711206
Performance optimizations for wireless wide-area networks: comparative study and experimental evaluation
We present a comparative performance study of a wide selection of optimization techniques to enhance application performance in the context of wide-area wireless networks (WWANs). Unlike in traditional wired and wireless IP-based networks, applications running over WWAN cellular environments are significantly affected by the vagaries of the cellular wireless medium. Prior research has proposed and analyzed optimizations at individual layers of the protocol stack. In contrast, we introduce the first detailed experiment-based evaluation and comparison of all such optimization techniques in a commercial WWAN testbed. This paper, therefore, summarizes our experience in implementing and deploying an infrastructure to improve WWAN performance.The goals of this paper are: (1) to perform an accurate benchmark of application performance over such commercially deployed WWAN environments, (2) to implement and characterize the impact of various optimization techniques across different layers of the protocol stack, and (3) to quantify their interdependencies in realistic scenarios. Additionally, we also discuss measurement pitfalls that we experienced and provide guidelines that may be useful for future experimentation in WWAN environments.
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.
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.
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.
13128696
Media-friendliness of a slowly-responsive congestion control protocol
Streaming media transfers over the Internet are expected to behave in a TCP-friendly manner while reacting slower to congestion than TCP. For this purpose, a number of slowly-responsive congestion control protocols have been developed. In this paper, we present our study on the media-friendliness of TFRC, one of the recently developed slowly-responsive congestion control mechanisms. With both simulation and Internet experiments, we show that TFRC is not necessarily smooth enough to be "media-friendly". We also discuss our approach to improve a congestion control mechanism's media-friendliness.
8291592
Performance analysis of the send-on-demand: A distributed database concurrency control protocol for high-speed networks
In this paper, we consider an application of high-speed wide area networks, viz. that of distributed database systems (DDBS). In a high-speed environment, although the transmission delay decreases, the propagation delay (communication latency) now becomes the throughput thwarting factor. Existing Concurrency Control (CC) protocols do not address the communication latency problem. This paper is a continuation of our research work in this area. First, we very briefly summarize our previously reported research results, viz. the issues that are important for DDBS in high-speed wide area networks, and the description of a new CC protocol called 'send-on-demand'. A detailed comparison of this protocol with that of locking is provided, using analytical and simulation techniques. The datacycle scheme performs very well in a read-oriented environment, and the rest of the paper deals with developing and comparing hybrid CC schemes using datacycling for queries. Altogether, the performance of four concurrency control schemes is compared.
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.
9170580
Network latency optimizations in distributed database systems
The advent of high-speed networks will enable the deployment of data-server systems (currently used in LANs) over WANs. The users of these systems will have the same high expectations with respect to performance parameters (such as the transaction throughput, response time and system reliability) as in the case of LANs. Thus, it is important to study the performance of existing distributed database protocols in the new networking environment, identify the performance bottlenecks and develop protocols that are capable of taking advantage of the high-speed networking technology. As a first step, in this paper, we examine the scalability of the server-based two-phase locking (s-2PL) protocol, and discuss three optimizations which allow the s-2PL protocol to be tailored for high-speed WAN environments where the size of the message is less of a concern than the number of rounds of message passing. These optimizations, collectively called the group two-phase locking (g-2PL) protocol, reduce the number of rounds of message passing by grouping lock grants, client-end caching and data migration. In a simulation study, 20-25% improvement in the response time of the g-2PL protocol over that of the s-2PL protocol was observed.
17465088
An efficient channel-feedback-based adaptive protocol for scheduling variable-length messages on slotted, high-speed fiber optic LANs/MANs
This paper is based on the continuation-bit approach in conjunction with a probabilistic scheduling strategy called the p/sub i/-persistent protocol. This combination has been proposed as an efficient multiple access protocol for transmitting variable-length messages on slotted, high-speed, fiber-optic, bus-structured local and metropolitan area networks (LANs/MANs). Specifically, the authors extend the previous static model on this approach to the dynamic case so that the protocol can be implemented. A dynamic simulation model of the protocol using the continuation-bit approach has been formulated, and channel feedback information has been used to calibrate the operating parameters in real time. Since the goal was to study the operation of the dynamic protocol with variable-length messages, variable-bit-rate coded (i.e., compressed) video was chosen as the traffic to be carried by the network in the illustrative examples. The simulation model indicates that channel feedback is a good approach for dynamically adjusting the network parameters as the network loading and the message lengths fluctuate. Even at a network utilization of 0.6, it was found that almost all video messages were transmitted from the station buffers before the next video message arrived.<<ETX>>