2103105
The Interdomain Connectivity of PlanetLab Nodes
In this paper we investigate the interdomain connectivity of PlanetLab nodes. We note that about 85 percent of the hosts are located within what we call the Global Research and Educational Network (GREN) — an interconnected network of high speed research networks such as Internet2 in the USA and Dante in Europe. Since traffic with source and destination on the GREN is very likely to be transited solely by the GREN, this means that over 70 percent of the end-to-end measurements between PlanetLab node pairs represent measurements of GREN characteristics. We suggest that it may be possible to systematically choose the placement of new nodes so that as the PlanetLab platform grows it becomes a closer and closer approximation to the Global Internet.
8584874
Throughput Optimization and Fair Bandwidth Allocation in Multi-Hop Wireless LANs
There is an inherent well-known conflict between fairness and throughput that arises in many networking scenarios. A number of researchers have studied this problem in the context of (single-hop) wireless local area networks (WLANs), where clients directly exchange traffic with access points (APs). More recently, researchers have proposed multi-hop extensions to WLANs where client traffic is forwarded via a series of client-client links. In this paper, we show that the objective of improving throughput without sacrificing fairness can be much better met in multi-hop WLANs. We decouple this objective into two separate but related problems. First, we need an algorithm to organize clients into a multi-hop structure such that fair bandwidth allocation within this structure leads to improved throughput. Second, we need algorithms for performing fair bandwidth allocation within the determined multi-hop structure. In this paper, we first design optimal fair bandwidth allocation algorithms for both max-min throughput fairness and max-min time fairness in multi-hop WLANs. Subsequently, we design an efficient algorithm to find desirable multi-hop structures. With slight modifications, our results in this paper can be generalized to other multi-hop wireless networks as well. Our proposed solutions seamlessly integrate with legacy devices and hence are incrementally deployable. Simulation results demonstrate that our solutions can effectively improve throughput (by up to 114% or more) as well as network coverage while preserving fairness.
3056111
An Analysis of Wireless Network Coding for Unicast Sessions: The Case for Coding-Aware Routing
A recent approach, COPE, for improving the throughput of unicast traffic in wireless multi-hop networks exploits the broadcast nature of the wireless medium through opportunistic network coding. In this paper, we analyze throughput improvements obtained by COPE-type network coding in wireless networks from a theoretical perspective. We make two key contributions. First, we obtain a theoretical formulation for computing the throughput of network coding on any wireless network topology and any pattern of concurrent unicast traffic sessions. Second, we advocate that routing be made aware of network coding opportunities rather than, as in COPE, being oblivious to it. More importantly, our work studies the tradeoff between routing flows "close to each other" for utilizing coding opportunities and "away from each other" for avoiding wireless interference. Our theoretical formulation provides a method for computing source-destination routes and utilizing the best coding opportunities from available ones so as to maximize the throughput. We handle scheduling of broadcast transmissions subject to wireless transmit/receive diversity and link interference in our optimization framework. Using our formulations, we compare the performance of traditional unicast routing and network coding with coding-oblivious and coding-aware routing on a variety of mesh network topologies, including some derived from contemporary mesh network testbeds. Our evaluations show that a route selection strategy that is aware of network coding opportunities leads to higher end-to-end throughput when compared to coding-oblivious routing strategies.
15760
Energy-Efficient Reliable Paths for On-Demand Routing Protocols
We define techniques to compute energy-efficient reliable paths within the framework of on-demand routing protocols. The choice of energy-efficient reliable paths depend on link error rates on different wireless links, which in turn depend on channel noise. We show how our scheme accounts for such channel characteristics in computing such paths. Additionally, we perform a detailed study of the AODV protocol and our energy-efficient variants, under various noise and node mobility conditions. Our results show that our proposed variants of on-demand routing protocols can achieve orders of magnitude improvement in energy-efficiency of reliable data paths.
14357613
Construction of an efficient overlay multicast infrastructure for real-time applications
This paper presents an overlay architecture where service providers deploy a set of service nodes (called MSNs) in the network to efficiently implement media-streaming applications. These MSNs are organized into an overlay and act as application-layer multicast forwarding entities for a set of clients. We present a decentralized scheme that organizes the MSNs into an appropriate overlay structure that is particularly beneficial for real-time applications. We formulate our optimization criterion as a "degree-constrained minimum average-latency problem" which is known to be NP-hard. A key feature of this formulation is that it gives a dynamic priority to different MSNs based on the size of its service set. Our proposed approach iteratively modifies the overlay tree using localized transformations to adapt with changing distribution of MSNs, clients, as well as network conditions. We show that a centralized greedy approach to this problem does not perform quite as well, while our distributed iterative scheme efficiently converges to near-optimal solutions.
11368060
Packet classifiers in ternary CAMs can be smaller
Serving as the core component in many packet forwarding, differentiating and filtering schemes, packet classification continues to grow its importance in today's IP networks. Currently, most vendors use Ternary CAMs (TCAMs) for packet classification. TCAMs usually use brute-force parallel hardware to simultaneously check for all rules. One of the fundamental problems of TCAMs is that TCAMs suffer from range specifications because rules with range specifications need to be translated into multiple TCAM entries. Hence, the cost of packet classification will increase substantially as the number of TCAM entries grows. As a result, network operators hesitate to configure packet classifiers using range specifications. In this paper, we optimize packet classifier configurations by identifying semantically equivalent rule sets that lead to reduced number of TCAM entries when represented in hardware. In particular, we develop a number of effective techniques, which include: trimming rules, expanding rules, merging rules, and adding rules. Compared with previously proposed techniques which typically require modifications to the packet processor hardware, our scheme does not require any hardware modification, which is highly preferred by ISPs. Moreover, our scheme is complementary to previous techniques in that those techniques can be applied on the rule sets optimized by our scheme. We evaluate the effectiveness and potential of the proposed techniques using extensive experiments based on both real packet classifiers managed by a large tier-1 ISP and synthetic data generated randomly. We observe significant reduction on the number of TCAM entries that are needed to represent the optimized packet classifier configurations.
7265407
A Database Platform for Bioinformatics
In recent years, new developments in genetics have generated a lot of interest in genomic and proteomic data, investing international significance (and competition) in the fledgling discipline of bioinformatics. Researchers in pharmaceutical and biotech companies have found that database products can bring a wide range of relevant technologies to bear on their problems. Benefiting from a number of new technology enhancements, Oracle has emerged as a popular platform for pharmaceutical knowledge management and bioinformatics. We look at four powerful technologies that show promise for solving hitherto intractable problems in bioinformatics: the extensibility architecture to store gene sequence data natively and perform high-dimensional structure-searches in the database; warehousing technologies and data mining on genetic patterns; data integration technologies to enable heterogeneous queries across distributed biological sources, and internet portal technologies that allow life sciences information to be published and managed across intranets and the internet.
15094516
Translating application requirements to ATM cell level requirements
It has been well established that high speed networks will be based on cell relay technology, an important feature of which is small fixed size packets. However, application data is rarely small of fixed size, and hence it is important to study the impact on message-level performance in a cell based system. This paper presents a simulation study of application level performance and studies various trade-offs in requesting specific cell level QoS parameters to satisfy the application requirements.
52854658
Adaptive bandwidth control for efficient aggregate QoS provisioning
Internet links operate at high speeds, and past trends predict that these speeds will continue to increase rapidly. Routers and Intrusion Detection Systems that operate at up to OC-768 speeds (40 Gigabits/second) are currently being developed. In this paper we address a basic function common to several security and measurement applications running at line speeds: counting the number of distinct header patterns (flows) seen on a high speed link in a specified time period. For example one can detect port scans by counting the number of connections opened by the suspected port scanner and one can ascertain that a denial of service attack is in progress by counting the number of distinct (fake) source addresses that send packets to the suspected victim. We provide algorithms solving the flow counting problem using extremely small amounts of memory. This can translate into savings of scarce fast memory (SRAM) for hardware implementations. It can also help systems that use cheaper DRAM to allow them to scale to larger instances of the problem. The reduction in memory is particularly important for network security applications such as detecting port scans and DoS attacks that need to run a separate instance of the algorithm for each suspected attacker or victim. Our algorithms can be implemented in hardware at wire speeds (8 nsec per packet for OC-768) using simple CRC based hash functions, multiplexers and SRAM. They access at most one or two memory locations per packet. We expose the behavior of simple building blocks and provide a family of customizable counting algorithms that can be adapted to the requirements of various applications. This allows our algorithms to use less memory than the best known counting algorithm, probabilistic counting, to provide the same accuracy. • Virtual bitmap is well suited for triggers (which need only be accurate around a threshold value) such as detecting DoS attacks, and uses 292 bytes to achieve an error of 2.619% compared to 5,200 bytes for probabilistic counting. • Our “no assumptions” counting algorithm, multiresolution bitmap algorithms uses only 2143 bytes to count up to 100 million flows with an average error of 3%. Its accuracy is slightly better when the number of flows is small, while the accuracy of probabilistic counting using the same memory is much worse. • Our adaptive bitmap that exploits stationarity in the number of flows can count the number of distinct flows on a link that contains anywhere from 0 to 100 million flows with an average error of less than 1 % using only 2 Kbytes of memory. Probabilistic counting needs eight times more memory to achieve the same accuracy. • We used our triggered bitmap to replace the port scan detection component of the popular intrusion detection system Snort. Doing so reduced the memory usage from 89 Mbytes to 6.4 Mbytes (with an average error of 13.5%) as measured on a 10 minute trace. Probabilistic counting uses 23 Mbytes. This work was made possible by a grant from NIST for the Sensilla Project. King: Estimating Latency between Arbitrary Internet End Hosts ∗ Krishna P. Gummadi, Stefan Saroiu, Steven D. Gribble Department of Computer Science & Engineering University of Washington Seattle, WA, USA, 98195-2350 {tzoompy,gummadi,gribble}@cs.washington.edu The ability to estimate network latencies accurately between arbitrary Internet end hosts would enable wide-area measurement studies and applications, such as investigating routing path inefficiencies on a wide-scale [1] or constructing topologically sensitive overlay networks. In this poster we present King [2], a tool that accurately, quickly and cheaply estimates the latency between arbitrary end hosts by using existing DNS infrastructure in a novel way. Our approach is inspired by tools like Sting [3] and TBIT [4], which show that it is possible to use existing protocols in unanticipated ways to obtain results that were previously intractable. Our technique relies on two observations. First, given a pair of end hosts to be measured, in most cases it is possible for King to find their authoritative DNS name servers that are topologically close to the end hosts. Second, given a pair of DNS name servers, King can accurately estimate the latency between them using recursive DNS queries. Thus, King is able to use the measured latency between the name servers as an estimate of the latency between the end hosts. Although this estimate will inevitably suffer from inaccuracies, our extensive evaluation demonstrates that this estimation error is small (less than 20% error in over three-quarters of generated estimates). Compared to previous approaches like IDMaps [5] and GNP [6], King has two primary advantages (1) deployability and (2) accuracy. 1. Deployability: Unlike IDMaps, King does not require the deployment of additional infrastructure, and unlike GNP, King does not require end hosts to agree upon a single set of landmarks or share the coordinates with other end hosts. Because King uses existing DNS infrastructure, it scales naturally in terms of the number hosts that could be measured. Our evaluation indicates that King can be used to estimate latencies between arbitrary IP hosts more than 75% of time in the Internet today. 2. Accuracy: Unlike IDMaps and GNP the accuracy of King is not affected by the placement of measurement points (tracers or landmarks) in the Internet. King’s estimates are based on direct online measurements rather than extrapolation from latencies This work was supported by National Science Foundation under ITR grant No. CCR-0121341. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. of a subset of paths measured offline. Our evaluation shows that the error in King latency estimates between end hosts is significantly smaller than that of IDMaps, while the error in its estimates between name servers is negligible. Further, we show that King can identify those of its own estimates that are likely to be inaccurate. These characteristics make King an ideal tool for a number of wide-area measurement studies that involve measuring latencies accurately between a large number of geographically distant end hosts. King is also fast and lightweight requiring the generation of only a few packets to produce an estimate. Our evaluation also demonstrates that (a) King preserves order among its latency estimates; a feature useful in identifying a close server from a group of server replicas and (b) authoritative name servers are located topologically close to their end hosts in a majority of scenarios (i.e., latencies as measured from a far away host to both the end host and its name server are very similar); this explains the high accuracy of King. Finally, we test the feasibility of using King for measurement studies by performing Detour study [1] on a larger scale. The results we obtained are consistent with the earlier Detour study. We were able to obtain our results with far greater ease as, unlike the previous study, we were not restricted to the publicly available traceroute servers and their usage policies. We also believe that the simplicity of our King tool will enable researchers to use it in myriads of unanticipated ways like the more popular Ping tool.
43624883
Algorithms for optimized node arrangements in ShuffleNet based multihop lightwave networks
The unique capabilities of lightwave technology are exploited in order to construct optimized regular multihop networks when the traffic flow among the network nodes is asymmetric. The specific problem addressed is as follows: given that the network nodes must be connected in a regular interconnection pattern and that the node positions in the regular network can be adjusted by properly tuning their (optical) transceivers, what is the best node placement in a given regular topology? In particular, the ShuffleNet-based regular topology is examined. ShuffleNet has the property of producing large connected graphs with small degree and diameter. In order words, it can interconnect a large number of nodes with a small number of transceivers per node such that information from a source can reach its destination in a small number of hops. Since finding the optimal node placement is a computationally hard problem, efficient heuristic algorithms are formulated to design optimized ShuffleNet structures for a given traffic matrix.<<ETX>>
16981937
Network traffic characterization of distributed database applications
The authors' efforts in characterizing the traffic of distributed database systems are described. This is an important class of applications considering that database or transaction processing systems form the core of several key commercial applications. Specific traffic source models for this application class have not been developed which is imperative for their successful deployment in emerging networks. The main contribution of the paper is to present the relationship between a distributed database application scenario and the corresponding network traffic characteristics, thus providing guidelines to these applications to compute their traffic descriptors accurately.