1432948
Exploiting diversity to enhance multimedia streaming over cellular links
Wireless wide area networks (WWANs) are becoming ubiquitous across most geographic regions, enabling simultaneous coverage from multiple providers. WWAN channels exhibit both uncorrelated and correlated behaviour on a variety of levels. In this paper we examine the statistical properties of WWAN links, and illustrate the benefits in heterogeneity that can be exploited to improve statistical throughput and multimedia quality. Our results are based on real network measurements. We describe the design and implementation of a high quality multimedia streaming application that implements WWAN streaming optimisations utilising unequal error protection coding techniques, and we evaluate the performance over an operational WWAN network.
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.
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.
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.
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.
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.
8594061
Data sharing and recovery in gigabit-networked databases
Major advances in optical fiber transmission and switching technology have enabled the development of very high speed networks with data rates of the order of gigabits per second. It is anticipated that in the future, wide area gigabit networks will interconnect database servers around the globe creating extremely powerful distributed information systems. In this paper, we examine the implications of such a high speed network on data access and sharing techniques and propose a lock-based concurrency control protocol and a log-based recovery protocol that ensures data consistency in gigabit-networked databases. Both protocols exploit the characteristics of a gigabit network to enhance the performance of the database system and, in particular, the fact that the size of the message is less of a concern than the number of sequential phases of message passing.
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>>
206616812
The Design, Implementation, and Use of the Ngram Statistics Package
The Ngram Statistics Package (NSP) is a flexible and easy-to-use software tool that supports the identification and analysis of Ngrams, sequences of N tokens in online text. We have designed and implemented NSP to be easy to customize to particular problems and yet remain general enough to serve a broad range of needs. This paper provides an introduction to NSP while raising some general issues in Ngram analysis, and summarizes several applications where NSP has been successfully employed. NSP is written in Perl and is freely available under the GNU Public License.
56684730
Extended Gloss Overlaps as a Measure of Semantic Relatedness
This paper presents a new measure of semantic relatedness between concepts that is based on the number of shared words (overlaps) in their definitions (glosses). This measure is unique in that it extends the glosses of the concepts under consideration to include the glosses of other concepts to which they are related according to a given concept hierarchy. We show that this new measure reasonably correlates to human judgments. We introduce a new method of word sense disambiguation based on extended gloss overlaps, and demonstrate that it fares well on the SENSEVAL-2 lexical sample data.
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.