Showing papers by "Jon Crowcroft published in 2001"

PGM Reliable Transport Protocol Specification

Abstract: Pragmatic General Multicast (PGM) is a reliable multicast transport protocol for applications that require ordered or unordered, duplicate-free, multicast data delivery from multiple sources to multiple receivers. PGM guarantees that a receiver in the group either receives all data packets from transmissions and repairs, or is able to detect unrecoverable data packet loss. PGM is

Congestion control mechanisms and the best effort service model

Abstract: In the last few years there has been considerable research toward extending the Internet architecture to provide quality of service guarantees for the emerging real-time multimedia applications. QoS provision is a rather controversial endeavour. At one end of the spectrum there were proposals for reservations and per-flow state in the routers. These models did not flourish due to the network's heterogeneity the complexity of the mechanisms involved, and scalability problems. At the other end, proposals advocating that an overprovisioned best effort network will solve all the problems are not quite convincing either. The authors believe that more control is clearly needed for protecting best effort service. An important requirement is to prevent congestion collapse, keep congestion levels low, and guarantee fairness. Appropriate control structures in a best effort service network could even be used for introducing differentiation. This could be achieved without sacrificing the best effort nature of the Internet or stressing its architecture beyond its limits and original design principles. We revisit the best effort service model and the problem of congestion while focusing on the importance of cooperative resource sharing to the Internet's success, and review the congestion control principles and mechanisms which facilitate Internet resource sharing.

Networked Group Communication

Abstract: This book constitutes the refereed proceedings of the Third International COST264 Workshop on Networked Group Communication, NGC 2001, held in London, UK, in ...

Congestion pricing. Paying your way in communication networks

Abstract: Network congestion is a fundamental problem facing Internet users today. A network where users are selfish, and thus reluctant to defer to other users, may result in the famous "tragedy of the commons", where, in the absence of controls, a shared resource is overconsumed by individuals who consider only their personal costs and not the cost to society as a whole. In terms of the Internet, the "tragedy" could be viewed as congestive collapse, resulting from overconsumption of the shared network resource. It is important to distinguish congestion pricing from other forms of network pricing. Charging network users for the congestion they cause can lead to more efficient network utilization by forcing them to take social costs into account. In a congestion-pricing framework, the congestion charge would replace usage and QoS charges. Users would pay their ISPs a subscription charge to cover fixed costs and a congestion charge only when appropriate. This pricing scheme is feasible because, in the absence of congestion, the marginal cost of a network link is practically zero. Congestion pricing can also benefit network operators. By indicating the level of congestion and the user tolerance of it in their networks, congestion pricing can inform operators about when to re-provision and increase network capacity.

TCP/IP and Linux protocol implementation : systems code for the Linux Internet

Abstract: Boasting high performance, high availability, and open source code, Linux has emerged as an optimal choice for an operating system Yet for Linux to be adopted by the mainstream of Unix-based corporate and ISP networks, it must be capable of supporting the TCP/IP Internet protocol, like any other network operating system This book provides the rapidly growing audience of Linux site managers, as well as researchers and developers worldwide, with the information they need on how Linux TCP/IP keeps the network running The authors walk readers through the Linux TCP/IP protocol stack, offering detailed explanations on how Linux implements its communications protocols

Components for Distributed Virtual Environments

Abstract: A virtual environment (VE) presents a complex problem with interesting nontrivial challenges for software development. The problems increase when considering VEs that are both distributed and shared among multiple participants. The majority of existing systems supporting large-scale VEs (LSVEs) are based on monolithic architectures, making maintenance and software reuse difficult at best. These problems have begun to be addressed by recent VE systems that employ software engineering principles in their design. Although modularity is addressed, many other issues remain unsolved, such as interoperability between different systems. The Java Adaptive Dynamic Environment (JADE) is presented as an alternative to the traditional approach for developing a core infrastructure for VE systems. JADE consists of a component framework along with a lightweight cross-platform kernel that permits system evolution at runtime and enables cross-system integration.

Preferential Treatment of Acknowledgment Packets in a Differentiated Services Network

Abstract: In the context of networks offering Differentiated Services (DiffServ), we investigate the effect of acknowledgment treatment on the throughput of TCP connections. We carry out experiments on a testbed offering three classes of service (Premium, Assured and Best-Effort), and different levels of congestion on the data and acknowledgment path. We apply a full factorial statistical design and deduce that treatment of TCP data packets is not sufficient and that acknowledgment treatment on the reverse path is a necessary condition to reach the targeted performance in DiffServ efficiently. We find that the optimal marking strategy depends on the level of congestion on the reverse path. In the practical case where Internet Service Providers cannot obtain such information in order to mark acknowledgment packets, we show that the strategy leading to optimal overall performance is to copy the mark from the respective data packet into returned acknowledgement packets, provided that the affected service class is appropriately provisioned.

Lower than best effort: a design and implementation

Abstract: In recent years, the Internet architecture has been augmented so that Better-than-Best-Effort (BBE) services, in the form of reserved resources for specific flows, can be provided by the network. To date, this has been realized through two different and sequentially developed efforts. The first is known as Integrated Services and focuses on specific bounds on bandwidth and/or delay for specific flows. The Differentiated Service model was later introduced, which presented a more aggregated and local perspective regarding the forwarding of traffic. A direction that is missing in today's work on service models is a defined schema used to purposely degrade certain traffic to various levels below that of Best Effort. In a sense, a new direction that provides a balancing effect in the deployment of BBE service. This is particularly evident with continual and parallel short transaction flows (like that used for web applications) over low bandwidth links that are not subject to any backoff penalty incurred by congestion because state does not persist. In a more indirect perspective, our model correlates degraded service with the application of usage and security policies -- administrative decisions that can operate in tandem or disjointly from conditions of the network. This paper attempts to address these and other issues and presents the design and implementation of such a new degraded service model and queuing mechanism used to support it.

Networked group communication : third International COST264 Workshop, NGC 2001, London, UK, November 7-9, 2001 : proceedings

Abstract: Application-Level.- Latency and User Behaviour on a Multiplayer Game Server.- Application-Level Multicast Using Content-Addressable Networks.- Scribe: The Design of a Large-Scale Event Notification Infrastructure.- Group Management.- Scamp: Peer-to-Peer Lightweight Membership Service for Large-Scale Group Communication.- Extremum Feedback for Very Large Multicast Groups.- An Overlay Tree Building Control Protocol.- Performance.- The Multicast Bandwidth Advantage in Serving a Web Site.- STAIR: Practical AIMD Multirate Multicast Congestion Control.- Impact of Tree Structure on Retransmission Efficiency for TRACK.- Security.- Framework for Authentication and Access Control of Client-Server Group Communication Systems.- Scalable IP Multicast Sender Access Control for Bi-directional Trees.- EHBT: An Efficient Protocol for Group Key Management.- Topology.- Aggregated Multicast with Inter-Group Tree Sharing.- Tree Layout for Internal Network Characterizations in Multicast Networks.

Quality of Future Internet Services: Second COST 263 International Workshop, Qofis 2001, Coimbra, Portugal, September 24-26, 2001. Proceedings

Abstract: QoS for Multimedia Communications- Design of Optimal Playout Schedulers or Packet Video Receivers- Constrained TCP-Friendly Congestion Control for Multimedia Communication- Adaptive Wavelet Video Filtering- On the Utility of FEC Mechanisms for Audio Applications- Admission Control- A Call Admission Control Method for Supporting Telephony Sessions in a Best Effort IP Network- Integrated Admission Control for Streaming and Elastic Traffic- Novel Enhancements to Load Control - A Soft-State, Lightweight Admission Control Protocol- PBAC: Probe-Based Admission Control- QoS Routing- QoS Routing: Average Complexity and Hopcount in m Dimensions- QoS Routing with Incomplete Information by Analog Computing Algorithms- Profile-Based Routing: A New Framework for MPLS Traffic Engineering- Differentiated Services Networks- Towards Better Support of Transaction Oriented Communication in Differentiated Services Networks- The Olympic Service Model: Issues and Architecture- Service Differentiation in ECN Networks Using Weighted Window-Based Congestion Control for Various Packet Marking Algorithms- Two-Differentiated Marking Strategies for TCP Flows in a Differentiated Services Network- QoS Monitoring and Mapping- Aguri: An Aggregation-Based Traffic Profiler- Traffic Handling in AQUILA QoS IP Network- The TCP Control Block Interdependence in Fixed Networks - Some Performance Results- Approaches to Support Differentiated Quality of Web Service- Traffic Engineering- Understanding the Long-Term Self-Similarity of Internet Traffic- Network Dimensioning with MPLS1- DSS: A Deterministic and Scalable QoS Provisioning Scheme- Invited Program- Experience with an IP QoS Physical Testbed: Problems and Research Issues- Affordable QoS in Future Wireless Networks: Myth or Reality ?