquely supporting both conventional kernel-level protocol development and coordinated global infrastructure sharing.