Tim Moors

Survey of research towards robust peer-to-peer networks: search methods

The pace of research on peer-to-peer (P2P) networking in the last five years warrants a critical survey. P2P has the makings of a disruptive technology--it can aggregate enormous storage and processing resources while minimizing entry and scaling costs. Failures are common amongst massive numbers of distributed peers, though the impact of individual failures may be less than in conventional architectures. Thus the key to realizing P2Ps potential in applications other than casual file sharing is robustness.P2P search methods are first couched within an overall P2P taxonomy. P2P indexes for simple key lookup are assessed, including those based on Plaxton trees, rings, tori, butterflies, de Bruijn graphs and skip graphs. Similarly, P2P indexes for keyword lookup, information retrieval and data management are explored. Finally, early efforts to optimize range, multiattribute, join and aggregation queries over P2P indexes are reviewed. Insofar as they are available in the primary literature, robustness mechanisms and metrics are highlighted throughout. However, the low-level mechanisms that most affect robustness are not well isolated in the literature. Furthermore, there has been little consensus on robustness metrics. Recommendations are given for future research.

Support of voice services in IEEE 802.11 wireless LANs

The IEEE 802.11 MAC protocol supports two modes of operation, a random access mode for non-real-time data applications, and a polling mode for real-time applications. We design and analyze a system that uses the polling mode for interactive voice traffic. With larger inter-poll periods, more voice calls can be accommodated, but at the expense of increased delay. For example, our analysis shows that with an inter-poll period of 90 ms, a maximum of 26 voice calls can be handled with a worst-case delay of 303 ms, whereas with an inter-poll period of 60 ms, a maximum of 17 voice calls can be handled with a worst-case delay of 213 ms. We also carry out an error analysis that demonstrates the need for error correction of voice packets.

Call admission control for IEEE 802.11 contention access mechanism

This paper proposes an admission control algorithm that enables the upcoming IEEE 802.11e contention based enhanced distributed channel access (EDCA) to provide quantitative bandwidth guarantees for wireless local area networks (WLANs), rather than a relative prioritized service. The algorithm estimates the throughput that flows would achieve if a new flow with certain parameters was admitted, and so indicates whether such a new flow can be admitted while preserving the quality of service (QoS) of existing flows. The algorithm deals with the EDCA parameters of minimum contention window size and transmission opportunity duration, and indicates what values should be used for different flows. Simulation results confirm the accuracy of the throughput estimates and the effectiveness of the admission control algorithm.

Fairness and capacity trade-off in IEEE 802.11 WLANs

The paper investigates fairness in a wireless LAN environment in which stations experience unequal signal qualities due to location and interference factors. This causes differences in transmission rate among mobile stations due to the use of link adaptation schemes. We analyse fairness in the presence of these impairments for the distributed contention based access mechanisms of the IEEE 802.11 and 802.11e standards. The notion of fairness is explored in terms of utility derived from the network (i.e. throughput) and allocated resources (i.e. amount of time permitted to transmit). We show how fairness can be achieved by judicious choice of parameters and study the impact of these choices on capacity. Finally, we demonstrate how these findings could affect other related designs including admission control and charging schemes.

Architectures and protocols that enable new applications on optical networks

This article first discusses how advances in networking architectures and protocols can complement advances in optical communications research to increase the overall value of optical networks by enabling more applications. A review of existing optical networking solutions is then provided along with a classification of different types of optical networks. Finally, we show how single-hop and multihop wavelength-routed networks can be used efficiently for fast end-to-end file transfers when these networks are equipped with a hardware-implementable signaling protocol, a routing protocol, and a simple transport protocol.

Cascading content-addressable memories

The various methods of connecting multiple content-addressable memory (CAM) devices to form a memory system of larger dimensions are surveyed. They include daisy-chaining CAMs to increase the number of elements and possibly using carry-lookahead logic to increase the cascade. To increase the data size, one can replicate the labels in distinct CAMs, use the data storage available in a primary CAM to index a secondary CAM/RAM (read-only memory), or reduce redundancy in labels. To increase the label size, one can use an element cascade with or without a shift register, a master-slave cascade, or a trie cascade. One of the methods examined for increasing the label size is a new trie cascade approach.<<ETX>>

Virtualizing the access network via open APIs

Residential broadband consumption is growing rapidly, increasing the gap between ISP costs and revenues. Meanwhile, proliferation of Internet-enabled devices is congesting access networks, frustrating end-users and content providers. We propose that ISPs virtualize access infrastructure, using open APIs supported through SDN, to enable dynamic and controlled sharing amongst user streams. Content providers can programmatically provision capacity to user devices to ensure quality of experience, users can match the degree of virtualization to their usage pattern, and ISPs can realize per-stream revenues by slicing their network resources. Using video streaming and bulk transfers as examples, we develop an architecture that specifies the interfaces between the ISP, content provider, and user. We propose an algorithm for optimally allocating network resources, leveraging bulk transfer time elasticity and access path space diversity. Simulations using real traces show that virtualization can reduce video degradation by over 50%, for little extra bulk transfer delay. Lastly, we prototype our system and validate it in a test-bed with real video streaming and file transfers. Our proposal is a first step towards the long-term goal of realizing open and agile access network service quality management that is acceptable to users, ISPs and content providers alike.

A critical review of "End-to-end arguments in system design"

The end-to-end arguments raised by J. Saltzer, D. Reed and D. Clark (see ACM Trans. Comp. Sys., vol.2, no.4, p.277-88, 1984) are amongst the most influential of all communication protocol design guides. However, they have recently been challenged by the advent of firewalls, caches, active networks, NAT (network address translators), multicasting and network QoS. This paper reviews the end-to-end arguments, highlighting their subtleties, and provides additional arguments for and against end-to-end implementations. It shows the importance of trust as a criterion for deciding whether to implement a function locally or end-to-end, and how end-to-end implementations can help robustness, scalability, ease of deployment, and the provision of appropriate services. It focuses on the performance implications of end-to-end or localized functionality and argues against end-to-end congestion control of the form used by TCP.

Interference-aware Multipath Selection for Reliable Routing in Wireless Mesh Networks

This paper investigates the problem of selecting multiple routing paths to provide better reliability in multi-radio, multi-channel mesh networks with stationary nodes. Providing reliability is difficult in wireless networks because of unreliable transmissions. Previous work has investigated the use of additional data redundancy to improve the packet delivery rate, but requires node-disjoint paths to be used. In this paper we investigate multipath routing with packet duplication and non-disjoint paths for achieving better reliability and low delay. We propose a path weight function based on the ETT metric and interference minimisation. Our solution provides higher packet delivery ratio and lower end-to-end delay when compared to the single path WCETT metric, a maximally disjoint path selection metric, and the CAM metric.

ATM receiver implementation issues

Issues arising in the implementation of receivers for asynchronous transfer mode (ATM) networks, e.g., IEEE Std 802.6 MANs (metropolitan area networks) and broadband integrated services digital networks (B-ISDNs), are examined. These include buffering strategies to account for the burstiness and spatial randomness of buffering demands, preventing reassembly deadlock, and enforcing packet reception precedences. It is shown that transnode delays critically affect protocol performance and the complexity of implementing spatial reuse. >